Comparison of circulating tumor DNA between African American and Caucasian patients with metastatic castrate-resistant prostate cancer post-abiraterone and/or enzalutamide

BACKGROUND

African American men are much more likely than Caucasian men to be diagnosed with and to die of prostate cancer. Genetic differences likely play a role. The cBioPortal database reveals that African American men with prostate cancer have higher rates of CDK12 somatic mutations compared to Caucasian men. However, this does not account for prior prostate cancer treatments, which are particularly important in the castrate-resistant setting. We aimed to compare somatic mutations based on circulating tumor DNA (ctDNA) in metastatic castration-resistant prostate cancer (mCRPC) between African American and Caucasian men after exposure to abiraterone and/or enzalutamide.

METHODS

This single-institution retrospective study characterizes the somatic mutations detected on ctDNA for African American and Caucasian men with mCRPC who had progressed after abiraterone and/or enzalutamide from 2015 through 2022. We evaluated the gene mutations and types of mutations in this mCRPC cohort.

RESULTS

There were 50 African American and 200 Caucasian men with CRPC with available ctDNA data. African American men were younger at the time of diagnosis (p = 0.008) and development of castration resistance (p = 0.006). African American men were more likely than Caucasian men to have pathogenic/likely pathogenic (P/LP) mutations in CDK12 (12% vs. 1.5%; p = 0.003) and copy number amplifications and P/LP mutations in KIT (8.0% vs. 1.5%; p = 0.031). African American men were also significantly more likely to have frameshift mutations (28% vs. 14%; p = 0.035).

CONCLUSIONS

Compared to Caucasian men, African American men with mCRPC after exposure to abiraterone and/or enzalutamide had a higher incidence of somatic CDK12 P/LP mutations and KIT amplifications and P/LP mutations based on ctDNA. African American men also had more frameshift mutations. We hypothesize that these findings have potential implications for tumor immunogenicity.

Abstract 6698: Combinatorial genomic and epigenomic cell-free DNA analysis of high-risk metastatic castration resistant prostate cancer reveals prognostic liquid biopsy signatures

Background: Androgen receptor signaling inhibitors (ARSI) such abiraterone and enzalutamide have significantly improved clinical outcomes in metastatic castrate-resistant prostate cancer (mCRPC) patients. However, patients with genomic alterations in the androgen receptor (AR) and its enhancer region do not respond well and acquire resistance to these inhibitors. Here, we applied our previously developed cell-free DNA (cfDNA) liquid biopsy assay (EnhanceAR-Seq) to detect these high-risk mCRPC patients prior to the administration of first-line AR-directed therapy and correlated with survival. We also interrogated the plasma methylome to identify differentially methylated regions (DMRs) across these high-risk patients. Methodology: We applied EnhanceAR-Seq to plasma cfDNA isolated from 99 mCRPC patients enrolled from two institutions (n=52 Tulane; n=47 WashU). Plasma samples were collected prior to ARSI initiation (n=63) or during treatment (n=36). We also performed Enzymatic Methyl-seq in pre-treatment plasma from 43 patients. We split these 43 patients into cell-free genomically high-risk and low-risk groups using our EnhanceAR-seq results, and conducted DMR analysis using metilene. To identify significant DMRs, we performed multiple hypothesis testing and required q<0.05 using the Benjamini-Hochberg procedure, and further required at least 5 CpGs per DMR. Results: EnhanceAR-Seq detected AR/enhancer alterations in 35% of all plasma samples. Cell-free AR/enhancer detection was highly prognostic (PFS HR=2.80, p=0.0002; OS HR=2.6, p=0.01). When considering only pre-treatment plasma, AR/enhancer alterations detected in 44% (28/63) of samples correlated significantly with worse PFS (HR=2.21, p=0.009) and OS (HR=2.60, p=0.02). AR/enhancer alterations detected in 19% (7/36) of samples collected during ARSI were also associated with worse PFS (HR=15.6, p=0.0002) and OS (HR=8.09, p=0.05). Plasma methylome analysis revealed that for cell-free genomically high-risk mCRPC patients (based on AR/enhancer alterations detected in cfDNA), significantly hypomethylated DMRs were found in the AR promoter, upstream AR enhancer, and in AR-associated genes including FOXP1 and FOLH1. Significantly hypomethylated DMRs were also observed in DNA damage repair and cell cycle genes including MSH6, MSH3, FANCD2, CDK12 and RAD51B. Hypermethylated DMRs were seen in tumor suppressor genes including ZBTB16, BRCA2, WT1 and GNAS. Conclusions: AR/enhancer alterations detected in plasma cfDNA predicted inferior survival in mCRPC patients. Cell-free genomically high-risk mCRPC patients could be distinguished from low-risk patients based on distinct methylation signatures.

Citation Format: Irfan Alahi, Pradeep S. Chauhan, Alexander L. Shiang, Jace Webster, Ha X. Dang, Lilli Greiner, Breanna yang, Elisa M. Ledet, Ramandeep K. Babbra, Wenjia Feng, Peter K. Harris, Ellen B. Jaeger, Patrick J. Miller, Sydney A. Caputo, Giordano Cittolin Santos, Oliver Sartor, Russell K. Pachynski, Christopher A. Maher, Aadel A. Chaudhuri. Combinatorial genomic and epigenomic cell-free DNA analysis of high-risk metastatic castration resistant prostate cancer reveals prognostic liquid biopsy signatures [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6698.

Clinical and Genetic Analysis of Metastatic Prostate Cancer to the Central Nervous System: A Single-Institution Retrospective Experience

BACKGROUND

Prostate cancer (PC) rarely metastasizes to the central nervous system (CNS). In this retrospective single-institution study at a tertiary cancer center, we aimed to evaluate the clinical and genetic characteristics of advanced PC patients with CNS metastases.

PATIENTS AND METHODS

Between January 2010 and March 2020, 12 out of 579 patients with extracranial metastatic PC were identified to have CNS metastases based on imaging, including six patients with brain metastases (BMs), five patients with dural metastases, and one unknown. These patients were followed up through March 2022. Clinical data were compared to the overall cohort of patients evaluated at our cancer center during that decade. Genetics information was also analyzed for the patients with available data via cell-free DNA (cfDNA) blood samples.

RESULTS

Median time from development of extracranial metastatic disease to development of CNS metastases was 5.5 years (95% CI, 1.8-7.0). Median overall survival (mOS) from diagnosis of CNS metastases was 6.1 months (95% CI, 5.8-8.2). Notably, there was no significant difference in mOS after development of extracranial metastases in patients with CNS metastases (6.4 years; 95% CI, 4.6-7.9) compared to the patients without known CNS metastases (5.2 years; 95% CI, 4.6-5.7) (P = .91). For the cohort with CNS metastases, nine patients had germline testing and seven patients had somatic testing via cfDNA.

CONCLUSION

PC patients with CNS metastases did not often die from a neurological cause. With advancing therapies, the overall prognosis of metastatic PC continues to improve, and CNS metastases will become more common.

Clinical and Molecular Determinants of PSA Response to Bipolar Androgen Therapy in Prostate Cancer

BACKGROUND

Bipolar Androgen Therapy (BAT) is a novel therapy known to be effective in a subset of men with metastatic castrate resistant prostate cancer (mCRPC). A better understanding of responders and non-responders to BAT would be useful to clinicians considering BAT therapy for patients. Herein we analyze clinical and genetic factors in responders/non-responders to better refine our understanding regarding which patients benefit from this innovative therapy.

METHODS

mCRPC patients were assessed for response or no response to BAT. Patients with PSA declines of greater than 50% from baseline after 2 or more doses of testosterone were considered to be responders. Whereas, Non-responders had no PSA decline after 2 doses of testosterone and subsequently manifest a PSA increase of >50%. Differences between these two groups of patients were analyzed using clinical and laboratory parameters. All patients underwent genomic testing using circulating tumor DNA (ctDNA) and germline testing pre-BAT.

RESULTS

Twenty five patients were non-responders and 16 were responders. Baseline characteristics between non-responders and responders varied. Responders were more likely to have had a radical prostatectomy as definitive therapy and were more likely to have been treated with an androgen receptor (AR) antagonist (enzalutamide or apalutamide) immediately prior to BAT (compared to abiraterone). Duration of prior enzalutamide therapy was longer in responders. Non-responders were more likely to have bone-only metastases and responders were more likely to have nodal metastases. Assays detected ctDNA AR amplifications more often in responding patients. Responders trended toward having the presence of more TP53 mutations at baseline.

CONCLUSIONS

BAT responders are distinct from non-responders in several ways however each of these distinctions are imperfect. Patterns of metastatic disease, prior therapies, duration of prior therapies, and genomics each contribute to an understanding of patients that will or will not respond. Additional studies are needed to refine the parameters that clinicians can utilize prior to choosing among the numerous treatment alternatives available for CRPC patients. This article is protected by copyright. All rights reserved.

Characterization of ctDNA findings at the end of life in patients with prostate cancer

230

Background: Somatic alterations change over time in response to treatment and disease progression in patients with prostate cancer (PCa). We report ctDNA findings of patients who died from PCa within 3 months of a ctDNA assessment to better characterize patients with fatal disease. Methods: A total of 118 patients with PCa specific mortality who had been treated at Tulane Cancer Center and had ctDNA assessments between 2015 and 2022. The ctDNA was assessed by Guardant360 (Guardent Health, Inc) assays to identify alterations, pathogenic mutations and/or copy number alterations (CNAs) in cancer-related genes. Clinical annotation including treatment history, genetics, and staging were also obtained. Statistical analyses included Fischer’s Exact and Wilcoxon tests. Results: Of the 118 patients with PCa specific mortality, 42% (49/118) had a ctDNA assessment <3 months from death. Of 49 CRPC patients tested within 3 months of death, the median number of life extending therapies (LET) at death was 5 (2-9). Patients had a median of 2 (0-6) LET prior to first ctDNA screening and 3 (0-7) LET in between first and last ctDNA assessment. Of the total gene alterations detected on ctDNA analysis, within 3 months of death, the most common alterations detected were 65.3% (32/49) TP53, 44.9% (22/49) AR, 28.6% (14/49) EGFR, 24.5% (12/49) PIK3CA, 22.4% (11/49) MYC, and 20.4% (10/49) CDK6. In a paired analysis(n= 45) of first and last ctDNA screening, AR (OR= 2.35, 95% C.I. (0.99, 5.62), p= 0.05), CDK6 (OR= 4.00, 95% C.I. (1.02, 15.68), p= 0.04), FGFR1 (OR= 9.51, 95% C.I. (1.14, 79.61), p= 0.03), and EGFR (OR= 9.71, 95% C.I. (2.06, 45.83), p= 0.0009) were significantly more likely to be detected in ctDNA screening within 3 months of death. In addition, ctDNA alterations in general were significantly more likely to be detected at the end-of-life (p=< 0.00001). Other ctDNA gene mutations did not have statistically significant increases. Conclusions: An analysis of patients with PCa mortality showed most frequent gene alterations in TP53, AR, EGFR, PIK3CA, MYC, and CDK6. When comparing patients’ first and last ctDNA, alterations were significantly more likely by time of death in AR, CDK6, EGFR, FGFR and there was a significant increase in overall detection of somatic alterations in ctDNA. These analyses are limited to the genes assessed on the ctDNA panel and may or may not reflect all of the functionally relevant alterations. Further the CNAs reported herein may reflect broad genomic changes rather than specific gene alterations.

