Prospective Genomic Profiling of Prostate Cancer Across Disease States Reveals Germline and Somatic Alterations That May Affect Clinical Decision Making

PURPOSE

A long natural history and a predominant osseous pattern of metastatic spread are impediments to the adoption of precision medicine in patients with prostate cancer. To establish the feasibility of clinical genomic profiling in the disease, we performed targeted deep sequencing of tumor and normal DNA from patients with locoregional, metastatic non-castrate, and metastatic castration-resistant prostate cancer (CRPC).

METHODS

Patients consented to genomic analysis of their tumor and germline DNA. A hybridization capture-based clinical assay was employed to identify single nucleotide variations, small insertions and deletions, copy number alterations and structural rearrangements in over 300 cancer-related genes in tumors and matched normal blood.

RESULTS

We successfully sequenced 504 tumors from 451 patients with prostate cancer. Potentially actionable alterations were identified in DNA damage repair (DDR), PI3K, and MAP kinase pathways. 27% of patients harbored a germline or a somatic alteration in a DDR gene that may predict for response to PARP inhibition. Profiling of matched tumors from individual patients revealed that somatic TP53 and BRCA2 alterations arose early in tumors from patients who eventually developed metastatic disease. In contrast, comparative analysis across disease states revealed that APC alterations were enriched in metastatic tumors, while ATM alterations were specifically enriched in CRPC.

CONCLUSION

Through genomic profiling of prostate tumors representing the disease clinical spectrum, we identified a high frequency of potentially actionable alterations and possible drivers of disease initiation, metastasis and castration-resistance. Our findings support the routine use of tumor and germline DNA profiling for patients with advanced prostate cancer, for the purpose of guiding enrollment in targeted clinical trials and counseling families at increased risk of malignancy.

Overall survival results of a randomized trial assessing patient-reported outcomes for symptom monitoring during routine cancer treatment

LBA2

Background: We previously reported significant benefits in quality of life, patient satisfaction, and emergency room utilization outcomes from a large single-center randomized controlled trial comparing web-based symptom monitoring with patient-reported outcomes (PROs) vs. usual care in patients receiving chemotherapy for metastatic solid tumors (Clinicaltrials.gov: NCT00578006). We now present overall survival results from this trial. Methods: Patients receiving routine outpatient chemotherapy for metastatic solid tumors at Memorial Sloan Kettering Cancer Center were randomly assigned to self-report 12 common symptoms via tablet computers (“PRO intervention”), or to usual care. Treating physicians received symptom printouts at visits and nurses received email alerts when participants reported severe or worsening symptoms. Overall survival was tabulated based on medical records and Social Security Death Index data, estimated using the Kaplan-Meier method, and compared between arms using a log-rank test and Cox proportional hazards regression adjusting for age, sex, race, education level, and cancer type. Results: Between September 2007 and January 2011, 766 patients were randomized, with median age 61 (range 26-91), 86% white, 58% female, and 22% with less than high school education. Cancer types included genitourinary (32% of patients), gynecologic (23%), breast (19%), and lung cancer (26%). Survival results were assessed in June 2016 after a median follow up of 7 years and 517/766 (67%) of participants had died. Median overall survival in the PRO intervention arm was 5 months longer than the control arm (31.2 vs. 26.0 months, p = 0.03). In the multivariable model, results remained statistically significant with a hazard ratio of 0.832 (p = 0.04; 95% CI; 0.696, 0.995). Conclusions: Systematic symptom monitoring during outpatient chemotherapy using web-based patient-reported outcomes confers overall survival benefits. These single-center results are being further evaluated in a national multicenter implementation trial. Clinical trial information: NCT00578006.

Performance of a high-intensity 508-gene circulating-tumor DNA (ctDNA) assay in patients with metastatic breast, lung, and prostate cancer

LBA11516

Background: ctDNA assays can noninvasively assess tumor burden and biology by identifying tumor-derived somatic alterations. For broad applicability, including early cancer detection, an unprecedented high-intensity approach (ultra-deep sequencing of plasma cell-free DNA (cfDNA) with broad genomic coverage) is needed to address intra-patient and population-level heterogeneity. We present initial results with this approach in patients (pts) with metastatic breast (BC), non-small cell lung (NSCLC), and castration-resistant prostate cancer (CRPC). Methods: Blood and tissue were prospectively collected w/in 6 wks with no intervening therapy change from pts with de novo or progressive cancer. cfDNA and white blood cell (WBC) genomic DNA from each pt were sequenced with a 508-gene panel (2 Mb; >60,000X raw depth). cfDNA variant calling used molecular barcoding for error correction and filtering for WBC variants. Tissue was sequenced using the MSK-IMPACT assay (410 genes, 1.4 Mb, >500X depth) blinded to plasma/WBC sequencing. Variants were classified as clonal or subclonal based on tumor sequencing in BC and NSCLC. Results: Of 161 eligible pts, 124 (39 BC, 41 NSCLC, and 44 CRPC) were evaluable for concordance. In tissue, 864 variants were detected across the 3 tumor types, with 627 (73%) also detected in plasma: single nucleotide variants/indels - 75%, fusions - 67%, and copy number alterations - 58%. In 90% of pts, at least 1 of the variants detected in tumor tissue was also detected in plasma: BC - 97%, NSCLC - 85%, CRPC - 84%. Most actionable mutations detected in tissue were also detected in plasma (54/71, 76%; SNVs only: 28/31, 90%). A subset of driver mutations (eg. in ESR1, PIK3CA, ERBB2, EGFR) were observed in plasma but not tissue. Clonal variants in tissue were more likely to be detected in plasma than subclonal variants (p<.001). Conclusions: This novel, high-intensity ctDNA assay enabled broad detection of genomic variants in plasma at high rates of concordance with corresponding tumor tissue, providing strong evidence for tumor-derivation of these signals. This study will inform development of a high-intensity sequencing approach for early cancer detection.

The immunomodulatory protein Dickkopf-1 (DKK1) defines a non-neuroendocrine subtype of metastatic castration-resistant prostate cancer (mCRPC) with low AR and low PSA expression

5054

Background: Advanced stagemCRPC can manifest AR-signaling independent growth typified by loss of AR and/or PSA expression in the absence of neuroendocrine (NE) features on biopsy. We sought to identify therapeutically relevant biomarkers of this highly resistant prostate cancer subtype. Methods: An unbiased differential gene expression analysis of non-neuroendocrine mCRPC biopsies was carried out comparing patients with ARlow to patients with ARhigh disease in a discovery cohort (SU2C/PCF, 18 pts: 8 ARlow, 10 ARhigh) and validation cohort (Fred Hutchinson, 76 pts: 12 ARlow, 64 ARhigh). The AR and NE status of the biopsies were defined by AR and PSA mRNA expression and gene signatures representative of AR activity and NE lineage. An RNA sequencing-based signature of immune cell subsets was calculated using the Cibersort algorithm. Results: Differential gene expression analysis identified the secreted Wnt antagonist, DKK1, as significantly upregulated in ARlow cases compared to ARhigh cases (11.2 RPKM vs. 0.28 RPKM, p < 0.03) in our discovery cohort and confirmed in our validation cohort (9.2 FPKM vs. 0.99 FPKM, p < 0.001). DKK1 protein was also found to be increased in non-neuroendocrine ARlow relative to ARhigh prostate cancer in vitro cell and organoid models (858 pg/mg total protein vs. 2 pg/mg total protein, p < 0.05) and patient-derived xenografts (28.6 FPKM vs. 0.78 FPKM, p < 0.0001). Consistent with the role of DKK1 as a negative modulator of anti-tumor immunity, patient biopsies with the highest quartile of DKK1 expression showed an RNA signature consistent with lower levels of active NK cells (0.2% vs. 1.8%, p < 0.005), and lower levels of CD8+ T cells (3.7% vs. 9.7%, p< 0.005) compared to those with the lowest quartile of DKK1 expression. Conclusions: DKK1 represents a secreted biomarker that is disproportionately enriched in non-neuroendocrine mCRPCs that lack AR expression. Because DKK1 has been implicated as a suppressor of anti-tumor immunity and is a target of an existing neutralizing antibody, our results support the clinical evaluation of the role of DKK1 blockade in DKK1-positive AR-negative prostate cancer.