Comparison of ctDNA between African American and Caucasian patients with CRPC post abiraterone and/or enzalutamide

35

Background: Genetic differences between African American and Caucasian patients with advanced prostate cancer may contribute to racial disparities in terms of treatment outcomes and survival, hence further exploration is warranted. We assessed ctDNA differences between African American and Caucasian men in the setting of CRPC post treatment with abiraterone and/or enzalutamide. Methods: From 2015 through 2022 at Tulane Cancer Center, 250 patients with CRPC including 50 African Americans and 200 Caucasian with prior abiraterone and/or enzalutamide treatment were included. All patients had ctDNA assessed via Guardant360. Data including both gene mutations and types of mutations were for between 73-80 genes. Clinical annotation including initial staging, treatment history, and genetic testing were obtained. Statistical analyses included Fisher’s exact test and Wilcoxon rank-sum test. Results: The most common pathogenic/likely pathogenic (P/LP) alterations in both African Americans and Caucasians were TP53 (44% and 46%, respectively), AR (50% and 39%), and PIK3CA (14% and 9%). CDK12 (OR= 8.955, 95% C.I. [2.156, 37.192], p=0.003) and KIT (OR= 5.710, 95% C.I. [1.235, 26.397]. p=0.031) alterations were more frequently detected in African Americans. In terms of pathologic mutation type, frameshift mutations were significantly more frequent in African Americans (OR= 2.293, 95% C.I. [1.103, 4.769], p=0.035). All patients were CRPC at the time of testing and had prior abiraterone and/or enzalutamide, but there were no significant differences between African American and Caucasian patients with regards to prior life-extending therapies. Conclusions: African Americans with CRPC post treatment with abiraterone and/or enzalutamide had a higher frequency of P/LP CDK12 and KIT mutations, which have both been shown to lead to aggressive clinical features and treatment resistance. African Americans also had a higher incidence of frameshift mutations, a finding not previously noted. [Table: see text]

Evaluation of ctDNA in patients with CRPC with pathogenic germline mutations in BRCA2

253

Background: Approximately 3-5% of advanced prostate cancer patients have pathogenic BRCA2 mutations in germline tests. In this study, we examine the relationship between pathogenic germline BRCA2 mutation and somatic changes in ctDNA. Methods: Germline screenings were performed by Invitae multi-cancer gene panel which includes 50-84 genes. ctDNA alterations were detected by Guardant 360 assays which report somatic changes in 70-83 genes. All ctDNA samples were collected in post-abiraterone and/or enzalutamide (in CRPC patients). Any pathogenic/likely pathogenic somatic alterations in the ctDNAs with more than 0.1% of allelic fraction were included in this cohort. The type of mutation detected in ctDNA was also assessed (truncating, point, etc.). Statistical significance for comparison is calculated with Fischer Exact Probablity Test and Chi-Square Test. Results: A total of 11 patients had germline BRCA2 pathogenic mutations and ctDNA assays; 267 patients had no germline DNA pathogenic alterations and ctDNA assays. Compared to germline normal patients, the germline BRCA2 mutations were less likely to have AR alterations on ctDNA (OR=0.2133, 95% C.I. [0.087, 0.525], p-value = 0.0003). BRCA2 germline positive patients were also more likely to have a mutated BRCA1, BRCA2, and TP53 ctDNA (OR=7.899, 95% C.I. [1.2745, 48.9548], p=0.055), (OR=7.899, 95% C.I. [1.7529, 16.059], p=0.008), and (OR=6.442, 95% C.I. [2.449, 16.946], p=0.00001), respectively. All other ctDNA assessed genes were mutated at a similar frequency between germline BRCA2 mutated and “normal” germline patients. BRCA2 germline mutations patients are less likely to have copy number alterations (CNVs) (OR=0.3992, 95% C.I. [0.2168, 0.7352], p=0.0031) and more likely to have frameshift mutations (OR=2.3182, 95% C.I. [1.169, 4.5972], p=0.0183). Conclusions: The ctDNA testing in this CRPC population (after abiraterone and/or enzalutamide) was less likely to find AR alterations and more likely to find pathogenic mutations for BRCA1, BRCA2, and TP53 in BRCA2 germline positive patients. In addition, BRCA2 germline positive CRPC patients were more likely to have frameshift mutations and less likely to have CNVs than those with an intact germline. Characterizing the mutational landscape in BRCA2 germline mutated patients may help to better define underlying disease biology. Those with BRCA mutated germline may be less likely to have AR driven tumors. More study is needed to better understand patients with underlying DNA repair defects.

Pathogenic BRAF mutations in prostate cancer: Frequency and distribution

257

Background: Human cancers are known to harbor mutations in BRAF, a rare but clinically significant finding. BRAF p. V600E is the most common hot spot mutation and has been well described, however other activating mutations are less well studied. Herein we evaluate the landscape of BRAF pathogenic/likely pathogenic (P/LP) variations in prostate cancer patients. Methods: De-identified records from patients with primary prostate cancer who underwent NGS with Tempus xF (ctDNA, 105 genes) or xT (tissue, DNAseq of 648 genes, 500× coverage, full transcriptome RNAseq for a subset of patients) were analyzed from a real-world dataset. Results: There were 5,902 patients identified with prostate cancer who underwent any Tempus xT testing, of whom 85 (1.4%) harbored a P/LP BRAF mutation. Of these 85 patients, the most prevalent BRAF mutation identified was BRAF K601E (Lys601Glu) (36% of total), followed by Gly469Ala (18%) and Leu597Arg (8%, Table) There were 4,177 patients identified with primary prostate cancer who underwent any Tempus xF testing, of whom 50 (1.2%) harbored a P/LP BRAF mutation. Similarly, the most prevalent BRAF mutation identified was BRAF K601E (26%). Conclusions: This study presents the first large-scale genomic characterization of BRAF mutations in patients with prostate cancer using both tissue and ctDNA NGS analysis. Among thousands of samples from prostate cancer patients, K601E was the most common BRAF mutation. This confirms findings of smaller studies and has implications for developmental therapeutics. Further studies should document the natural history of BRAF K601E in prostate cancer. [Table: see text]

Analysis of TP53 gain of function mutations in metastatic castration-resistant prostate cancer

246

Background: TP53, an oncogene implicated in the development of many malignancies, is commonly altered in mCRPC. Gain-of-function mutations in TP53 confer increased oncogenic properties of this gene and play a role in mCRPC. The goal of this study was to characterize somatic TP53 mutations, specifically gain-of-function mutations, in the ctDNA of mCRPC patients in the context of prior therapies. Methods: A retrospective analysis of mCRPC patients at Tulane Cancer Center between 2015-2022 was performed. All patients had ctDNA testing performed with the Guardant360 multigene panel assay. Clinical annotation including initial diagnosis, staging, treatment history, and family history were obtained. TP53 mutations were classified based on existing published functional studies and/or in silico evaluation. Statistical analyses were performed with Fisher's exact and Chi-squared tests where appropriate. Results: 338 mCRPC patients with ctDNA testing were included in this analysis. 76 patients had no prior treatment with either abiraterone or enzalutamide, while 262 patients had been treated with abiraterone and/or enzalutamide. Somatic TP53 mutations were similar in frequency between those with or without abiraterone/enzalutamide pretreatment; 46% (35/76) of patients in the abiraterone/enzalutamide naïve subset had a somatic TP53 mutation, compared to 41% (108/262) of patients previously treated with abiraterone and/or enzalutamide. Only 9% (7/76) of abiraterone/enzalutamide naïve patients had a TP53 gain-of-function mutation, compared to 19% (49/262) of patients previously treated with one or both drugs ( p = 0.05). The most common type of TP53 mutation was loss-of-function. There were no significant associations between TP 53 mutations and occurrence of other common mutations. Conclusions: mCRPC patients with prior treatment of abiraterone and/or enzalutamide were significantly more likely to have a gain-of-function TP53 mutation. Further studies are needed to investigate therapeutic implications of these findings.

68Ga-PSMA-11 patients with newly diagnosed and recurrent prostate cancer (Firefly Study): Preliminary results

54

Background: A primary challenge facing oncologists is the accurate identification of the source of the rising PSA in the recurrent disease setting and the failure of proper staging at the time of initial therapy. PSMA imaging allows for progress in this regard, however access remains an issue. As such, we designed the Firefly study to offer PSMA imaging to patients between May 2021 and May 2022, to better characterize their disease. Methods: This is a phase II expanded access intermediate sized clinical trial using 68Ga-PSMA-11 (Telix Pharma cold kit) under Tulane’s own Investigational New Drug (IND). Clinical trial information: NCT04854369. Two cohorts are utilized, recurrent disease with a PSA > 0.2 or > 2.0 post-radiation, and newly diagnosed high risk or oligo-metastatic patients as assessed by conventional imaging. Between May 2021 and May 2022, a total of 90 patients were enrolled. The study was designed for a maximum of 300 patients but was terminated when access to insurance approved PSMA scans was available. Patients received 1.8–2.2 MBq/kg body weight with 68Ga-PSMA-11 (per EANM guidelines). The lower and upper limits of the dose were set to 3 to 7 mCi respectively. Primary Objective(s): Utilize 68Ga-PSMA-11 PET to define uptake location for localization of prostate cancer metastatic sites in patients prior to initial therapy, and in both local recurrences and metastatic sites in patients with recurrent disease after initial therapy. Secondary Objectives: To assess the therapeutic consequences of 68Ga-PSMA-11 PET/CT imaging in prostate cancer patients with and without prior treatment. Results: Of the 90 patients enrolled 81 were in the recurrent disease cohort and nine had newly diagnosed disease. Of the 81 patients with recurrent disease; 30 were known metastatic and were scanned with the intention of application for expanded access to 177Lu-PSMA-617, 8 received radiation for their oligometastases, 12 received a combination of radiation and initiation of hormone therapy, 13 continued surveillance, 5 were sent for salvage therapy, 13 were treated with novel hormones. Of the 9 patients with newly diagnosed disease all of them were negative for metastasis on conventional imaging. However, when scanned with 68Ga-PSMA-11, 7/9 had a positive PSMA scan. A lesion in the prostate was identified in 2/7 patients, 2/7 were found to have de novo metastatic disease to the lymph nodes and 3/7 were found to have bone metastasis. All these patients were treatment naïve and 5/7 had changes to their planned definitive treatment plan based on these results, as high-risk patients found to have previously unidentified de novo metastatic disease. Conclusions: Further analysis of the data is planned to complete secondary objectives; however, this study demonstrates the potentially meaningful impact of PSMA imaging for patient treatment planning and individualized care. Clinical trial information: NCT04854369 .

CDK12 pathogenic mutations in African American and White patients with prostate cancer

38

Background: African American (AA) men are underrepresented in prostate cancer (PC) trials but have a greater probability of both developing and dying from prostate cancer (PC) than other populations. CDK12 mutations in PC are associated with aggressive disease, increased metastasis, and decreased overall survival. Some preliminary data has suggested that CDK12 mutations may be more common in AA men. This study reports data from next-generation sequencing (NGS) of tissue from a large population of patients with PC in the real-world setting to investigate frequency of pathogenic CDK12 mutations in AA men and White men. Methods: De-identified records from patients with primary PC who underwent NGS with Tempus xT (solid tumor, 648 genes, 500× coverage, full transcriptome RNAseq for a subset of patients) were analyzed to characterize the frequency and types of pathogenic CDK12 mutations, and co-mutation in other assessed genes. Results were compared between patients identified as AA and White. Patients were excluded if they were Microsatellite Instability high (MSI-H), Tumor Mutational Burden (TMB) ≥10, or Mismatch Repair deficient (MMR-d). Results: Genomic profiles were analyzed from tissue samples of 6121 unique patients; of 3,555 patients with known race, 646 (18%) were AA, 2657 (75%) were White, and 252 (7%) were of other races. Of these patients, 3026 were AA or White after excluding 277 patients with known MSI-H, TMB≥10, or MMR-d status. AA were younger at diagnosis than Whites (median 63 vs 66 years; p<0.001). Tissue samples from AA men were significantly more likely than those from Whites to express a pathogenic CDK12 mutation (42 [7.2%] vs 93 [3.8%], p<0.001). The majority of the variants identified were truncating mutations. There were no differences in truncating vs. non-truncating alterations between White and AA men, nor were there differences in the prevalence or distribution of co-mutations between the two populations. Conclusions: AA men with PC show a higher frequency of pathogenic CDK12 mutations than Whites in a large real-world population. Co-mutations did not vary by race, and the alterations were most likely to be truncating mutations in both races.