Performance of a high-intensity 508-gene circulating-tumor DNA (ctDNA) assay in patients with metastatic breast, lung, and prostate cancer

LBA11516

The full, final text of this abstract will be available at abstracts.asco.org at 7:30 AM (EDT) on Saturday, June 3, 2017, and in the Annual Meeting Proceedings online supplement to the June 20, 2017, issue of the Journal of Clinical Oncology. Onsite at the Meeting, this abstract will be printed in the Saturday edition of ASCO Daily News.

Trop-2 expression on treatment resistant cancer cells in castrate-resistant prostate cancer (CRPC) as a predictive biomarker for targeted therapy

5045

Background: Trophoblastic cell-surface antigen (Trop-2) is a transmembrane glycoprotein that is highly expressed in many solid tumors. Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate of an anti-Trop-2 humanized antibody with SN-38. Early clinical trials have shown high response rates in a broad range of diseases including triple negative breast and urothelial cancers. We evaluated Trop-2 expression in tumor biopsies and circulating tumor cells (CTCs) from men with mCRPC (metastatic castrate-resistant prostate cancer). Methods: Trop-2 expression was evaluated from mCRPC biopsies from patients (Pts) treated with abiraterone acetate (AA) on the PROMOTE clinical trial, CTCs from a separate cohort treated with either enzalutamide or AA. Trop-2 CTCs were compared with EpCAM captured CTCs using a microscale technology termed the VERSA (Vertical Exclusion-based Rare Sample Analysis) platform to compare protein and gene expression signatures of resistance to these agents. Results: RNA sequencing identified Trop-2 gene expression in > 70% of metastatic biopsies. The AR splice variant V7 was found in 48 biopsies that also expressed Trop-2. Trop-2 expression was not altered by treatment with AA at 12 weeks. The number of CTCs captured from 25 pts with Trop-2 or EpCAM were closely correlated (R2= 0.84). Gene expression analysis showed similar patterns of expression for the TROP-2 and EPCAM captured cells. AR splice variant expression (AR-V7, AR-V9) in Trop-2 and EpCAM CTCs was detected in 33% of patients. Expression of neuroendocrine markers was identified in 40% of Trop-2 CTCs. Conclusions: Trop-2 is frequently expressed in mCRPC and co-expressed in tumors that express AR splice variants. Trop-2 CTCs are detected in CRPC pts previously treated with AA or Enzalutamide that also express multiple AR splice variants and neuroendocrine markers. The results support Trop-2 expression as predictive biomarker of sensitivity to targeted therapies tumors resistant to AA or Enzalutamide. Men with mCRPC are being enrolled on a Phase I trial with IMMU-132, and multi-site Phase II clinical trial in men who have progressed on AA or Enzalutamide is being finalized.

Circulating tumor cells (CTCs) N-terminal androgen receptor expression to identify patients (pts) with castrate resistant prostate cancer (CRPC) who are more sensitive to chemotherapy

5034

Background: Loss of the retinoblastoma tumor suppressor (RB) function was identified as a major means to develop CRPC; the expression of the androgen receptor (AR) is under stringent RB control; and tumors devoid of RB function are hypersensitive to treatment with chemotherapy. Exploratory analysis evaluated baseline N-terminal AR expression in CTCs in men with chemotherapy-naïve CPRC and correlated to changes in PSA, leading us to inquire if this biomarker may identify pts sensitive to chemotherapy. Methods: In a multicenter phase II randomized trial of approved doses of abiraterone acetate/prednisone (AA-Arm 1) or combination AA and standard doses of cabazitaxel (AA/CBZ-Arm 2). Patients on AA received CBZ upon progression. Baseline CTCs were obtained on all pts and expression of N-terminal AR expression was performed by Epic Sciences. Positive AR N-terminal expression (AR+) was based on the presence of at least 1 CTC or CK- cell with AR N-terminal signal expression above the 3.0 positivity threshold. Serial PSAs were determined at baseline and every 3 weeks with routine labs and imaging every 12 weeks. Results: To date, 42 of 80 pts have been enrolled: 22 pts to AA, and 20 pts to AA/CBZ. Both regimens were well tolerated with 8/42 (19%) pts experiencing treatment-related grade 3 or 4 toxicities. Blood from 35 patients underwent CTC analysis. Seventy-seven percent of pts (27/35) had detectable CTCs; 11 of 35 pts (31%) had AR overexpression. Of the pts with AR+ CTCs, 1/5 pts treated with AA, and 5/6 pts treated with AA/CBZ had a PSA decline > 50% from baseline. Conclusions: Real-time CTC analysis of N-terminal AR expression was feasible and data suggests that this may identify a cohort of pts who may benefit from the combination of CBZ with AA. Further studies are ongoing to evaluate whether cellular heterogeneity and RB expression in CTCs play a role in identifying pts who would benefit from chemotherapy. The trial is coordinated by the Prostate Cancer Clinical Trials Consortium, LLC and funded by Sanofi US Services Inc. and Prostate Cancer Foundation. Clinical trial information: NCT02218606.

Circulating tumor cell (CTC) number as a response endpoint in metastatic castration resistant (mCRPC) compared with PSA across five randomized phase 3 trials

5007

Background: Radiographic progression and overall survival (OS) are the traditional clinical benefit measures for mCRPC trials. Reliable indicators of response that occur early are a critical unmet need in practice and clinical research. We explored a week 13 CTC and prostate-specific antigen (PSA) endpoint relative to baseline in 5 prospective randomized phase 3 registration trials that enrolled 5912 pts. OS was the primary endpoint. Methods: CTC number (CellSearch) and PSA values in patients who survived at least 13 weeks were evaluated as response endpoints in COU-AA-301, AFFIRM, ELM-PC-5, ELM-PC-4 and COMET-1. Pts with missing values at week 13 were considered non-responders. The endpoints considered are shown in Table 1. Results: The discriminatory strength of the response endpoints with respect to OS was estimated using the weighted c-index. To summarize discrimination results for each measure, the mean and the standard deviation based on the weighted c-indices from the 5 studies were computed. Conclusions: CTC0 and CTC conversion endpoints had the highest discriminatory power for OS relative to the % decline in CTC or PSA endpoints. The percent of pts eligible and evaluable for the CTC0 endpoint was significantly higher than the conversion endpoint, 75% vs. 51%, respectively. These two absolute measures of CTC can be considered meaningful response indicators in mCRPC clinical trials. [Table: see text]

[Table: see text]

Overall survival results of a randomized trial assessing patient-reported outcomes for symptom monitoring during routine cancer treatment

LBA2

The full, final text of this abstract will be available at abstracts.asco.org at 7:30 AM (EDT) on Sunday, June 4, 2017, and in the Annual Meeting Proceedings online supplement to the June 20, 2017, issue of the Journal of Clinical Oncology. Onsite at the Meeting, this abstract will be printed in the Sunday edition of ASCO Daily News.