Genomic alterations in patients with prostate cancer with liver metastases

248

Background: mCRPC patients with liver metastases have a poor prognosis and often progress rapidly on a variety of treatments. Previously, preliminary ctDNA analyses of mCRPC patients with liver metastases showed a range of commonly altered genes in patients with liver metastases (Ranasinghe et al; 2019). In this follow-up, we evaluated ctDNA alterations in an expanded cohort of mCRPC patients with liver metastases. Methods: From Tulane Cancer Center, retrospective review of mCRPC patients was used to identify patients with confirmed liver metastasis. All liver metastases were confirmed based on imaging data. All patients included had ctDNA evaluated with a multi-gene cancer panel via Guardant 360 assay (Guardant Health, Inc). Additional clinical annotation including family history, germline testing, staging, imaging, and laboratory values. Statistical analyses were performed with Fisher’s Exact and Wilcoxon Rank Sum tests. Results: 158 mCRPC patients with appropriate diagnostic imaging as well as ctDNA testing. From this group, 8% (n= 12) had confirmed liver metastases. Among the patients with liver metastasis, the most common alterations detected were in AR (50%; 6/12) and PIK3CA (25%; 3/12). Patients with liver metastasis were more likely to have amplifications in FGFR1 detected in their ctDNA (OR= 14.40; 95% C.I. (1.83, 113.22); p= 0.03). In addition to ctDNA, germline data was assessed, and it was found that patients with liver metastasis were more likely to have a pathogenic germline mutation (OR= 7.61; 95% C.I. (2.85, 20.31); p<.0001). The most common germline mutations detected in patients with liver metastasis were in BRCA2 (n= 3) and TP53 (n= 2). Conclusions: Though liver metastasis are less common in prostate cancer, it often occurs following extensive treatment and results in a poor prognosis for patients. In patients with liver metastasis, FGFR1 amplification was more often detected in ctDNA. Importantly, patients with liver metastasis were significantly more likely to have a pathogenic germline alteration.

Evaluation of ctDNA in patients treated with lutetium-177-PSMA-617

243

Background: Lutetium-177- PSMA-617 (Lu-177) is a radioligand therapy that delivers radiation to PSMA-expressing cells in patients with advanced prostate cancer. In this study, we aimed to analyze ctDNA in responders and non-responders after Lu-177 treatments. Methods: Data was retrospectively collected on 31 heavily pre-treated metastatic CRPC patients who received Lu-177 treatment at Tulane Cancer Center. All patients fulfilled VISION criteria for treatment and all had ctDNA assessment with Guardant 360 within 30 days prior to first treatment with Lu-177. Of the 31 patients, 7 had paired ctDNA assessment both prior initiation of treatment and at the end of treatment. Clinical data such as PSA response (PSA decline 50% or more) to Lu-177, initial diagnosis, pathology, treatment history, and relevant germline genetic data were collected. Results: Of the 31 patients who received Lu-177 treatment, 18 had PSA response to Lu-177 (responders) and 13 did not (non-responders). In ctDNA mutational analyses, there were no significant differences detected prior to treatment between responders and non-responders. There was, however, a significant increase in the presence of copy number amplifications in non-responders (n= 11/13) when compared to responders (n= 7/18) (OR= 8.64, 95% C.I. [1.46, 51.25)], p = 0.0250). Amplification was detected in 10 genes in non-responders, whereas responders only had amplifications in AR (7/18) and EGFR (1/18). The most frequently amplified genes in non-responders were AR (8/13), CCNE1 (6/13), EGFR (4/13), and FGFR1 (4/13). Furthermore, in analysis of the 7 patients with paired ctDNA assessments, amplifications increased during treatment with Lu-177. Conclusions: Radioligand therapy with Lu-177 has been shown to prolong life and reduce disease progression. Our analysis of the cohort of Lu-177 treated patients showed that the presence of gene amplifications in ctDNA may play a role in predicting resistance to treatment with Lu-177.

A Recurrent ADPRHL1 Germline Mutation Activates PARP1 and Confers Prostate Cancer Risk in African American Families

African American (AA) families have the highest risk of prostate cancer. However, the genetic factors contributing to prostate cancer susceptibility in AA families remain poorly understood. We performed whole-exome sequencing of one affected and one unaffected brother in an AA family with hereditary prostate cancer. The novel non-synonymous variants discovered only in the affected individuals were further analyzed in all affected and unaffected men in 20 AA-PC families. Here, we report one rare recurrent ADPRHL1 germline mutation (c.A233T; p.D78V) in four of the 20 families affected by prostate cancer. The mutation co-segregates with prostate cancer in two families and presents in two affected men in the other two families, but was absent in 170 unrelated healthy AA men. Functional characterization of the mutation in benign prostate cells showed aberrant promotion of cell proliferation, whereas expression of the wild-type ADPRHL1 in prostate cancer cells suppressed cell proliferation and oncogenesis. Mechanistically, the ADPRHL1 mutant activates PARP1, leading to an increased H2O2 or cisplatin-induced DNA damage response for prostate cancer cell survival. Indeed, the PARP1 inhibitor, olaparib, suppresses prostate cancer cell survival induced by mutant ADPRHL1. Given that the expression levels of ADPRHL1 are significantly high in normal prostate tissues and reduce stepwise as Gleason scores increase in tumors, our findings provide genetic, biochemical, and clinicopathological evidence that ADPRHL1 is a tumor suppressor in prostate tissue. A loss of function mutation in ADPRHL1 induces prostate tumorigenesis and confers prostate cancer susceptibility in high-risk AA families.

IMPLICATIONS

This study highlights a potential strategy for ADPRHL1 mutation detection in prostate cancer-risk assessment and a potential therapeutic application for individuals with prostate cancer in AA families.

Inherited TP53 Variants and Risk of Prostate Cancer

BACKGROUND

Inherited germline TP53 pathogenic and likely pathogenic variants (gTP53) cause autosomal dominant multicancer predisposition including Li-Fraumeni syndrome (LFS). However, there is no known association of prostate cancer with gTP53.

OBJECTIVE

To determine whether gTP53 predisposes to prostate cancer.

DESIGN, SETTING, AND PARTICIPANTS

This multi-institutional retrospective study characterizes prostate cancer incidence in a cohort of LFS males and gTP53 prevalence in a prostate cancer cohort.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We evaluated the spectrum of gTP53 variants and clinical features associated with prostate cancer.

RESULTS AND LIMITATIONS

We identified 31 prostate cancer cases among 163 adult LFS males, including 26 of 54 aged ≥50 yr. Among 117 LFS males without prostate cancer at the time of genetic testing, six were diagnosed with prostate cancer over a median (interquartile range [IQR]) of 3.0 (1.3-7.2) yr of follow-up, a 25-fold increased risk (95% confidence interval [CI] 9.2-55; p < 0.0001). We identified gTP53 in 38 of 6850 males (0.6%) in the prostate cancer cohort, a relative risk 9.1-fold higher than that of population controls (95% CI 6.2-14; p < 0.0001; gnomAD). We observed hotspots at the sites of attenuated variants not associated with classic LFS. Two-thirds of available gTP53 prostate tumors had somatic inactivation of the second TP53 allele. Among gTP53 prostate cancer cases in this study, the median age at diagnosis was 56 (IQR: 51-62) yr, 44% had Gleason ≥8 tumors, and 29% had advanced disease at diagnosis.

CONCLUSIONS

Complementary analyses of prostate cancer incidence in LFS males and gTP53 prevalence in prostate cancer cohorts suggest that gTP53 predisposes to aggressive prostate cancer. Prostate cancer should be considered as part of LFS screening protocols and TP53 considered in germline prostate cancer susceptibility testing.

PATIENT SUMMARY

Inherited pathogenic variants in the TP53 gene are likely to predispose men to aggressive prostate cancer.

Liquid biopsy AR/enhancer alteration detection before AR-targeted therapy and correlation with survival in metastatic castrate-resistant prostate cancer patients

171

Background: Patients with metastatic castrate-resistant prostate cancer (mCRPC) have a variety of different systemic therapy options, yet survival outcomes remain poor. To minimize the chance of rapid resistance, it is critical to be able to personalize therapy upfront. We previously developed a cell-free DNA liquid biopsy assay that tracks alterations in the androgen receptor ( AR) locus, including its upstream enhancer (EnhanceAR-Seq). This assay demonstrated the ability to stratify patients based on resistance to AR-directed agents after treatment started (Dang and Chauhan et al., JCO PO, 2020). Here we evaluated if the same approach can accurately risk-stratify patients with mCRPC prior to the initiation of first-line AR-targeted therapy. Methods: We performed EnhanceAR-Seq on plasma cell-free DNA samples from 55 mCRPC patients prior to the initiation of AR-targeted therapy. Forty-seven patients were treated with Abiraterone and eight with Enzalutamide. Five patients were excluded due to having already received AR-targeted therapy or being lost to follow-up. Kaplan-Meier analysis was performed, and progression-free survival (PFS) and overall survival (OS) were assessed in relation to AR/enhancer locus status (wild-type vs. altered). Results: Median follow-up time was 30 months. EnhanceAR-Seq noninvasively detected AR/enhancer locus alterations in 36% (18/50) of the patients in our cohort, while 64% (32/50) were determined to be wild-type. Alterations detected by the assay were AR amplification (12/18), AR nonsynonymous single nucleotide variants (4/18), AR truncation (2/18), and AR enhancer amplification (13/18). Eleven patients had both AR gene body and enhancer amplifications present. Strikingly, patients with AR/enhancer alterations detected in plasma cell-free DNA were found to have significantly worse outcomes, with median PFS of 16.3 (wild-type) vs. 10.8 months (altered) (p = 0.046; HR = 2.10), and OS trending toward significantly different with median 34.3 (wild type) vs. 24.7 months (altered) (p = 0.19; HR = 1.05). Conclusions: AR/enhancer locus alterations in patients with mCRPC, as detected noninvasively by EnhanceAR-Seq, corresponded with significantly worse PFS and trended toward significantly worse OS. Our results support the role of cell-free DNA AR/enhancer locus alterations as prognostic, and potentially predictive, biomarkers that enable more precise upfront risk stratification and treatment personalization.

Comparative ctDNA analyses of African-American and Caucasian patients with CRPC

24

Background: Somatic genetic analyses have indicated genetic distinctions in AA as compared to C patients. In the Mahal et al. study (1) evaluating a broad spectrum of pts with tissue based assays, FOXA1 mutations were more frequent in AA men and TP53 mutations were less frequent in AA men as compared to C men. In a separate analysis by Khashab et al. (2) conducted in prostate cancer pts receiving androgen deprivation therapy, using both tissue and ctDNA assays, the authors reported AR, TP53, SPOP, and BRCA2 were more frequently mutated in AA men as compared to C men. Herein we assessed the Guardant 360 platform in assessing ctDNA differences in AA and C men, all of whom had CRPC at the time assays were performed. Methods: Guardant 360 was used to analyze ctDNA with a cut-off of >0.5% for allelic fractions for ascertaining the presence or absence of pathogenic mutations and various amplifications. Lower allelic fractions were not analyzed given these may represent less relevant mutations. Depending on the timing of the assays (2015-2021), 70-83 genes were analyzed. All pts had CRPC and all patients were treated at Tulane Cancer Center. Chi Square analyses were used to determine statistical differences. AR, BRCA2, and TP53 were assessed but SPOP and FOXA1 were not assessable in the Guardant ctDNA assay. Both mutations and amplifications were evaluated. Results: Among men with CRPC, a total of 48 AA men and 179 C men were analyzed using ctDNA. Clear distinctions were found in the alteration reported in APC, TP53, and CDK12. TP53 was less frequently mutated and other genes were more frequently altered in the AA men. Conclusions: Using Guardant ctDNA assays in men with CRPC, clear distinctions were found in AA men as compared to C men. It is unclear why these results differ from that reported by others, however distinctions in both the assays and the populations are notable.[Table: see text]

Longitudinal ctDNA alterations in germline positive CRPC patients

275

Background: Circulating tumor-derived DNA (ctDNA) is an accessible method for characterizing somatic alterations. We report longitudinal ctDNA screenings of mCRPC patients (pts) who have had germline testing. Methods: Patients with both germline testing and ctDNA assessment were included. Germline testing was performed with a multi-gene cancer panel from Invitae (50-83 genes) and somatic alterations in ctDNA were identified by testing with Guardant 360 (70-83 genes). ctDNA alterations were characterized as deletions, frameshift, missense, nonsense, and other mutations. A total of 177 patients in various stages of therapy had both ctDNA and germline DNA tested. Results: From 2015-2021, 177 mCRPC patients were included and had an average of 3 ctDNA tests. 11.3% (20/177) had pathogenic or likely-pathogenic germline mutations. The common pathogenic germline mutations were in BRCA2 (25%; 5/20), ATM (10%; 2/20), and MSH2 (10%; 2/20). In ctDNA, missense mutations were the most prevalent type of gene alteration in germline negative (n = 539/790, 68%) and germline positive (n = 124/218, 57%) followed by frameshift mutations at 22% (n = 48/218) in germline positive and 10% (n = 80/790) in germline negative patients. Germline positive patients were more likely to have somatic frameshift mutations (OR = 2.09, 95% C.I. (1.3792, 3.1618), p = 0.001) and less likely to have missense mutations (OR = 0.61, 95% C.I. (0.4519, 0.8351), p = 0.002). Other alterations including deletions, nonsense, and other mutations were not significantly different. Of the germline positive pts, BRCA2 mutation was associated with the highest number of somatic alterations. Conclusions: Germline positive CRPC patients were more likely to have frameshift mutations and less likely to missense mutations compared to germline negative CRPC patients. Patients with germline mutations in BRCA2 and TP53 had the highest number of somatic alterations detected in ctDNA over the course of ctDNA evaluation.

Evaluation of ctDNA alterations in mCRPC patients with germline pathogenic mutations

177

Background: Germline alterations are found in approximately 12-17% of CRPC patients. Similarly, evaluating tumoral changes with circulating tumor DNA (ctDNA) has become an increasingly useful tool for understanding mechanisms underpinning disease progression. In this study, we evaluated both germline and somatic genetic changes in patients with mCRPC. Methods: Patients included had germline screening and ctDNA analyzed with the Guardant 360 assay. All patients were CRPC at the time of Guardant testing. Germline alterations were classified as pathogenic/likely-pathogenic or not pathogenic. Only ctDNA alterations with an alleleic fraction greater than 0.5% were included in analyses. Additional evaluation of CRPC status, treatment history, family history and other clinical covariates are ongoing. Chi-square and Fischer’s Exact tests were used for comparison of cohorts. Results: A total of 168 Caucasian CRPC patients had Guardant 360 testing at time of progression and germline testing between 2015-2021. 61% (n = 102/168) of patients have previously had treatment with abiraterone, 49% (n = 82/168) have had Enzalutamide and 40% (n = 68/168) have had treatment with taxanes. 12% (n = 20/168) of CRPC patients had a pathogenic/likely-pathogenic (P/LPv) germline alteration, 46% (n = 77/168) had a germline variant of unknown significance (VUS), 42% (n = 71/168) were germline negative. CRPC patients with pathogenic germline mutations were significantly more likely to have subsequent somatic alterations in BRCA2 (OR = 5.05, 95% C.I. (1.11, 23.01), p = 0.055), NF1 (OR = 7.89, 95% C.I. (2.15, 28.10), p = 0.004), and TP53 (OR = 3.52, 95% C.I. (1.28, 9.68), p = 0.015). In TP53, among germline positive patients, 45% (n = 9/20) had TP53 alterations compared to 30% (n = 45/148) of germline negative patients. Conclusions: Germline positive (P/LPv) CRPC patients were significantly more likely to have somatic alterations in BRCA2, NF1, and TP53. Understanding the totality of genetic changes, both germline and acquired somatic alterations is essential as the arsenal of targeted treatment for CRPC continues to expand. Additional studies including longitudinal assessment genetic changes and clinical correlates will be necessary to evaluate these findings in the context of treatment outcomes and disease progression.

Circulating tumor DNA responses to high-dose testosterone injections in CRPC patients

173

Background: Some proportion of men with CRPC have favorable responses to high doses of testosterone (HDT) and some do not. Genomic determinants of these responders and non-responders are poorly understood. Herein ctDNA predictors of response are assessed using a responder/non-responder analysis. Methods: All men with CRPC had been pretreated with abiraterone, enzalutamide, or both. A ctDNA test was obtained prior to high doses of testosterone (administered as a dose of 400 mg IM testosterone cypionate every 3-4 weeks). Guardant 360 was used to analyze ctDNA (with an allelic fraction cut-off of > 0.5%) to ascertain the presence or absence of pathogenic mutations. Lower allelic fractions were not analyzed. Responders had a PSA decline of 50% or more (N = 16), non-responders received at least two doses of testosterone but never had any PSA decline at all (N = 20). All patients were treated at Tulane Cancer Center. Results: AR amplifications were more commonly detected (p = 0.036) pre-treatment in the ctDNA of responders (5/16) as compared to non-responders (1/20). No differences were found in those with common AR mutations; T878A was detected in 2/16 responders and 2/20 non-responders, L702H was detected in 1/16 responders and 2/20 non-responders. No differences were seen with regard to TP53 mutations, 6/20 non-responders and 7/16 responders. Non- AR/non- TP53 mutations were not distinct in the two groups but trended (P = 0.15) toward being more common in non-responders (5/16 in responders versus 11/20 non-responders). Pre- and post- ctDNA analyses were conducted in 5/6 patients for those with AR amplification at baseline. In all 5 of these patients, the degree of AR amplification diminished after testosterone injections. Conclusions: In this analysis of CRPC patients who were responders and non-responders to 400 mg testosterone cypionate q 3-4 weeks (post-abiraterone and/or enzalutamide), only AR amplifications in ctDNA were predictive of response. In all measured patients, the degree of AR amplification in the ctDNA diminished after testosterone injections.

Efficacy of systemic therapies in men with metastatic castration resistant prostate cancer harboring germline ATM versus BRCA2 mutations

BACKGROUND

Among men with metastatic prostate cancer, about 10% have germline alterations in DNA damage response genes. Most studies have examined BRCA2 alone or an aggregate of BRCA1/2 and ATM. Emerging data suggest that ATM mutations may have distinct biology and warrant individual evaluation. The objective of this study is to determine whether response to prostate cancer systemic therapies differs between men with germline mutations in ATM (gATM) and BRCA2 (gBRCA2).

METHODS

This is an international multicenter retrospective matched cohort study of men with prostate cancer harboring gATM or gBRCA2. PSA₅₀ response (≥50% decline in prostate-specific antigen) was compared using Fisher's exact test.

RESULTS AND LIMITATIONS

The study included 45 gATM and 45 gBRCA2 patients, matched on stage and year of germline testing. Patients with gATM and gBRCA2 had similar age, Gleason grade, and PSA at diagnosis. We did not observe differences in PSA₅₀ responses to abiraterone, enzalutamide, or docetaxel in metastatic castration resistant prostate cancer between the two groups; however, 0/7 with gATM and 12/14 with gBRCA2 achieved PSA₅₀ response to PARPi (p < .001). Median (95% confidence interval) overall survival from diagnosis to death was 10.9 years (9.5-not reached) versus 9.9 years (7.1-not reached, p = .07) for the gATM and gBRCA2 cohorts, respectively. Limitations include the retrospective design and lack of mutation zygosity data.

CONCLUSIONS

Conventional therapies can be effective in gATM carriers and should be considered before PARPi, which shows limited efficacy in this group. Men with gATM mutations warrant prioritization for novel treatment strategies.

Abstract 550: Cell-free DNA alterations in the AR/enhancer locus measured before AR signaling inhibition portend poor overall survival in metastatic castration resistant prostate cancer patients

Background: We previously developed a liquid biopsy assay called Enhancer and neighboring loci of Androgen Receptor Sequencing (EnhanceAR-Seq) (Dang & Chauhan et al, JCO PO, 2020). We applied it to a heterogeneous cohort of metastatic prostate cancer patients after the start of AR-directed therapy, and showed that alterations in the AR locus were associated with worse survival. Here we asked if AR/enhancer genomic alterations detected in plasma cell-free DNA prior to the administration of first-line AR-selective inhibitors (ARSIs) can predict survival in metastatic castration resistant prostate cancer (mCRPC) patients.

Methods: We applied EnhanceAR-Seq to plasma cell-free DNA isolated from 20 mCRPC patients from Tulane University collected between April 2015 and June 2017. Assay results were correlated with patient overall survival (OS) and progression-free survival (PFS) from the time of blood collection.

Results: Median follow up time was 32 months. Seventeen patients had blood plasma analyzed before first-line ARSI treatment, while three patients had received prior ARSI treatment before blood collection. EnhanceAR-Seq revealed that the most frequent genomic events detected were AR/enhancer alterations (copy number gain, tandem duplication or missense mutations) in 9 patients (45%), of which 5 patients had both AR gene body and enhancer copy number gain. The other 4 patients each had a single genomic event detected by EnhanceAR-Seq: AR amplification, AR enhancer amplification, AR and AR enhancer tandem duplication, and AR W742C single nucleotide variation. Cell-free DNA-detected alterations in the full AR locus including the AR enhancer were highly significant for inferior OS (P = 0.0009; HR = 17.0) but not for PFS (P = 0.2; HR = 2.2) by Kaplan-Meier analysis across all 20 patients. Subset analysis of the 17 patients with plasma analyzed prior to first-line ARSI treatment revealed that AR/enhancer alterations again predicted significantly worse OS with a median survival of 16.1 months vs. not-reached (P = 0.0009; HR = 14.1).

Conclusions: AR locus alterations detected by EnhanceAR-seq in plasma cell-free DNA collected prior to ARSI administration correlated with significantly worse overall survival in patients with mCRPC. If corroborated, our results suggest that AR/enhancer genomic alterations represent a potent pre-treatment prognostic biomarker in mCRPC patients.

Citation Format: Pradeep Singh Chauhan, Steven H. Hartman, Ha X. Dang, Jace Webster, Haley Ellis, Wenjia Feng, Peter K. Harris, Elisa M. Ledet, Ellen B. Jaeger, Patrick J. Miller, Sydney A. Caputo, Russell K. Pachynski, Oliver Sartor, Christopher A. Maher, Aadel A. Chaudhuri. Cell-free DNA alterations in the AR/enhancer locus measured before AR signaling inhibition portend poor overall survival in metastatic castration resistant prostate cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 550.

Abstract 577: A unified pipeline to detect small mutations, structural variations and copy number alterations from targeted cell-free DNA sequencing in cancer

Introduction: Analysis of cell-free DNA (cfDNA) has recently emerged as a non-invasive modality for guiding cancer diagnostics and treatment decisions. However, efforts have predominantly focused on the analysis of single nucleotide variants (SNVs) and insertions/deletions (indels). Despite the clinical significance of many larger variants such as structural variations (SVs) and copy number alterations (CNAs), detecting them in cfDNA remains a challenge. Given the lack of existing tools we seek to develop an integrated bioinformatic pipeline for SV and CNA detection in cfDNA following targeted hybrid-capture next-generation sequencing (NGS), along with standard SNV and indel analysis.