Translating prostate cancer working group (PCWG) criteria into a quantitative progression biomarker in metastatic castration resistant prostate cancer (mCRPC)

5068

Background: mCRPC is a bone dominant lethal disease. A validated endpoint in mCRPC trials is bone scan progression, which is semi-quantitative and rely on the appearance of new lesions as proposed by the PCWG. The validated automated bone scan index (BSI) quantifies the bone tumor burden as the fraction of total skeletal weight. To build on the current definition of disease progression, we sought to compare the association of time to progression with overall survival (OS) using PCWG criteria and BSI increase. Methods: mCRPC patients (pts) enrolled on trials of agents targeting androgen-receptor (AR) were assessed. Pts were required to have a raw bone scan image for BSI analysis concurrent with disease assessments. The EXINI automated computing platform generated the BSI values. Thresholds for the absolute and relative increase in BSI from 1st follow-up (≤12 weeks) were explored for the time to BSI progression. The association with survival time was computed for each threshold defined time to BSI progression. Kendall’s Tau, derived from the Clayton copula, was used to associate time to BSI progression with survival time, where both endpoints may be censored. Results: A total of 257 pts were assessed, of whom 169 had raw bone scans images needed for the BSI analysis. 90 pts (53%) met progression by PCWG criteria, the association between the time to PCWG progression and OS was 0.52. The association between time to BSI progression and OS was comparable to the PCWG progression when the absolute increase in BSI was 0.6 or more (table below). Conclusions: Progression in bone can be expressed as a single quantitative metric that describes the increase in total disease burden while retaining the same association that PCWG has with OS. These data represent the first steps to a quantitative expression of bone disease progression as a clinical trials endpoint. [Table: see text]

Next-generation sequencing (NGS) of tissue and cell free DNA (cfDNA) to identify somatic and germline alterations in advanced prostate cancer

5010

Background: With the goal of accelerating enrollment onto appropriate clinical trials, we performed prospective genomic characterization of pts with advanced prostate cancer. Given the long natural history and osseous disease predominance, we also analyzed plasma cfDNA to assess the feasibility of identifying targetable alterations in pts for whom adequate tumor tissue was unavailable. Methods: 1038 tumors from 896 pts along with matched normal DNA were analyzed with a capture-based NGS assay (MSK-IMPACT) targeting 341–468 genes. In 5/2015, the protocol was amended to allow pts to opt-in for a formal germline analysis of 76 genes associated with heritable cancer risk. In select pts, plasma cfDNA was collected and analyzed using the same assay. Results: Between 2/2014 and 2/2017, 576 primary tumors and 462 metastases were sequenced. The most notable finding was the high frequency of known or likely pathogenic germline and somatic mutations in genes that regulate DNA damage response (DDR). In the subset with both tumor and germline analysis, 28.84% (169/586) had a DDR mutation identified compared to only 10.65% (33/310) of pts with somatic only analysis. In the subset with tumor and germline analysis, 9.39% (55/586) had somatic only DDR mutations and 16.38% (96/586) had germline only DDR mutations, including 8 pts with two germline mutations. 3.07% (18/586) had co-occurring somatic and germline DDR mutations, with only 0.68% (4/586) involving the same DDR gene (all BRCA2). Prostate cancer had the highest tissue failure rate among the overall MSK-IMPACT solid tumor cohort, and bone biopsy-derived tissue was successfully sequenced in only 42% of pts. Profiling of cfDNA did identify somatic DDR or AR mutations in 12.5% (4/32) of pts without adequate tumor for analysis. Conclusions: This prospective genomic profiling effort identified frequent somatic and germline DDR mutations that may guide PARPi or platinum therapy. Both somatic and germline analyses were required to identify all pts with likely pathogenic DDR alterations. NGS-based cfDNA analysis is feasible in advanced prostate cancer and may identify mutations missed by tumor only sequencing.

Clinical outcome of metastatic castration-resistant prostate cancer (mCRPC) patients (pts) with a post-treatment circulating tumor cell (CTC) of 0 vs CTC > 0: Post hoc analysis of COU-AA-301

5015

Background: Assessment of radiographic response by RECIST in the majority of mCRPC pts is limited by the lack of measurable disease. Changes in CTC counts (CTCs) enumerated using Veridex CellSearch from unfavorable at baseline (BL [≥ 5 cells/7.5 mL]) to favorable (≤ 4) are prognostic for survival, and the test is FDA cleared as an aid in the monitoring of metastatic PC. The CTC cutpoint of ≥ 5 excludes many pts from response assessment. Examining CTCs alone and in combination with other biomarkers as a potential surrogate for clinical benefit was a secondary objective of COU-AA-301, a phase 3 trial of abiraterone acetate + prednisone vs prednisone alone in mCRPC. Methods: Pts from both treatment (tmt) groups with BL CTC > 0 were combined to assess CTC = 0 as a response criterion. Association between CTC response, defined as BL CTC > 0 and post-BL CTC = 0, and clinical outcomes was assessed. CTCs were determined at BL and 4, 8, and 12 wks. Pts with BL CTC > 0 and missing post-tmt CTCs were considered nonresponders. Radiographic response was first assessed at Wk 12. Overall survival (OS) was estimated using the Kaplan-Meier method. Results: Among739 pts with BL CTC > 0, 141 had measurable disease. At Wk 12, 19% (141/739) of pts were CTC responders and 81% (598/739) were CTC nonresponders. Among CTC responders, 74% (104/141) had stable disease or better by RECIST; 26% (37/141) were either not evaluable or had disease progression by RECIST. Median OS was 23.8 and 10.0 mos for CTC responders (n = 141) and nonresponders (n = 598), respectively. Among pts with liver and/or lung metastases, 86% (24/28) of CTC responders at Wk 12 had stable disease or better by RECIST; 14% (4/28) had disease progression by RECIST. Median OS was 19.9 and 7.1 mos for CTC responders (n = 28) and nonresponders (n = 127), respectively. Similar results were observed in Wk 8 CTC responders. Conclusions: For mCRPC pts with BL CTC > 0, CTC response on tmt (CTC = 0) is associated with longer survival and could be considered a response criterion. Additional analysis is required to fully characterize the relationship between CTC = 0 and objective response by RECIST in pts with measurable disease. Clinical trial information: NCT00638690.

Baseline CTC subtype to predict outcomes on mCRPC patients (pts) receiving enzalutamide (E) compared to abiraterone (A)

5070

Background: Prior response to A or E does not predict sensitivity to E following A or A following E. The detection of AR-V7 predicts insensitivity to either drug, but identifies only a portion of non-responders. We previously identified 15 CTC subtypes based on unique phenotypic features in mCRPC pts, each with unique biology and different degree of likelihood of predicting resistance to either drug. Here we explored the relationship between individual subtypes and sensitivity to A vs. E, but not both. Methods: 107 pre-treatment blood samples from mCRPC pts starting A (n = 47) or E (n = 60) as a 1st or 2nd line of Tx were analyzed for CTCs utilizing the Epic Sciences platform. Samples were assayed for CTC subtypes based upon 15 pre-defined phenotypic CTC classifiers (Type A-O). Treatment outcomes were assessed by serial PSA changes and landmarked percent time of therapy progression on radiographs, and overall survival following either A or E. Cell type prevalence was also analyzed in relation to clinical outcomes, and subsets of the CTC subtypes subject to single cell NGS to ascertain genomic drivers common to each subtype. Results: CTCs were identified in 94% (101/107) of pt samples. One, cell Type K, found in 25% (27/107) of pts, was associated with a statistically significant inferior outcomes on E for all measures. Whereas similar outcomes were seen between K+ & K- pts treated with A. The distinct features of Cell Type K include a large nucleus, high nuclear entropy and high Nuclear/cytoplasmic AR terminal ratio; and a unique genomic profile enriched for cell cycle and DNA repair alterations relative to other CTC subtypes. Conclusions: The presence of specific CTC subtypes in pre-Rx phlebotomy samples associated with outcomes on A or E. A CTC subtype (Cell Type K) helped to identify pts with poor outcomes on E but not A vs. those without the cell type. Further biologic interrogation of K cells and ongoing clincial validation of the CTC subtype is planned. [Table: see text]

Changes in CTC burden and prevalence of specific CTC subtypes in mCRPC patients (pts) receiving alpharadin (Ra-223) as single agent or in combination with other therapuetics (Tx)

5076

Background: Ra-223 prolongs life in mCRPC pts with symptomatic osseous metastasis with inconsistent effects on PSA. Survival times are prolonged further when combined with Abi/Enza. Data from preclinical studies suggest that Ra-223 may sensitize tumors to DDR agents and/or biologic therapies. But predictive biomarkers of benefit to each or both combinationso are lacking. We studied CTC counts and the prevelance of specific CTC subtypes in patients before and following Ra-223 therapy, both as a single agent and in combination, to identify biomarkers of sensitivity and treatement efficacy, and effects of Ra-223 on tumor biology. Methods: Pre and ~4 week post RA-223 therapy blood samples were collected from 35 pts (2 samples each) given as a single agent (n = 20 pts) or in combination with other therapies (n = 15 pts, 9 w/ Enza, 5 w/ Abi, 1 w/ Taxane). Samples were processed and CTCs analyzed using the Epic Sciences platform. Total CTC count and the prevalence of specific CTC phenotypes present pre and post Rx were identified utilizing high content digital pathology and associated with therapy type and post-treatment change. Results: CTC declines were observed in 55% (11/20) and 60% (9/15) of pts treated with single agent and combination respectively. In Ra-223 alone pts, a novel CTC subtype (high N/C ratio, high nuclear area) was identified at baseline 11/20 samples (med = 33% of CTCs). Which was no longer detected in 10 (90%) of the pts treated. This contrasts with a second novel CTC subtype present at baseline in 4 pts (med CTC = 9%) that increased to 9 cases (med CTC = 18%) at follow-up. Conclusions: A subset of pts demonstrate post-therapy CTC declines following Ra-223 alone or in combination. A novel CTC subtype resolved by RA-223 in conjunction with total CTC kinetics may indicate pt benefit from Ra-223. A novel emergent CTC subtype has also been identified in pts already receiving Ra-223. Single CTC sequencing and protein analysys of these CTC subtypes are ongoing, and may help describe tumor evolution and sensitization to novel therapuetics.

Mutational landscape of metastatic cancer revealed from prospective clinical sequencing of 10,000 patients

Tumor molecular profiling is a fundamental component of precision oncology, enabling the identification of genomic alterations in genes and pathways that can be targeted therapeutically. The existence of recurrent targetable alterations across distinct histologically defined tumor types, coupled with an expanding portfolio of molecularly targeted therapies, demands flexible and comprehensive approaches to profile clinically relevant genes across the full spectrum of cancers. We established a large-scale, prospective clinical sequencing initiative using a comprehensive assay, MSK-IMPACT, through which we have compiled tumor and matched normal sequence data from a unique cohort of more than 10,000 patients with advanced cancer and available pathological and clinical annotations. Using these data, we identified clinically relevant somatic mutations, novel noncoding alterations, and mutational signatures that were shared by common and rare tumor types. Patients were enrolled on genomically matched clinical trials at a rate of 11%. To enable discovery of novel biomarkers and deeper investigation into rare alterations and tumor types, all results are publicly accessible.

Evaluation of Castration-Resistant Prostate Cancer with Androgen Receptor-Axis Imaging

Castration-resistant prostate cancer (CRPC) is the lethal form of prostate cancer, and more than 26,000 men will die from this disease in 2016. The pathophysiology of CRPC is clearly multifactorial, but most often, androgen receptor (AR) upregulation is associated with its earliest beginnings and the AR increase is part of the multimolecular complex including downstream effector proteins linked to AR (AR-axis) responsible for rapid proliferation and malignant features of the malignant cell. In both animal models and patients, glycolysis (Warburg effect) is also an early manifestation of CRPC transformation. At Memorial Sloan Kettering Cancer Center, we have focused our energies on imaging studies of the AR-axis in CRPC, using ¹⁸F-FDG, ¹⁸F-16β-fluoro-5α-dihydrotestosterone (¹⁸F-FDHT), and a variety of radiolabeled antibodies targeting downstream effectors, such as prostate-specific membrane antigen (PSMA). Small-molecular-weight PSMA-targeting agents are not part of this review. In this review, we will focus on molecular imaging of the AR-axis in metastatic CRPC (mCRPC) and discuss our personal experience with these tracers. Our goal is to put these radiopharmaceuticals in the context of mCRPC biology and diagnosis (e.g., ¹⁸F-FDHT).

Collaborating to Compete: Blood Profiling Atlas in Cancer (BloodPAC) Consortium

The cancer community understands the value of blood profiling measurements in assessing and monitoring cancer. We describe an effort among academic, government, biotechnology, diagnostic, and pharmaceutical companies called the Blood Profiling Atlas in Cancer (BloodPAC) Project. BloodPAC will aggregate, make freely available, and harmonize for further analyses, raw datasets, relevant associated clinical data (e.g., clinical diagnosis, treatment history, and outcomes), and sample preparation and handling protocols to accelerate the development of blood profiling assays.

A phase II study combining ipilimumab and degarelix with or without radical prostatectomy (RP) in men with newly diagnosed metastatic noncastration prostate cancer (mNCPC) or biochemically recurrent (BR) NCPC

203

Background: Androgen deprivation therapy (ADT) does not completely eliminate disease in mNCPC or BRPC. We explored a multimodality treatment (tx) approach combining ADT with ipilimumab (ipi) with the aim of achieving no evidence of disease or complete elimination of disease, given the potential for cure seen with immunotherapy. Methods: Cohort A (Coh A) enrolled men with ≤ 10 bone metastases treated with induction of degarelix (deg) and ipi prior to RP and subsequent ipi q3 weeks x 3 and 8 months (mos) total of deg. Cohort B (Coh B) opened later and enrolled men with BRNCPC after RP with a doubling time ≤ 12 mos, and received ipi q3 weeks x 4 and 8 mos of deg. The primary endpoint was an undetectable PSA (<0.05) at 12 and 20 mos with non-castrate testosterone. Results: 16 pts (7 Coh A; 9 Coh B) were treated. No Coh A pts experienced immune related toxicities (irAE) that delayed surgery. 4/7 (57%) Coh A pts came off study for irAE, 1 (14%) for insurance reasons, and 2 (29%) completed all protocol requirements. In Coh B 6/9 (67%) pts have completed tx and entered follow-up. Conclusions: A combined modality approach with ipi 10mg/kg, ADT, and RP in mNCPC was associated with limiting toxicities, however 3mg/kg was better tolerated and more feasible in a BRNCPC cohort. One pt in Coh A (14%) had an undetectable PSA with testosterone recovery while evaluation of efficacy for Coh B is ongoing. The role for RP and other immunotherapeutic approaches in NCPC remain viable interests to the field. Clinical trial information: NCT02020070. [Table: see text]

Glucocorticoid receptor (GR) expression in circulating tumor cells (CTCs) to prognosticate overall survival (OS) for metastatic castration-resistant prostate cancer (mCRPC) patients (pts) treated with androgen receptor signaling inhibitors (ARSi)