Methods: SVs were first detected using Manta, Lumpy and Delly in plasma cfDNA in comparison with matched peripheral blood leukocyte (PBL) DNA samples from cancer patients, then combined to identify consensus SVs and genotyped throughout samples from patients and healthy individuals. Next, consensus SVs were called somatic events if they were supported by split reads and discordant read pairs in cfDNA samples from patients but not in matched PBL or healthy donor cfDNA samples. For CNA analysis, the ratio of read depth between patient-derived plasma cfDNA and a panel of healthy controls was calculated across genomic bins using the CNVkit tool, followed by bias correction and recentralization using CNA negative control genes to account for read coverage imbalances in targeted NGS. Last, SNV and indel analysis was integrated from the CAPP-Seq pipeline.

Results: We applied our pipeline to targeted hybrid-capture NGS data from 48 patients across two independent cohorts of metastatic castration resistant prostate cancer (mCRPC). The targeted panel covered the full-length AR gene body and a hotspot region of TMPRSS2-ERG fusion break points. Consistent with earlier whole genome studies, we confirmed known CNAs and SVs in tumor suppressors, oncogenes and regulatory elements including AR gene and AR enhancer duplications (22/48, 46% of patients), TMPRSS2-ERG gene fusions (9/48, 19%), PTEN and TP53 loss (8/48, 17%). Notably, our pipeline outperformed FACTERA which did not detect any TMPRSS2-ERG gene fusions or AR/enhancer tandem duplications. Subsequent analysis showed high concordance between plasma cfDNA and matched tumor biopsies, and our pipeline recapitulated the landscape of SVs and CNAs in an in silico cfDNA simulation from tumor biopsies. Finally, we showed that alterations of the AR/enhancer locus detected by our pipeline were strongly associated with treatment resistance, patient progression-free and overall survival in mCRPC.

Conclusion: We developed a unified pipeline for detection of SVs, CNAs and small mutations in cfDNA targeted sequencing with potential applications in monitoring cancer progression and predicting patient treatment response.

Citation Format: Ha X. Dang, Jace Webster, Pradeep S. Chauhan, Steven H. Hartman, Wenjia Feng, Elisa M. Ledet, Haley Ellis, Patrick J. Miller, Ellen B. Jaeger, Sydney A. Caputo, Peter K. Harris, A. Oliver Sartor, Russell K. Pachynski, Aadel A. Chaudhuri, Christopher A. Maher. A unified pipeline to detect small mutations, structural variations and copy number alterations from targeted cell-free DNA sequencing in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 577.

Comparison of germline mutations in African American and Caucasian men with metastatic prostate cancer

BACKGROUND

The goal of this study is to evaluate germline genetic variants in African American men with metastatic prostate cancer as compared to those in Caucasian men with metastatic prostate cancer in an effort to understand the role of genetic factors in these populations.

METHODS

African American and Caucasian men with metastatic prostate cancer who had germline testing using multigene panels were used to generate comparisons. Germline genetic results, clinical parameters, and family histories between the two populations were analyzed.

RESULTS

A total of 867 patients were included in this retrospective study, including 188 African American and 669 Caucasian patients. There was no significant difference in the likelihood of a pathogenic or likely-pathogenic variants (PV/LPVs) between African American and Caucasian patients (p = .09). African American patients were more likely to have a variant of unknown significance than Caucasians (odds ratio [OR] = 1.95; p < .0001). BRCA1 PV/LPVs were higher in African Americans (OR = 4.86; p = .04). African American patients were less likely to have a PV/LPV in non-BRCA DNA repair genes (OR = 0.30; p = .008). Family history of breast (OR = 2.09; p = .002) or ovarian cancer (OR = 2.33; p = .04) predicted PV/LPVs in Caucasians but not African-Americans. This underscores the limitations of family history in AA men and the importance of personal history to guide germline testing in AA men.

CONCLUSIONS

In metastatic prostate cancer patients, PV/LPVs of tested genes did not vary by race, BRCA1 PV/LPVs were more common in the African American subset. However, PV/LPVs in non-BRCA DNA repair genes were less likely to be encountered in African Americans. Family history associated with genetic testing results in Caucasians only.

Family history and pathogenic/likely pathogenic germline variants in prostate cancer patients

BACKGROUND

Recent literature highlights the importance of germline genetic testing in prostate cancer (PCa) patients. Surprisingly, a literature review indicates that family history (FH) records are incomplete in the major published studies from prostate cancer patients.

METHODS

Prospective family history data were gathered from 496 men in a single institution with a personal history of PCa who underwent germline genetic testing using a panel of at least 79 genes. Comprehensive first degree FH were obtained in all PCa of patients and analysis of prevalent FH was assessed at the time of sample collection.

RESULTS

Pathogenic/likely pathogenic variants (PV/LPVs) were not associated with age at diagnosis, race, or presence of metastasis. One or more first degree relatives (FDR) with any cancer was not predictive for germline PV/LPVs for men with PCa (p = .96). Separate analysis of patients with one or more FDR with breast, prostate, ovarian, or pancreatic cancer revealed that only FDR with breast or ovarian cancer was predictive for PV/LPVs (p = .028, p = .015 respectively). Patients with a FDR with breast cancer had 1.8 increased risk of PV/LPVs, and patients with a FDR with ovarian cancer had 2.9 increased risk of PV/LPV.

CONCLUSION

In men with a personal history of PCa, germline PV/LPVs were associated with a FDR with breast or ovarian cancer. Notably having FDRs with PCa does not predict for PV/LPVs. These data emphasize the contribution of FH in a data set with complete ascertainment of FH.

Comprehensive Analysis of AR Alterations in Circulating Tumor DNA from Patients with Advanced Prostate Cancer

BACKGROUND

Somatic alterations in circulating tumor DNA (ctDNA) may be associated with treatment response or prognosis in prostate cancer (PCa). The goal was to characterize androgen receptor gene (AR) amplifications and mutations detected in ctDNA from patients with PCa and to further understand the somatic genetic heterogeneity of advanced prostate cancer.

PATIENTS AND METHODS

This study included a heterogeneous group of 892 patients with advanced PCa (predominantly castrate-resistant prostate cancer) with AR alterations detected in ctDNA that underwent next-generation sequencing of 54 to 73 genes via Guardant360 testing (Guardant Health, Inc., Redwood City, CA). Distribution and summary of AR alterations detected, the association of AR alterations with other genes, and a pathway analysis are reported.

RESULTS

The median absolute plasma copy number of AR amplifications was 3.3 (range, 1.2-165.2). Many patients had multiple AR mutations; a total of 112 unique mutations were identified in AR, including L702H (25%), T878A (14%), H875Y (11%), W742C (8%), W742L (4%), F877L (2%), and T878S (2%). Other ctDNA gene alterations in the Guardant assays included TP53 (50%), MYC (34%), BRAF (32%), PIK3CA (29%), MET (25%), CDK6 (26%), EGFR (24%), FGFR1 (21%), and APC (12%). Many of these non-AR alterations are not tissue verified in other studies. AR amplification cosegregated with alterations in MYC (p < .001), BRAF (p < .001), PIK3CA (p < .001), MET (p < .001), CDK6 (p < .001), EGFR (p < .001), FGFR1 (p = .391), and more. Alterations in APC were significantly associated with mutations in AR (p < .001).

CONCLUSION

Several AR alterations and concomitant non-AR alterations that associate with drug resistance were detected. These findings provide additional insights into the heterogeneity of advanced prostate cancer.

IMPLICATIONS FOR PRACTICE

The goal was to characterize androgen receptor gene (AR) amplifications and mutations detected in circulating tumor DNA (ctDNA) from patients with prostate cancer in relation to non-AR gene alterations detected in the ctDNA landscape. The study included 892 patients with prostate cancer with AR alterations in ctDNA. AR alterations were significantly associated with other gene alterations detected in ctDNA. The common AR mutations found are linked to resistance to abiraterone, enzalutamide, or bicalutamide. Characterization of the circulating AR landscape and gene alterations provides potential additional insight into the somatic genetic heterogeneity of advanced prostate cancer.

Germline BLM mutations and metastatic prostate cancer

BACKGROUND

Biallelic loss-of-function BLM mutations result in Bloom syndrome: a genetic disorder characterized by growth deficiencies, photosensitivity, and multiple cancer susceptibilities. There are conflicting reports about whether or not heterozygous BLM carriers are at a higher risk of various cancers. Without BLM protein functionality, there is evidence of increased sister chromatid exchange and chromosomal instability.

METHODS

Metastatic prostate cancer patients (N = 796) underwent germline genetic testing as part of routine care at three academic centers. Patients with heterozygous BLM mutations were identified. Tumor tissue was analyzed for somatic alterations in those patients who had a germline pathogenic mutation. Control data using a population sample were extracted from the Genome Aggregation Database.

RESULTS

Heterozygous BLM germline mutations in 5 of 796 patients (prevalence, 0.63%). All mutations were loss-of-function truncating alterations. None of the mutations were BLM^Ash . The control population (gnomAD) frequency of pathogenic or likely pathogenic BLM mutations was 0.18% (212 of 116 653). The relative risk (RR) of BLM mutations in metastatic prostate cancer patients was 3.4 (95% CI, 1.42-8.33; P < .0062) compared to gnomAD controls. Tumor DNA sequencing in the BLM carriers showed no evidence of somatic BLM mutations. Interestingly, 3 of 5 BLM germline carriers had bi-allelic BRCA2 inactivation evident on tumor sequencing. One patient had both germline and somatic mutations in BRCA2. Excluding the patient with the germline BRCA2 mutation (BLM prevalence, 4 of 796: 0.50%) still yielded a statistically significant finding vs the gnomAD controls (RR, 2.8; 95% CI, 1.02-7.39; P < .04).

CONCLUSION

Truncating BLM germline mutations occur at a higher frequency in patients with advanced prostate cancer as compared to control populations. Though no biallelic loss of BLM was no noted in cancers, a surprising number of the BLM germline heterozygotes had pathogenic BRCA2 mutations in their tumor.

TP53 Gain-of-Function Mutations in Circulating Tumor DNA in Men With Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

Circulating tumor DNA (ctDNA), which can be assessed by liquid biopsy, can provide valuable genomic information that may affect treatment response in prostate cancer. The aim of this study was to characterize TP53 mutations and treatment history in prostate cancer.

PATIENTS AND METHODS

This study included 143 patients with metastatic castration-resistant prostate cancer who had undergone ctDNA sequencing via Guardant360 testing. The presence or absence of TP53 mutations was analyzed along with treatment history for this group. TP53 mutations were further classified as gain of function (GOF) or not GOF, and analyzed with prior therapies.

RESULTS

Chi-square analysis was performed for treatment history and TP53 status (further specified as all TP53 mutations or only TP53 GOF mutations). There were no associations between prior receipt of abiraterone/enzalutamide therapy and all TP53 mutations, or between docetaxel therapy and all TP53 mutations. However, TP53 GOF mutations had a positive association with prior abiraterone/enzalutamide therapy (P = .047). There was no association of TP53 GOF mutations with prior docetaxel therapy. The most frequent alterations co-occurring with all TP53 mutations were in AR, BRAF, EGFR, MYC, and PIK3CA. Common coalterations with TP53 GOF mutations included AR, BRAF, EGFR, RB1, NF1, and PIK3CA. There was an association of RB1 mutations with TP53 GOF mutations, versus RB1 mutations and no TP53 GOF mutations (P = .0036).

CONCLUSION

TP53 GOF mutations may provide a valuable pathway to delineate metastatic castration-resistant prostate cancer TP53 mutations into therapeutic categories. Association with disease progression while receiving abiraterone/enzalutamide therapy was apparent in this study; however, further studies are needed to elaborate the therapeutic and prognostic implications.