194

Background: Upregulation of GR protein expression in metastatic biopsies from pts with CRPC has previously been shown to correlate with resistance to enzalutamide and has been validated as a therapeutic target in pre-clinical studies. We sought to determine whether upregulated GR protein expression in CTCs from pts with progressing mCRPC predicted clinical outcomes following treatment with enzalutamide (E) or abiraterone (A). Methods: Pre-therapy blood samples from 54 pts with progressing mCRPC were subjected to CTC analysis using the Epic Sciences platform. Samples were examined to identify CK+ (CK+, CD45- cells, with intact nuclei, morph distinct) CTCs for GR protein expression. GR+ CTCs were defined as having expression greater than the 95th percentile of GR expression in the GR negative LNCAP cell line. Kaplan-Meier analysis was used to test the impact of GR+ CTCs on OS following treatment with A or E. A Cox proportional hazards model with CTC number and GR positivity was used in a multivariate analysis. Results: 37 out of 54 pts (69%) had detectable and viable CK+ CTCs. 28 out of 37 pts (76%) had CTCs with upregulated GR staining with a median of 6 GR+/CK+ cells/ml per patient (range 0.7 – 244 cells/ml). The OS of patients with GR+ CTCs treated with ARSi was significantly worse than that of patients without detectable GR+ CTCs (11.4 mo. vs NA, p < 0.01), an effect independent and additive to the presence of viable CTCs, a previously described prognostic biomarker (see Table). Conclusions: GR protein upregulation in CTCs can be detected in a significant percentage of pts with progressing mCRPC and the presence of GR+ CTCs predicts worse OS in response to ARSi. The data supports previously reported pre-clinical data proposing a pathogenic role for GR in mediating resistance to ARSi therapy. Detection of GR in patient CTCs may be a useful predictive biomarker to guide GR-directed therapies. [Table: see text]

Translating Prostate Cancer Working Group 2 (PCWG2) progression criteria into a quantitative response biomarker in metastatic castration-resistant prostate cancer (mCRPC)

170

Background: PCWG2 radiographic progression criteria, which are associated with survival, rely on lesion counting. There is a need for a fully quantitative assessment of tumor burden as a component of a true response biomarker for mCRPC. Here, we used the bone scan index (BSI) to fully quantitate the increase in skeletal disease burden at each radiographic milestone that constitutes the PCWG2 criteria. Methods: mCRPC patients (pts) from clinical trials using PCWG2 criteria to determine progression (PD) were assessed. Pts were required to have baseline (BL) and at least two follow-up (FU) bone scans. The EXINI automated platform was used to generate BSI at key PCWG2 landmarks: 2+2 criteria for early PD and post flare PD criteria with the appearance of 1 and ≥2 new lesions. Median (M) and Interquartile range (IQR) of the relative change in BSI were calculated to quantify the increase in total tumor burden. Results: A total of 257 pts were assessed, of whom 169 had two or more FU bone scans at 8 or 12 week intervals. Of the total 169 pts, 86 (51%, 95%CI 43-58) met PD by PCWG criteria. 35 (41%, 95%CI 31-51) of 86 pts met the early PD criteria, the remaining 51 (59%, 95%CI 49-69) met PD at subsequent time points after flare period. The ability of the automated platform to reproduce a BSI value, retrieved from the same scan, was highly consistent (100%). The relative BSI increase during the course of meeting PD by PCWG2 is shown in the Table. Conclusions: This is the first quantitative assessment of changes in total tumor burden in pts meeting PCWG2 criteria. Relative changes in BSI can be substantial in meeting the criteria. These data build on the PCWG2 criteria by quantitating the increase both of existing lesions and the contribution of new lesions. We are now assessing the associations with survival that these incremental increases represent. [Table: see text]

Evaluation of a multimodal strategy to accelerate drug evaluations in early-stage metastatic prostate cancer

187

Background: The paradigm of first testing systemic treatments in advanced disease followed by development in earlier disease states and finally large-scale trials evaluating whether the approach, in combination with local therapy, can prevent or delay the time-to-event measures of disease progression or death in patients with “high-risk” tumors is no longer practical now that 6 life-prolonging systemic therapies in metastatic castration-resistant prostate cancer are available. New strategies are needed to rapidly evaluate and prioritize regimens for large-scale phase 3 testing. Methods: We conducted a pilot study of twenty men with oligometastatic M1a (extrapelvic nodal disease) or M1b (bone disease) at diagnosis. All sites of disease were treated using a multimodal approach that included androgen deprivation (ADT), radical prostatectomy plus pelvic lymphadenectomy (retroperitoneal lymphadenectomy in the presence of clinically positive retroperitoneal nodes), and stereotactic body radiotherapy to osseous disease and/or the primary site. ADT was discontinued in responding patients. Outcomes of each treatment were assessed sequentially. The primary endpoint of “no evidence of disease” (NED) was defined by an undetectable PSA with noncastrate levels of testosterone at 20 months. Results: Each treatment modality contributed to the outcome: 95% of the cohort achieved an undetectable PSA with multimodal treatment, including 25% of patients after ADT alone and an additional 50% and 20% after surgery and radiotherapy, respectively. Overall, 20% of patients (95% confidence interval 3-38%) achieved the primary endpoint, which persisted for 5, 6, 27+, and 46+ months. All patients meeting the primary endpoint had been classified with M1b disease at presentation. Conclusions: Treatment directed at all sites can eliminate detectable disease in selected patients with metastatic prostate cancer. A multimodal treatment strategy inclusive of the NED endpoint for patients who present with disease that is beyond the limits of curability by any single modality should be considered to enable the evaluation of new approaches in order to prioritize large-scale testing in early stages of advanced disease.

Targeting reciprocal feedback inhibition: Apalutamide and everolimus in patients with metastatic castration-resistant prostate cancer (mCRPC)

204

Background: Studies in xenograft CRPC and PTEN-deficient prostate cancer models have shown synergistic anti-tumor activity of next-generation anti-androgens such as apalutamide when combined with PI3K/mTOR inhibitors such as everolimus. (Carver B et al., Cancer Cell 2011) The primary hypothesis of this study was that the combination of apalutamide with everolimus would overcome resistance to prior hormonal therapy with abiraterone acetate and prednisone (AAP). Methods: The primary endpoint in mCRPC patients with prior AAP was to evaluate the safety, pharmacokinetics (PK), and recommended phase 2 dose (RP2D) of fixed dose apalutamide 240 mg po qd when combined with everolimus 5 mg po qd (cohort 1, n = 3) and everolimus 10 mg po qd (cohort 2, n = 6). The plan was to expand to treat 40 patients at the RP2D. Results: Nine patients were enrolled in phase 1. The PK for the combination was consistent with historical data of either drug given as monotherapy. The most common treatment related adverse events were < = grade 2 fatigue (67%), diarrhea (56%), and anorexia (56%). In cohort 2, 1 patient had a DLT of grade 3 rash. The median time on treatment was 17 weeks (range 7-51+). The best response was SD in all 9 patients. Patients came off study for: progression (n = 3), investigator choice (n = 3) and toxicity unrelated to treatment (n = 2). Seven patients had detectable CTCs at baseline (EPIC Sciences). One patient had a rise in CTC number that then converted to undetectable and remained on study 37 weeks. One out of 6 evaluable patients had PTEN loss in tissue at baseline (MSK IMPACT) and remained on study 12 weeks. One patient with prior AAP and enzalutamide exposure has remained on study 51+ weeks with a > 50% decline in PSA (PTEN pending). Conclusions: Although the combination of apalutamide and everolimus was safe and well tolerated, the treatment response was similar to historical data of AAP followed by apalutamide alone. (Rathkopf D et al., ASCO 2014) We elected to close this study before expansion in favor of evaluating novel AR/PI3K pathway combinations in patients who have not yet been exposed to AAP. Drug provided by Janssen and Novartis. Trial support: PCF and MSK Experimental Therapeutics Center. Clinical trial information: NCT02106507.