Circulating tumor DNA alterations in patients with metastatic castration-resistant prostate cancer

BACKGROUND

Because cell-free DNA (cfDNA) analysis facilitates the noninvasive genomic profiling of metastatic castration-resistant prostate cancer (mCRPC), the authors evaluated the association between cfDNA alterations and outcomes and evolution with therapy.

METHODS

Patients with mCRPC underwent cfDNA genomic profiling using Guardant360, which examines major cancer-associated genes. Clinical factors, therapy information, failure-free survival, and overall survival (OS) were obtained for select patients. The association between genomic alterations and outcomes was investigated.

RESULTS

Of 514 men with mCRPC, 482 (94%) had ≥1 circulating tumor DNA (ctDNA) alteration. The most common recurrent somatic mutations were in TP53 (36%), androgen receptor (AR) (22%), adenomatous polyposis coli (APC) (10%), neurofibromin 1 (NF1) (9%), epidermal growth factor receptor (EGFR), catenin beta-1 (CTNNB1), and AT-rich interactive domain-containing protein 1A (ARID1A) (6% each); and BRCA1, BRCA2, and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) (5% each) The most common genes with increased copy numbers were AR (30%), MYC (20%), and BRAF (18%). Clinical outcomes were available for 163 patients, 46 of whom (28.8%) were untreated for mCRPC. A higher number of ctDNA alterations, AR alterations, and amplifications of MYC and BRAF were associated with worse failure-free survival and/or OS. On multivariable analysis, MYC amplification remained significantly associated with OS. Prior therapy and serial profiling demonstrated the evolution of alterations in AR and other genes.

CONCLUSIONS

ctDNA frequently was detected in this large cohort of "real-world" patients with mCRPC, and the alterations appeared to be similar to previously reported tumor tissue alterations. A higher number of alterations, and AR and MYC alterations, appear to compromise clinical outcomes, suggesting a role for immune checkpoint inhibitors and novel AR and BET inhibitors in selected patients.

Laboratory-Based Biomarkers and Liver Metastases in Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

Metastatic castrate-resistant prostate cancer (mCRPC) patients with liver metastases have a poor prognosis. No large studies have investigated the clinical and biochemical parameters associated with liver metastases in this population.

MATERIALS AND METHODS

Patient data made available via Project Data Sphere were collected from 1,281 men with mCRPC who were enrolled on to three phase III clinical trials for the treatment of their disease. Multiple logistic regression was performed on eight clinical and biochemical baseline variables to test their association with the presence of liver metastases on baseline radiographic imaging. Variables of interest included prior docetaxel exposure, Eastern Cooperative Oncology Group performance status, albumin, alkaline phosphatase, alanine transaminase, aspartate transaminase (AST), hemoglobin (HGB), lactate dehydrogenase (LDH), prostate-specific antigen, and total bilirubin. Final models were compared when treating the variables as either continuous or categorized.

RESULTS

Multiple variable analysis demonstrated that an increasing serum AST or LDH or a decreasing HGB was associated with an increased probability of having documented radiographic liver metastases (p < .0001). The area under the curve for the continuous model was 0.6842 and 0.6890 for the categorical one, with the latter model containing a dichotomized AST and LDH based on the upper limit of normal and tertile ranges of HGB based on the distribution of the outcome.

CONCLUSION

Our analysis demonstrated a significant association between the presence of liver metastases and laboratory levels of AST, LDH, and HGB. These have implications for patient management. More research is needed to validate these biomarkers and prospectively determine their application in the clinical setting.

IMPLICATIONS FOR PRACTICE

The purpose of this study was to evaluate biochemical and clinical biomarkers associated with the presence of liver metastases in men diagnosed with metastatic castrate-resistant prostate cancer. The results indicate that quantitative assessments of aspartate transaminase, lactate dehydrogenase, and hemoglobin are significantly associated with an increased probability of having documented radiographic liver metastases. Analysis of these simple variables can alert clinicians to those at high risk for prostate cancer that has spread to the liver, a finding of clear importance for clinical management.

Germline variants and family history in caucasian and African-American prostate cancer

e16548

Background: Family history (FH) is a well-documented risk factor for prostate cancer (PCa). Previously, germline pathogenic variants (PVs) have been identified in metastatic PCa. The goal of this study was to fully evaluate cancer FH and assess PVs detected in PCa patients undergoing both detailed FH ascertainment and germline genetic testing. Methods: FHs were collected from 535 PCa pts (Caucasian (Ca) n = 359, African American (AA) n = 85, Other n = 18) at Tulane from 2015-2016. Age at diagnosis, Gleasons, and the presence of metastases at any time were noted for these pts. Chi-square and the Mann-Whitney U tests were performed to identify relationships between clinical parameters and FH. 124 PCa pts including those with both localized and metastatic disease were identified with FHs that met guidelines for genetic testing. Genetic testing was done using a commercially available panel (Invitae, San Francisco, CA) of 25-79 cancer-related genes for mutations/selected exon deletions/duplications. Results: Of the 124 tested pts, 20 pts (16.1%) had ≥ 1 germline PV and 47 pts (37.9%) had ≥ 1 germline variant unknown significance. PVs included: BRCA2 (n = 4), BRCA1 (n = 3), CHEK2 (n = 3), MUTYH (n = 3), ATM (n = 2), TP53 (n = 1), MITF (n = 1), NBN (n = 1), PMS2 (n = 1), and RAD51D (n = 1). No PVs were detected in AA pts (n = 20). 435 of 535 PCa pts (81.3%) had a cancer FH with prostate (37.8%), breast (28.2%), lung (16.4%), colorectal (14.8%), and pancreatic (7.5%) cancer being most common. 281 pts (52.5%) had ≥ 2 relatives with cancer. Pts with PCa FH were more likely to be dx age ≤ 55 (p = 0.017). Median age was younger at dx for pts with PCa FH (p = 0.0005). PCa FH did not alter Gleason or metastatic rate. FH influenced age at dx for Ca men (p = 0.0009, 58 vs. 62.5 and Ca men with PCa FH) were 1.55x more likely to develop metastases (p = 0.035). In AA pts, there were no significant associations between FH, and metastases or age at dx. Conclusions: The most prevalent germline mutations in this cohort were in DNA repair pathway genes. Pts with PCa FH were younger at dx than those without PCa FH. Further studies are needed to understand the co-segregation of PCa with other cancers and genetic studies are needed to clarify the mechanisms of these trends which may differ between Ca and AA men.

Taste and prostate cancer: Preliminary data on a novel patient-reported outcomes

201

Background: Taste alterations are a common yet frequently under-assessed problem in cancer patients. Health-related quality-of-life (HRQOL) instruments for prostate cancer (PCa) patients (pts) do not assess taste despite these hypothetically being related to both appetite and weight loss. Herein we begin to assess taste using a novel instrument evaluating taste alterations with a focus on PCa. Methods: 61 PCa pts treated at Tulane Cancer Center were enrolled in this prospective study. An 18-item questionnaire assessed appetite, taste, smell, and diet. 127 questionnaires were completed (mean 2.1 responses/pt). In a subset of questionnaires, we compared self-reported taste, appetite, and weight loss over a 6-month period. In another subset, we compared taste and appetite to treatments with abiraterone, docetaxel, or enzalutamide. Non-parametric testing was performed. Results: Of the 61 participants with PCa, 18.0% reported poor taste, 17.1% reported poor appetite, and 6.6% reported nausea while eating. When asked to assess to what extent this was a perceived problem, 16.4% rated taste, 13.1% rated nausea, and 16.4% rated appetite as a “moderate” or “big” problem. Men with poor or very poor taste (1 or 2 on a 5 point Likert scale) had a significant association with poor appetite (OR = 7.9, P = 0.0002). There was no direct relationship observed between taste and weight loss. The population with poor appetite was more likely (OR = 21.25, P < 0.0001) to have had ≥ 5% weight loss as compared to those without a poor appetite. Those reporting at least some nausea were also (OR = 8.645, P = 0.0007) more likely to have ≥ 5% weight loss. In the treatment subset, pts on docetaxel at time of survey were 15.17 fold more likely to have poor taste as compared to those on abiraterone (p = 0.0145). Conclusions: We observed that perceived problems with taste were associated with loss of appetite which in turn was associated with weight loss. Weight loss is a known adverse prognostic factor in pts with advanced PCa. Further studies are warranted on this important patient-centric assessment.

Circulating tumor (ct)-DNA alterations in metastatic castration-resistant prostate cancer (mCRPC): Association with outcomes and evolution with therapy

149

Background: Cell-free ctDNA may be prognostic and evolve following therapy. We report ctDNA profiling of patients (pts) with mCRPC and their association with clinical outcomes and evolution with therapy. Methods: Pts with mCRPC that underwent baseline ctDNA analysis for potentially actionable alterations using Guardant360 before new systemic therapy were identified. Data were requested for clinical factors, current and prior therapy, TTF (time to failure) and survival. A 70-gene cfDNA next generation sequencing panel from a CLIA-licensed, CAP-accredited laboratory (Guardant Health, Inc.) offers complete exon sequencing for 29 genes, critical exons in 39 genes and amplifications (16 genes), fusions (6 genes) and indels (3 genes) harvested from 10 mL of peripheral blood. Alterations were reported and association of alterations with outcomes and prior therapy was examined. Results: Of 514 with confirmed mCRPC, 482 (94%) had ≥ 1 ctDNA alteration. The median age was 70 years (range 39-91). The most common recurrent somatic mutations were in TP53 (36% of patients), AR (22%), APC (10%), NF1 (9%), EGFR, CTNNB1 and ARID1A (6% each) and BRCA1, BRCA2 and PIK3CA (5% each) The most common genes with increased copy numbers were AR (30%), MYC (20%) and BRAF (18%). Clinical outcomes were available for 163 pts, of whom 46 (28.8%) were untreated for mCRPC. A higher number of ctDNA alterations was associated with shorter TTF (HR: 1.05, p = 0.026). AR alterations had a trend for shorter TTF (HR: 1.42, p = 0.053) and survival (HR: 2.51, p = 0.09). Pts who received prior therapy had new alterations in AR (56% vs. 37%, p = 0.028) compared to untreated pts. Serial ctDNA profiling of 64 pts revealed the evolution of alterations in AR, BRCA1 and BRCA2 following therapy. Conclusions: ctDNA was frequently detected in patients with mCRPC, and alterations appear similar to tumor tissue alterations. A higher number of overall gene alterations and AR alterations appeared associated with poor clinical outcomes and new AR and BRCA alterations appeared following therapy. These data suggest that developing salvage agents targeting AR alterations and PARP inhibitors hold promise.

Liver metastases in mCRPC patients post-therapy with abiraterone (Abi) and/or abiraterone/enzalutamide (Enza)

250

Background: Liver metastases (mets) are a particularly poor prognostic group among mCRPC patients. The objective of this study is to characterize mCRPC patients who have had treatment with Abi or Enza to identify risk factors that may be associated with subsequent development of liver mets. Methods: A sample of 67 patients (n = 17 liver mets and 50 non-liver met patients matched by treatment history) seen at Tulane Cancer Center were selected for analysis. All patients had prior Abi and or Abi/Enza. Race, age at PCa diagnosis and Gleason Score at PCa diagnosis were assessed. For patients with liver mets, total liver metastatic volume was measured using CT scans and correlated against PSA, LDH and AST values at the time of the scan. Wilcoxon rank sum tests were run analyzing PSA, LDH and AST at the start of Abi treatment, end of Abi treatment as well the duration of Abi treatment, and the nadir PSA for these patients. Results: Patients were predominantly Caucasian, had a median Gleason Score of 8 at diagnosis and were at a median age of 57 for those with liver mets and 62 for non-liver met at PCa diagnosis. Pearson correlation analysis of the total liver lesion volume and lab values revealed a significant correlation for LDH (R = 0.491, < 0.01) and AST (R = 0.368, p < 0.05), but not for PSA. Further evaluation of PSA and AST values at the start and end of Abi treatment as well as at nadir PSA revealed no statistically significant differences between liver met patients and non-liver met patients. However, there was a significant difference (p = 0.015) between LDH levels at the end of Abi treatment with a median of 347 U/L for liver met and 238 U/L for non-liver met patients. Conclusions: LDH and AST levels correlate with extent of liver metastases. Additionally, elevated LDH at the end of Abi treatment is indicative of an increased risk for developing liver metastases. Larger sample sizes and molecular characterization of these tumors are required to gain more insights into this important patient population.

Inherited pathologic mutations and family history in patients with prostate cancer

185

Background: In prostate cancer (PCa), germline pathogenic variants have previously been underestimated. PCa patients (pts) with DNA repair defects have a higher percentage of non-PCa family history (FH) with the most common cancers being derived from the breast, GI tract, ovary, pancreas, lymphoma/leukemia. The goal of this study was to evaluate and characterize pathogenic variants detected in PCa patients undergoing both enhanced FH screening and genetic testing. Methods: In this single-institution study, 535 PCa pts from Tulane Cancer Center over the last year underwent enhanced FH screening, and FH of PCa and other cancers were collected. 124 PCa pts including those with both localized and metastatic disease were identified to have a FH that met NCCN guidelines for genetic testing. Genetic testing was done using a commercially available panel (Invitae, San Francisco, CA) of 25-79 cancer-related genes for mutations and selected exonic deletions/duplications. Results: Of the 124 tested pts, 21 pts (16.9%) had ≥ 1 germline pathogenic variant (PV) and 47 pts (37.9%) had ≥ 1 germline variant of unknown significance (VUS). PVs included: BRCA2 (n = 4), BRCA1 (n = 3), CHEK2 (n = 3), MUTYH (n = 3), ATM (n = 2), TP53 (n = 2), MITF (n = 1), NBN (n = 1), PMS2 (n = 1), and (RAD51D (n = 1). Of the 124 tested pts, 68 pts (54.8%) had PCa FH, 68 (54.8%) had breast cancer FH, 22 (17.7%) had pancreatic cancer FH, 16 (12.9%) had ovarian cancer FH, and 37 (29.8%) had both breast and PCa FH. Between the pt groups (those with PVs, VUSs and negative results), there were no differences in FH rates of PCa, breast, pancreatic, or ovarian cancer. There was no significant difference in the age at diagnosis (dx) between the groups or between pts with PCa FH and those without. The median ages at dx were 65 for PV pts, 60 for VUS pts, and 59 for negative result pts. There were no statistically significant differences in initial Gleason score or metastatic disease status in these three groups (p = 0.35 and p = 0.66). Conclusions: In this dataset, FH cannot discriminate between those with and without inherited PV using a broad panel of genes that include those that alter DNA repair. The implications of these findings are broad. [Table: see text]

Association of cfDNA androgen receptor amplifications with BRAF alterations in mCRPC

234

Background: Cell free DNA (cfDNA) present in plasma of cancer pts can reflect tumoral alterations. Genomic alterations in cfDNA alter prognosis and abiraterone/enzalutamide resistance in mCRPC. The goal of this evaluation was to characterize AR amplifications (Amps) and various somatic point mutations (Muts) detected in mCRPC cfDNA and to relate those changes to other common alterations in the cfDNA landscape. Methods: A heterogenous group of 46 mCRPC patients (pts) with evidence of clinical progression from Tulane Cancer Center underwent cfDNA analysis using Guardant360 test (Guardant Health, Redwood City, CA). This evaluation included full exonic coverage of 70 genes and amplifications in 18 genes. Mutations reported herein include both known pathogenic mutations as well as mutations uncharacterized for functional importance. Results: 69.5% (n = 32) of the mCRPC pts evaluated had an AR alteration. Of the pts with AR alterations, 46.8% (n = 16) had AR Amps, 43.7% (n = 14) had AR Muts, and only 6.25% (n = 2) had both. In this cohort, AR alterations were the most commonly observed aberration. In addition to amplifications, 12 different AR Muts were detected. AR Muts included: T878A (n = 9), H875Y (n = 5), W742C (n = 4), AR L702H (n = 3), and others. To better understand the relationship between AR alteration and other commonly detected cfDNA aberrations, association between BRAF (35.5%), TP53 (46.7%), and MYC (22.2%) alterations and AR were assessed. Among these genes, TP53 alterations were all Muts and MYC alterations were all Amps. BRAF alterations were predominantly Amps (N = 15) though Muts were also detected (N = 6). Neither TP53 Muts or MYC Amps were significantly associated with AR alterations. On the other hand, BRAF alterations were significantly associated with AR Amps (p = 0.041); 60% (9/15) pts with AR Amps also had BRAF alteration (Odds ratio = 7.71, 95% CI 1.284- 46.366). Conclusions: AR alterations in cfDNA impact both disease progression and response to therapy. Co-segregation of AR and BRAF alterations may have significant prognostic and therapeutic implications. Further research and larger sample size is needed to further elucidate associations between the common somatic alterations detected in mCRPC.

Evidence of linkage in MSH6-associated region exclusive to high-risk African-American families with prostate cancer

180

Background: The significance of germline variants and their implications for prostate cancer (PCa) patients has gained prominence. Mismatch repair (MMR) genes such as MSH6 and MSH2, along with DNA repair genes, may be more important in PCa than previously appreciated. In the present study, we compared linkage results between African American (AA) and Caucasian (CA) PCa families with multiple affected family members. Methods: Study subjects were from 15 large, high-risk, clinically homogenous AA families and 4 CA families from Southern Louisiana. All families had at least ≥ 3 members with family member diagnosed with PCa. Genotyping for linkage analyses was done using Illumina Infinium II SNP HumanLinkage-12 panel. 6,068 SNPs were released for linkage analyses. Parametric linkage analyses were performed using Merlin software, version 1.1.2. An HLOD score > 1.86 was considered suggestive of linkage. Results: A total of 129 individuals from 15 AA families were genotyped including 45 affected men, 44 unaffected men, and 40 women. The average age at diagnosis was 61; 8 of 15 families had more than 4 affected individuals. 50 CA individuals from similar families were genotyped including 12 affected men, 26 presently unaffected men, and 12 women. For CA families, the average age of onset was 66, with at least 5 affected individuals in each family. In AAs, we identified a peak of suggestive linkage at chromosome 2p16 (HLOD = 1.97). Similarly, in CA families, the strongest linkage signal was observed on chromosome 2q14.1 with an HLOD score of 1.94. At the2 q14 linkage region, there was no linkage in AA PCa families (HLOD = 0.0004). Similarly, on 2p16, there was no linkage in the CA cohort (HLOD = 0). Conclusions: The MSH6 gene is located in 2p16 region. MMR gene mutations have been shown to have evidence of microsatellite instability in PCa as well as hereditary nonpolyposis colorectal cancer. MSH6 gene may represent a genetic variant contributing to risk of PCa in high risk AA families. This potentially has therapeutic implications for use of PD1 inhibitors in this population.

Baseline differences in characteristics of a racially diverse group of men electing active surveillance

103

Background: To date, large populations of men from European ancestry have been prospectively evaluated on Active Surveillance (AS), a strategy reserved for low risk prostate cancer (PCa). African Americans (AA) deemed to be candidates for AS have yet to be fully characterized. We sought to determine the similarities and differences of our AS cohort stratified by race. Methods: We identified 308 men from our multi-institutional, prospective AS database were analyzed. Inclusion criteria was PSA < 20ng/mL, Gleason score ≤ 7, and clinical stage ≤ T2a. Men who sought treatment for their PCa or refused subsequent imaging and biopsy were excluded. Univariate analysis was done to analyze racial differences in demographic, clinical and pathologic variables. Results: We identified 308 men, 131 (43%) AA and 177 nonAA (57%). The groups were not significantly different with respect to age; 65 years, BMI 28.4, family history of PCa (22%), prior negative biopsy (21%) and clinical staging (87% T1c). Median follow-up is 25 months (IQR 12-44). Significant differences between the AA and nonAA cohorts did exist at baseline with respect to overall health, suggesting AA having worse overall health. More AA had diabetes (29 vs 14%; p = .03), were smokers (55 vs 29%; p < .01), cardiovascular disease (21 vs 9%) and erectile dysfunction (43 vs 18%; p < .01). Social characteristics also differed within the groups, with AA less likely to be married (47 vs 51%; p = .01). Despite a lack of difference with respect to biopsy Gleason score, AA had higher PSA (5.7 vs 5.0 ng/mL; p = 0.02), lower testosterone levels (250 vs 334 ng/dL; p = 0.05), greater PSA density (0.15 vs 0.12; p < 0.01), and greater linear length of cancer per biopsy core (16 vs 13mm; p < 0.01) at time of diagnosis and initiation of AS. Conclusions: Within our AS cohort, AA have worse overall health and more aggressive PCa features despite meeting inclusion criteria and selecting AS. Further prospective study is needed to determine how these competing factors may impact long term outcomes.

Early assessment of PSA response in patients with mCRPC treated with enzalutamide and abiraterone

e574

Background: Abiraterone (Abi) and enzaleutamide (Enza) are first-line agents for the treatment of metastatic castrate-resistant prostate cancer (mCRPC). Primary resistance is well-documented, but little data exists for rapid treatment responders. This study intended to further characterize patients with early prostate-specific antigen (PSA) decline. Methods: A single-institution retrospective review was performed on 123 mCRPC patients treated with Abi and/or Enza. PSA was recorded every 4 weeks for the duration of treatment. The primary endpoint was to describe PSA response, including sensitivities and specificities, as a predictor of later treatment response (defined as ≥50% decrease in PSA from baseline). Additional clinical covariates were also evaluated as treatment-response predictors. Results: A PSA response to Abi was achieved in 52/123 (42%) of patients. Median time to PSA nadir was 37 days. 30/52 (58%) patients responded to the drug within 4 weeks. Median length of time on drug was 110 days. A PSA response to Enza was achieved in 21/123 (17%) of patients. Median time to PSA nadir was 140 days. 18/21 (86%) of patients responded to the drug within 4 weeks. Median length of time on drug was 161 days. Conclusions: Percentage of PSA decline and time to drug response for Enza and Abi are important variables that can serve as reliable way for clinicians to predict long-term PSA response. It is vital to make appropriate treatment modifications for patients that do not display early PSA response. [Table: see text]

Treatment sequencing of abiraterone and enzalutamide in patients with mCRPC

233

Background: Abiraterone (Abi) and Enzalutamide (Enza) are among the treatment modalities available for treating metastatic castrate-resistant prostate cancer (mCRPC). This study aimed to analyze the efficacy of Abi and Enza as direct sequential treatments for patients with mCRPC. Methods: A single institution retrospective review was performed on 66 patients, in which 52 (79%) of the patients received Enza following Abi. The primary outcome measure was PSA response (50% PSA decline). Patients treated with taxanes between Abi and Enza were excluded from these analyses. Results: In patients treated first with Abi and second with Enza (n = 52), 35/52 (67%) responded initially to Abi. Following PSA progression or lack of initial response, all 52 patients were then treated with Enza, and 15/52 (29%) responded. Of the 17 patients that did not initially respond to Abi, 9 (53%) patients had a PSA response to Enza, in which 5/9 had a PSA decline ≥ 50%. 14 patients had a PSA decline ≥ 50% on initial Abi only (no PSA declines at all were noted post-Abi) and 3/14 responded to Enza. The median duration on the 1st drug was 294 days; median duration on the 2nd drug was 89 days. Conclusions: Additional investigation is needed for clinicians to understand better the cross resistance of Abi and Enza in mCRPC patients. [Table: see text]