Clinical versus radiographic progression and overall survival for patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) from COU-AA-302

193

Background: COU-AA-302 evaluated abiraterone acetate plus prednisone (AA) vs prednisone (P) in chemotherapy-naïve mCRPC pts, with overall survival (OS) and radiographic progression-free survival (rPFS) as co-primary end points. Per study criteria, pts with radiographic progression (RAD) only were allowed to continue treatment, while those with unequivocal clinical progression (UCP) only were not, and were censored for rPFS. We evaluated the clinical significance of survival outcomes for pts with UCP only vs RAD only from the prospective COU-AA-302 trial. Methods: UCP was defined per protocol as ≥ 1 of the following: initiation of chronic opiates, ECOG performance status (PS) decline to ≥ 3, or initiation of chemotherapy, palliative radiation therapy, or surgery. OS was evaluated for each type of progression using Cox proportional hazard models. Results: 500 (92%) pts in the AA arm and 540 (100%) in the P arm discontinued study treatment. Of the 736 pts who discontinued treatment for a protocol-defined reason, 280 (38%) discontinued for UCP only, 332 (45%) for RAD only, and 124 (17%) for both UCP and RAD. Clinical events cited as the reason for discontinuation for UCP (AA vs P arm) included pain requiring opiates (22% vs 25%), ECOG PS ≥ 3 (4% vs 5%), and initiation of chemotherapy (50% vs 53%), radiation therapy (36% vs 27%) and surgery (3% vs 5%). UCP only pts had shorter median OS compared with RAD only pts (Table). Conclusions: UCP is a criterion used as an indicator for a censored event, yet appears to confer inferior survival relative to RAD. The high frequency of UCP implies that it may be an important determinant of clinical outcome. The events that drive UCP should be defined as part of the development of more informative interim trial end points, in line with the PCWG3-proposed “no longer clinically benefitting” outcome measure, which captures pts with UCP. Clinical trial information: NCT00887198. [Table: see text]

Single cell phenogenomic subtyping of circulating tumor cells (CTCs) identify intercellular tumor heterogeneity (het) and multiple resistance mechansisms in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

139

Background: Genomic profiling of metastatic tumors can identify mCRPC pts w/ “actionable” targets. However, responses from this approach are infrequent and not durable, broadly attributed to intra-tumor and intrer-cellular het. We sought to understand relationships between single CTC phenotypic and genomic patterns present when starting ARSi or taxane therapy (Tx) to develop more effective biomarker-directed treatment approaches. Methods: 9225 CTCs from 319 blood samples from 179 mCRPC pts were detected and digital phenotypically profiled using the Epic Sciences platform. Unsupervised clustering revealed 15 phenotypic CTC subtypes based on digital pathology features (Type ‘A’-‘O’). Phenotypic diversity was determined by a Shannon index of these subtypes in pt samples. Next, 856 CTCs representing each subtype were individually whole genome sequenced for copy number variation and genomic instability, to define phenogenomic single cell profile and taxonomy. Tx outcomes were associated with CTC profiles. Results: Pre-therapy identification of certain CTC phenotypic subtypes was associated with poor overall survival (OS) following ARSi and/or taxanes. 5/15 subtypes existed primarily in pts w/ high CTC het (84-94%, Bonferroni adjusted p < 0.05, permutation test), and linked to amp of AR and cMYC, and loss of TP53 and PTEN. Clusters of genomic events were linked to phenotypic features (i.e. small cell CTC w/AuroraK & nMYC amp) and provide single cell phenogenomic associations with pathways such as AR/PTEN feedback and DNA repair machinery. Conclusions: Presence ofspecific CTC subtypes was associated w/ poor survival on ARSi and/or taxanes and may inform Tx selection. Identifying CTC subtypes present in high het samples can provide insight into individual pt disease evolution and potential approaches to maximize benefit. Longitudinal monitoring of CTC phenogenomics is being studied in novel Tx trials.[Table: see text]

Incidence of periprostatic white adipose tissue inflammation in men with prostate cancer

63

Background: Obesity, a common cause of chronic inflammation, is associated with an increased risk of high grade, lethal prostate cancer (PC) and poor outcomes. The existence or clinical importance of periprostatic white adipose tissue inflammation (WATi) in patients (pts) with PC has not been previously described. We examined the relationships among periprostatic WATi and 1) tumor clinicopathologic features, and 2) host factors including age, body mass index (BMI), and circulating metabolic factors. Methods: Periprostatic WAT was collected prospectively from men with PC undergoing radical prostatectomy. WATi was defined by the presence of dead/dying adipocytes surrounded by macrophages forming crown-like structures (CLS). Tumor characteristics and host factors were measured. Wilcoxon rank-sum, Chi-square, or Fisher’s exact tests were used to examine the relationship between WATi and tumor and host characteristics. Results: From 11/2011-8/2015, periprostatic WAT was obtained from 169 pts (median age 62 years, range: 39 -77). Fasting blood samples were collected from 154 pts. CLS were present in 84 (49.7%) of pts. Presence of CLS was associated with higher median BMI (P = 0.02); 40/65 (61.5%) obese pts, 36/83 (43.4 %) overweight pts, and 8/21 (38.1 %) normal weight pts had CLS. Pts with CLS were more likely to have high grade prostate cancer (Gleason grade group IV/V, P = 0.02), larger adipocytes (P = 0.004), and positive surgical margins at the time of surgery (P = 0.04). WATi correlated with higher circulating levels of insulin, triglycerides, and leptin/adiponectin ratio, and lower high density lipoprotein cholesterol, compared to pts without WATi (P’s < 0.05). Conclusions: Periprostatic WATi is common in men with PC. It is associated with high grade PC and alterations in systemic factors that contribute to PC development and progression. Periprostatic WATi may represent a therapeutic target for improving PC risk and outcomes.

Safety and Antitumor Activity of Apalutamide (ARN-509) in Metastatic Castration-Resistant Prostate Cancer with and without Prior Abiraterone Acetate and Prednisone

Purpose: To evaluate the efficacy of apalutamide before or after treatment with abiraterone acetate and prednisone (AAP) in patients with progressive metastatic castration-resistant prostate cancer (mCRPC).Experimental Design: Two cohorts were studied: AAP-naïve and post-AAP patients who had received ≥6 months of AAP. Patients had progressive mCRPC per rising prostate-specific antigen (PSA) and/or imaging, without prior chemotherapy exposure. All received apalutamide 240 mg/day. Primary endpoint was ≥50% decline in 12-week PSA according to Prostate Cancer Working Group 2 criteria. Secondary endpoints included time to PSA progression and time on treatment.Results: Forty-six patients enrolled in the AAP-naïve (n = 25) and post-AAP (n = 21) cohorts. The 12-week PSA response rate was 88% (22/25) and 22% (4/18), median time to PSA progression was 18.2 months [95% confidence interval (CI), 8.3 months-not reached) and 3.7 months (95% CI, 2.8-5.6 months), and median time on treatment 21 months (range, 2.6-37.5) and 4.9 months (range, 1.3-23.2), for the AAP-naïve and post-AAP cohorts, respectively. Eighty percent (95% CI, 59-93) and 64% (95% CI, 43-82) of AAP-naïve and 43% (95% CI, 22-66) and 10% (95% CI, 1-30) of post-AAP patients remained on treatment for 6+ and 12+ months, respectively. Common treatment-emergent adverse events in both cohorts were grade 1 or 2 fatigue, diarrhea, nausea, and abdominal pain.Conclusions: Apalutamide was safe, well tolerated, and demonstrated clinical activity in mCRPC, with 80% of AAP-naïve and 43% of post-AAP patients, remaining on treatment for 6 months or longer. Clin Cancer Res; 23(14); 3544-51. ©2017 AACR.

Association of AR-V7 on Circulating Tumor Cells as a Treatment-Specific Biomarker With Outcomes and Survival in Castration-Resistant Prostate Cancer

Importance

A critical decision in the management of metastatic castration-resistant prostate cancer (mCRPC) is when to administer an androgen receptor signaling (ARS) inhibitor or a taxane.

Objective

To determine if pretherapy nuclear androgen-receptor splice variant 7 (AR-V7) protein expression and localization on circulating tumor cells (CTCs) is a treatment-specific marker for response and outcomes between ARS inhibitors and taxanes.

Design, Setting, and Participants

For this cross-sectional cohort study at Memorial Sloan Kettering Cancer Center, 265 men with progressive mCRPC undergoing a change in treatment were considered; 86 were excluded because they were not initiating ARS or taxane therapy; and 18 were excluded for processing time constraints, leaving 161 patients for analysis. Between December 2012 and March 2015, blood was collected and processed from patients with progressive mCRPC immediately prior to new line of systemic therapy. Patients were followed up to 3 years.

Main Outcomes and Measures

Prostate-specific antigen (PSA) response, time receiving therapy, radiographic progression-free survival (rPFS), and overall survival (OS).

Results

Overall, of 193 prospectively collected blood samples from 161 men with mCRPC, 191 were evaluable (128 pre-ARS inhibitor and 63 pretaxane). AR-V7-positive CTCs were found in 34 samples (18%), including 3% of first-line, 18% of second-line, and 31% of third- or greater line samples. Patients whose samples had AR-V7-positive CTCs before ARS inhibition had resistant posttherapy PSA changes (PTPC), shorter rPFS, shorter time on therapy, and shorter OS than those without AR-V7-positive CTCs. Overall, resistant PTPC were seen in 65 of 112 samples (58%) without detectable AR-V7-positive CTCs prior to ARS inhibition. There were statistically significant differences in OS but not in PTPC, time on therapy, or rPFS for patients with or without pretherapy AR-V7-positive CTCs treated with a taxane. A multivariable model adjusting for baseline factors associated with survival showed superior OS with taxanes relative to ARS inhibitors when AR-V7-positive CTCs were detected pretherapy (hazard ratio, 0.24; 95% CI, 0.10-0.57; P = .035).

Conclusions and Relevance

The results validate CTC nuclear expression of AR-V7 protein in men with mCRPC as a treatment-specific biomarker that is associated with superior survival on taxane therapy over ARS-directed therapy in a clinical practice setting. Continued examination of this biomarker in prospective studies will further aid clinical utility.

Clinical outcomes and survival surrogacy studies of prostate-specific antigen declines following enzalutamide in men with metastatic castration-resistant prostate cancer previously treated with docetaxel

BACKGROUND

In the AFFIRM trial, enzalutamide significantly increased overall survival (OS) for men with metastatic castration‐resistant prostate cancer (mCRPC) after chemotherapy versus placebo and significantly decreased prostate‐specific antigen (PSA) levels. The goal of this post hoc analysis was to associate levels of PSA decline from baseline after enzalutamide with clinical outcomes in the postchemotherapy mCRPC setting.

METHODS

Men in the AFFIRM trial (n = 1199) were grouped by maximal PSA decline in the first 90 days of treatment. Kaplan‐Meier estimates evaluated the association of defined PSA changes from baseline with OS, progression‐free survival (PFS), radiographic PFS (rPFS), and pain response. Each PSA decline category was assessed for OS surrogacy using Prentice criteria, proportion of treatment effect explained (PTE), and proportion of variation explained.

RESULTS

Men treated with enzalutamide had improved OS (hazard ratio, 0.63; P < .001) and higher rates of PSA decline (odds ratio, >19.0; P < .001) versus placebo. PSA declines of any, ≥30%, ≥50%, and ≥90% with enzalutamide were strongly associated with greater OS, PSA PFS, rPFS (P < .001), and pain response (P < .026) versus PSA increase/no decline. Any, ≥30%, and ≥50% declines in PSA resulted in the PTE range of 1.07‐1.29, where treatment was no longer significant after adjustment for decline measures (P > .20).

CONCLUSIONS

PSA declines of any, ≥30%, and ≥50% following enzalutamide were associated with greater clinical and pain response and improvements in PFS and OS. Surrogacy of PSA decline for OS was not fully established, possibly due to lack of PSA declines with placebo, and discordant results between PSA and imaging responses over time, and because some declines were not durable due to rapid resistance development. However, a lack of PSA decline by 90 days following enzalutamide treatment was a poor prognosis indicator in this setting. Conclusions from sensitivity analyses of maximal PSA decline from baseline over the entire treatment period are consistent with PSA declines restricted to the first 90 days. Cancer 2017;123:2303–2311. © 2017 American Cancer Society.

A post hoc analysis of the randomized, double‐blind AFFIRM trial revealed that postenzalutamide prostate‐specific antigen declines of any, ≥30%, and ≥50% are associated with greater clinical and pain response. The decline criteria explain a large proportion of treatment effect on survival improvements but do not fulfill the criteria for surrogacy.

Nuclear-specific AR-V7 Protein Localization is Necessary to Guide Treatment Selection in Metastatic Castration-resistant Prostate Cancer

BACKGROUND

Circulating tumor cells (CTCs) expressing AR-V7 protein localized to the nucleus (nuclear-specific) identify metastatic castration-resistant prostate cancer (mCRPC) patients with improved overall survival (OS) on taxane therapy relative to the androgen receptor signaling inhibitors (ARSi) abiraterone acetate, enzalutamide, and apalutamide.

OBJECTIVE

To evaluate if expanding the positivity criteria to include both nuclear and cytoplasmic AR-V7 localization ("nuclear-agnostic") identifies more patients who would benefit from a taxane over an ARSi.

DESIGN, SETTING, AND PARTICIPANTS

The study used a cross-sectional cohort. Between December 2012 and March 2015, 193 pretherapy blood samples, 191 of which were evaluable, were collected and processed from 161 unique mCRPC patients before starting a new line of systemic therapy for disease progression at the Memorial Sloan Kettering Cancer Center. The association between two AR-V7 scoring criteria, post-therapy prostate-specific antigen (PSA) change (PTPC) and OS following ARSi or taxane treatment, was explored. One criterion required nuclear-specific AR-V7 localization, and the other required an AR-V7 signal but was agnostic to protein localization in CTCs.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSES

Correlation of AR-V7 status to PTPC and OS was investigated. Relationships with survival were analyzed using multivariable Cox regression and log-rank analyses.

RESULTS AND LIMITATIONS

A total of 34 (18%) samples were AR-V7-positive using nuclear-specific criteria, and 56 (29%) were AR-V7-positive using nuclear-agnostic criteria. Following ARSi treatment, none of the 16 nuclear-specific AR-V7-positive samples and six of the 32 (19%) nuclear-agnostic AR-V7-positive samples had ≥50% PTPC at 12 weeks. The strongest baseline factor influencing OS was the interaction between the presence of nuclear-specific AR-V7-positive CTCs and treatment with a taxane (hazard ratio 0.24, 95% confidence interval 0.078-0.79; p=0.019). This interaction was not significant when nuclear-agnostic criteria were used.

CONCLUSIONS

To reliably inform treatment selection using an AR-V7 protein biomarker in CTCs, nuclear-specific localization is required.

PATIENT SUMMARY

We analyzed outcomes for patients with metastatic castration-resistant prostate cancer on androgen receptor signaling inhibitors and standard chemotherapy. Patients with circulating tumor cells that had AR-V7 protein in the cellular nuclei were very likely to survive longer on taxane-based chemotherapy, and tests unable to distinguish where the protein is located in the cell are not as predictive of benefit.

A Pilot Study of a Multimodal Treatment Paradigm to Accelerate Drug Evaluations in Early-stage Metastatic Prostate Cancer

OBJECTIVE

To evaluate a multimodal strategy aimed at treating all sites of disease that provides a rapid readout of success or failure in men presenting with non-castrate metastatic prostate cancers that are incurable with single modality therapy.