Family history, race, and prostate cancer

225

Background: African American (AA) race and family history (FH) of prostate cancer (PCa) increase the incidence and mortality of PCa. The goal of this study was to assess and compare FH in AA and Caucasian (C) men. Methods: During June 2015 through September 2016, 338 men with prostate cancer had FH collected at Tulane Cancer Center (C = 266 and AA = 72). A FH was defined as ≥ 1 1st degree relative with PCa and/or ≥ 2 affected 2nd/3rddegree relatives. Documented clinical factors were age at diagnosis (dx), Gleason score, incidence of radical prostatectomy (RP), and presence of metastases (at any time). Chi-square and Mann-Whitney U tests were performed to identify potential clinical correlates with regard to FH and race. Results: For demographics see table below. On average, men with a FH of PCa (n = 110) had a median age at dx of 59.6 as compared to those without a FH of PCa (n = 151) (median age at dx = 63.0). Overall FH patients (pts) were younger at dx (p = 0.00046). FH had a particularly impactful influence upon the age at dx for C men (p = 0.00086, 58 [n = 88] vs. 62.5 [n = 112]); statistics were limited for AA men. Gleason scores were not different between pts with or without a FH, and there was no relationship between Gleason score and race. Metastatic disease (mets) was detected in 23.97% of men (n = 93). C men with a FH of PCa (n = 40) were 1.55 times more likely to develop mets (p = 0.0352). AA data were limited so no comment can be made. No relationship was detected between the pts having undergone a RP and race, but pts with a FH of PCa (n = 61) were 1.39 times more likely to have undergone surgery (p = 0.016). Data by racial subsets were too limited to be conclusive. Conclusions: The study highlighted the significant impact that FH of PCa has upon age at dx and presence of mets. More AA data are needed to be conclusive. [Table: see text]

AR amplification eradication with high-dose testosterone (T) in patients with heavily pretreated mCRPC

251

Background: Patients (Pts) with mCRPC resistant to novel hormones (abi/enza) and taxanes pose a challenge for clinicians. Typically, once these agents are exhausted, clinical trials represent the best therapeutic option; however, many pts are not appropriate for clinical trials due to marrow suppression and/or extensive pre-treatments. Herein we present limited experience with three pts treated with high dose T when therapeutic clinical trial options were not available. Methods: Data was retrospectively collected at Tulane Cancer Center for pt treatment history, laboratory parameters, and circulating free-DNA genomic testing. High dose testosterone was used at a dose of 87.5-100 mg given daily as a 1% testosterone gel applied to the skin. Results: All the mCRPC patients were pre-treated with abi, enza, taxanes, & radium-223. All pts had RBC transfusions due to marrow suppression. All patients were previously treated on clinical trials. After starting high dose T, pt 1 demonstrated a clinical improvement in energy and appetite with a PSA decline from 530 to 45.8 ng/ml (-91.4%) over 30 days. At baseline, cfDNA analyses measured 15.9X AR amplification and 3.7X MYC amplification. The cfDNA also contained 9.8% of P53R273H mutation. Post high-dose T (serum T from castrate to 1462 ng/dL), both of the cfDNA measured amplifications returned to normal and P53 mutation declined to 0.5%. The PSA nadir occurred 30 days after T start; T was stopped 96 days after starting because of PSA rise to 280 ng/ml. The pt then restarted abi, despite prior resistance, and PSA declined from 280 to 65 ng/ml (-76.6%). The 2 other patients had PSA increases and clinical deterioration and high dose T was stopped after 2-3 weeks. Conclusions: Response to high dose T has been reported in occasional case reports going back over 60 years ago (see Brendler H et al. Arch Surg 1950;61:433–40). The frequency of favorable responses is unknown. In one case, a reversal of AR and MYC amplification was observed. The responding patient then was re-sensitized to abi, a drug to which he was previously resistant. Further research, such as the TRANSFORMER trial, is needed to understand the molecular changes and treatment options for this population.

Characterization of cancer family history among patients with PCa cancer

272

Background: Family history (FH) is a well-documented risk factor for prostate cancer (PCa). Certain cancers (Ca) are also shown to co-segregate in families. This study evaluated Ca FH in PCa patients (pts) and the impact of FH on clinical covariates. Methods: FHs were collected from 535 PCa pts at Tulane Hospital between 2015 and 2016. Incidence rates of familial Cas were analyzed. Age at diagnosis (dx), Gleason score, and the presence of metastases at any time were documented. Chi-square and the Mann-Whitney U tests were performed to identify correlations between clinical parameters and FH. Results: 435 pts (81.3%) had a Ca FH. 281 pts (52.5%) had ≥2 relatives with Ca. Rates of breast, lung, colorectal, pancreatic Ca, and leukemia FH did not vary between pts diagnosed at ≤55 and those diagnosed over 55. Pts with PCa FH were more likely than pts with no PCa FH to have an age of dx ≤55 (p= 0.0169). Median age at dx was 59 for pts with PCa FH and 64 for pts with no PCa FH. PCa FH did not affect Gleason score or the presence of metastases. Conclusions: PCa, breast, lung, and colorectal were the most common familial Cas reported. Pts with PCa FH were younger at dx than those without PCa FH. Further studies are needed to understand the co-segregation of PCa with other Cas and genetic studies are needed to clarify the mechanisms of these trends. [Table: see text]

Utility of PCA3 and TMPRSS2: ERG urinary biomarkers to predict pathologic outcomes in African American men undergoing radical prostatectomy

e547

Background: Tremendous disparity exists between preoperative characteristics and pathologic outcomes in men electing radical prostatectomy (RP) for localized prostate cancer (PCa). We sought to determine the performance characteristics of urinary PCA3 andTMPRSS2:ERG (T2:ERG) to predict pathologic outcomes in a racially diverse group of men undergoing RP. Methods: Following IRB approval, post digital rectal exam (DRE) urine was prospectively collected in consecutive patients with known PCa prior to RP. PCA3 and T2:ERG RNA copies were quantified and normalized to PSA mRNA copies using the Progensa assay (Hologic, San Diego, CA). Nonparametric Mann-Whitney U tests were performed to determine the ability of PCA3 and T2:ERG to predict higher risk PCa and notable disease features. Results: The cohort consisted of 214 men with PCa who underwent RP, and 89 men (42%) were African American (AA). The men in the cohort generally had higher risk disease, with 75% having AUA risk stratification of intermediate/high-risk PCa. PCA3 discriminated between biopsy low- and intermediate/high-grade Gleason Score (p = .005) and pathologic low- and intermediate/high-grade Gleason Score (p = 0.001). For men with low-risk PCa, PCA3 also predicted Gleason Score upgrading from biopsy to prostatectomy specimen (p = 0.003). PCA3 could not predict the presence of perineural invasion, lymph node positivity, seminal vesical invasion, positive surgical margins or extraprostatic extension. When stratified by race, within the AA cohort, T2:ERG did predict upgrading from Gleason 6 disease at the time of biopsy to higher grade pathology at RP (p = 0.016). However, T2:ERG was not predictive for the overall cohort, nor was it predictive for any of the disease features found to be significant with PCA3. Conclusions: In a racially-diverse group of men undergoing RP, PCA3 and T2:ERG urinary assays have limited ability to characterize aggressive pathologic features at the time of RP regardless of race.

Outcomes of men who underwent treatment for prostate cancer from a prospective follow up of a racially diverse, multi-institutional active surveillance cohort

e536

Background: Active surveillance (AS) is an increasingly accepted alternative to treatment for low-grade prostate cancer (PCa). However, it remains unclear what factors may predict which patients will upgrade to a higher grade cancer. We sought to analyze the characteristics at time of diagnosis and outcomes of those men in our racially diverse AS cohort who underwent treatment for PCa. Methods: Men from our AS database were analyzed. Inclusion criteria was PSA < 20 ng/mL, Gleason Score ≤ 7, and clinical stage ≤ T2a. Men who elected active treatment for their PCa at diagnosis or refused subsequent imaging and biopsy were excluded from this cohort. Univariate analysis was done to compare the clinical variables of the treatment group with the entire cohort. Results: We identified 56 men who were treated for PCa from the 308 men currently enrolled in our AS cohort. All 56 men in the treatment group had low risk PCa at diagnosis and initiation of AS. At diagnosis, the treatment group was not significantly different in comparison with our entire cohort with respect to age, BMI, family history of PCa, PSA at diagnosis, prior negative biopsy, TRUS volume, PSAD, smoking status and clinical staging. However the eventual treatment group did differ at diagnosis with respect to greater linear length of cancer per core (p < 0.01), greater % involvement of disease (p = 0.03), and greater number of total cores at time of diagnosis (p = 0.04). The men in this group underwent treatment for PCa for the following reasons: 36 for Gleason Score upgrading, 5 due to increased volume of disease, 6 due to rising PSA, 1 due to MRI findings, 1 due to rising PSA on Avodart and 7 elected treatment despite no significant changes in disease. 31 of the men had RARPs, 17 XRT, 4 had XRT + ADT, 3 had Brachytherapy, and 1 with XRT + salvage RP. Conclusions: Within our prospectively enrolled racially diverse AS cohort, the patients who underwent treatment for PCa had clinical factors that differed in comparison to the whole cohort. Further prospective study is needed to determine how these factors may ultimately impact long term outcomes.

Evaluating abiraterone responses in African Americans with metastatic CRPC

244

Background: A disparity between African American (AA) and other racial groups is documented in prostate cancer incidence and mortality. For metastatic CRPC, abiraterone (Abi) showed improvement in overall survival and gained FDA approval. However, Phase III trials enrolled mostly Caucasian (CA) patients. Documentation of Abi response rates in AA men is scant. Further characterization of Abi responses in AA men was the objective of this study. Methods: Age at diagnosis, prior enzalutamide (Enza) and/or docetaxel (Doc), and duration of Abi treatment were assessed. Baseline values at Abi initiation for alkaline phosphatase (ALP), hemoglobin (Hgb), and lactate dehydrogenase (LDH) were recorded. PSA values at baseline and throughout treatment were also logged. The velocity of PSA decline was determined by the PSA half-life (PSAHL) based on time to nadir. PCWG2 criteria were used to define PSA response and progression. Results: This was a single institution, retrospective cohort of 103 patients with mCRPC treated with Abi (n = 24 AA; n = 79 CA). Median age at diagnosis was 61.8 years and 62.4 years for AA and CA respectively. Prior Enza/Doc was 4.2%/33.3% for AA and 6.3%/29.1% for CA. Median duration of Abi therapy in AA was 207 days and 253 days for CA; neither median age or duration were statistically distinct. Median AA baseline ALP, Hgb, LDH, and PSA was 136 (range (r) = 59-653), 11.8 (r = 8.9-15.4), 256 (r = 157-401), and 59.9 (r = 4.8-1658) respectively. Median CA baseline ALP, Hgb, LDH, and PSA were 88 (r = 51-1600), 12.4 (r = 8.4-15.0), 204 (r = 100-528), and 40.6 (r = 2.5-2890) respectively. The difference in baseline lab values between AA and CA were insignificant. No statistical difference was seen in median PSAHL (AA = 55 days; CA = 64 days), or PSA decline of > 30% (AA = 50%; CA = 52%), > 50% (AA = 46%; CA = 39%), or > 90% (AA = 21%; CA = 14%). Finally, neither the median time to nadir (AA = 119 days; CA = 137 days) or progression (AA = 157 days; CA = 131 days) were significantly different. Conclusions: Comparison between AA men and CA men in mCRPC patients being treated with Abi showed no statistical difference in response rates, duration of response, or time to progression. Prospective, multi-institutional studies are needed to further assess these findings.