MATERIALS AND METHODS

Twenty selected men with oligometastatic M1a (extrapelvic nodal disease) or M1b (bone disease) at diagnosis were treated using a multimodal approach that included androgen deprivation, radical prostatectomy plus pelvic lymphadenectomy (retroperitoneal lymphadenectomy in the presence of clinically positive retroperitoneal nodes), and stereotactic body radiotherapy to osseous disease or the primary site. Outcomes of each treatment were assessed sequentially. Androgen deprivation was discontinued in responding patients. The primary end point was an undetectable prostate-specific antigen (PSA) after testosterone recovery. The goal was to eliminate all detectable disease.

RESULTS

Each treatment modality contributed to the outcome: 95% of the cohort achieved an undetectable PSA with multimodal treatment, including 25% of patients after androgen deprivation alone and an additional 50% and 20% after surgery and radiotherapy, respectively. Overall, 20% of patients (95% confidence interval: 3%-38%) achieved the primary end point, which persisted for 5, 6, 27+ , and 46+ months. All patients meeting the primary end point had been classified with M1b disease at presentation.

CONCLUSION

A sequentially applied multimodal treatment strategy can eliminate detectable disease in selected patients with metastatic spread at diagnosis. The end point of undetectable PSA after testosterone recovery should be considered when evaluating new approaches to rapidly set priorities for large-scale testing in early metastatic disease states and to shift the paradigm from palliation to cure.

Phase 1/2 multiple ascending dose trial of the prostate-specific membrane antigen-targeted antibody drug conjugate MLN2704 in metastatic castration-resistant prostate cancer

BACKGROUND

This phase 1/2 study evaluated the dose-limiting toxicity and maximum tolerated dose of MLN2704, a humanized monoclonal antibody MLN591 targeting prostate-specific membrane antigen, linked to the maytansinoid DM1 in patients with progressive metastatic castration-resistant prostate cancer.

PATIENTS AND METHODS

A total of 62 patients received MLN2704 at ascending doses on 4 schedules: weekly (60, 84, 118, and 165mg/m²; 12 patients); every 2 weeks (120, 168, 236, and 330mg/m²; 15 patients); every 3 weeks (330 and 426mg/m²; 18 patients); and on days 1 and 15 of a 6-week schedule (6-week cycle, 330mg/m²; 17 patients). The primary efficacy endpoint was a sustained ≥50% decline from baseline prostate-specific antigen (PSA) without evidence of disease progression. Toxicity, pharmacokinetics, immunogenicity, and antitumor activity were assessed.

RESULTS

Neurotoxicity was dose-limiting. Overall, 44 patients (71%) exhibited peripheral neuropathy: 6 (10%) had grade 3/4. Neurotoxicity rates remained high despite increasing the dosing interval to 3 (13 of 14; one grade 3) and 6 weeks (16 of 17; three grade 3). MLN2704 pharmacokinetics were dose-linear. Rapid deconjugation of DM1 from the conjugated antibody was seen. In all, 5 patients (8%) experienced ≥50% decline in PSA; 5 (8%) had PSA stabilization lasting≥90 days. Only 2 of 35 patients on the 3- and 6-week schedules achieved a PSA decline of >50%.

CONCLUSIONS

MLN2704 has limited activity in metastatic castration-resistant prostate cancer. Disulfide linker lability and rapid deconjugation lead to neurotoxicity and a narrow therapeutic window.

The Added Value of Circulating Tumor Cell Enumeration to Standard Markers in Assessing Prognosis in a Metastatic Castration-Resistant Prostate Cancer Population

Purpose: Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease for which better prognostic models for survival are needed. We examined the added value of circulating tumor cell (CTC) enumeration relative to common prognostic laboratory measures from patients with CRPC.Methods: Utility of CTC enumeration as a baseline and postbaseline prognostic biomarker was examined using data from two prospective randomized registration-directed trials (COU-AA-301 and ELM-PC4) within statistical models used to estimate risk for survival. Discrimination and calibration were used to measure model predictive accuracy and the added value for CTC enumeration in the context of a Cox model containing albumin, lactate dehydrogenase (LDH), PSA, hemoglobin, and alkaline phosphatase (ALK). Discrimination quantifies how accurately a risk model predicts short-term versus long-term survivors. Calibration measures the closeness of actual survival time to the predicted survival time.Results: Adding CTC enumeration to a model containing albumin, LDH, PSA, hemoglobin, and ALK ("ALPHA") improved its discriminatory power. The weighted c-index for ALPHA without CTCs was 0.72 (SE, 0.02) versus 0.75 (SE, 0.02) for ALPHA + CTCs. The increase in discrimination was restricted to the lower-risk cohort. In terms of calibration, adding CTCs produced a more accurate model-based prediction of patient survival. The absolute prediction error for ALPHA was 3.95 months (SE, 0.28) versus 3.75 months (SE, 0.22) for ALPHA + CTCs.Conclusions: Addition of CTC enumeration to standard measures provides more accurate assessment of patient risk in terms of baseline and postbaseline prognosis in the mCRPC population. Clin Cancer Res; 23(8); 1967-73. ©2016 AACR.

Enzalutamide in castration-resistant prostate cancer patients with visceral disease in the liver and/or lung: Outcomes from the randomized controlled phase 3 AFFIRM trial

BACKGROUND

Patients with metastatic castration-resistant prostate cancer (mCRPC) and visceral metastases have a worse prognosis than those with nonvisceral metastases. Treatment with the androgen receptor inhibitor enzalutamide in the phase 3 AFFIRM trial led to significant improvements in outcomes for patients with mCRPC. For the current report, the authors analyzed the efficacy of enzalutamide among patients from the AFFIRM trial who had visceral disease.

METHODS

Patients who had liver and/or lung metastases at baseline were selected for prespecified overall survival (OS) and exploratory post hoc analyses, including prostate-specific antigen (PSA) response and the time to PSA and radiographic progression.

RESULTS

In patients who had liver metastases (n = 92), enzalutamide was associated with a lower risk of radiographic progression (hazard ratio [HR], 0.645; 95% confidence interval [CI], 0.413-1.008), improved 12-month OS (37.7% vs 20.6%) and radiographic progression-free survival (rPFS) (11.6% vs 3.0%) rates, and higher PSA response rates (35.1% vs 4.8%) compared with placebo. Enzalutamide-treated patients who had lung metastases (n = 104) had improved median OS (HR, 0.848; 95% CI, 0.510-1.410), a substantially reduced risk of radiographic progression (HR, 0.386; 95% CI, 0.259-0.577), improved 12-month OS (65.1% vs 55.3%) and rPFS (30.9% vs 8.2%) rates, increased time to PSA progression (HR, 0.358; 95% CI, 0.204-0.627), and a better PSA response rate (52.1% vs 4.9%) compared with those who received placebo. No increase in treatment-related adverse events was observed for the visceral metastases cohort compared with the nonvisceral metastases cohort.

CONCLUSIONS

Across multiple endpoints, patients who have visceral metastases have better outcomes with enzalutamide than with placebo. Cancer 2017;123:253-262. © 2016 American Cancer Society.

Improving the Decision to Pursue a Phase 3 Clinical Trial by Adjusting for Patient-Specific Factors in Evaluating Phase 2 Treatment Efficacy Data

Phase 2 clinical trials are undertaken to provide evidence of treatment efficacy and safety. A test statistic that accounts for individual patient risk in the patient population is proposed and applied to a phase 2 clinical trial for castrate metastatic prostate cancer. The test statistic is computed to compare, for each patient, the observed 2-year survival outcome to the predicted 2-year survival probability. A logistic regression model, developed using historical data in the same patient population, is used to adjust for patient risk in predicting the 2-year survival probability. Goodness-of-fit procedures are performed to ensure that a proper model is fit to the data. The test result is compared to the score test, the binomial exact test, and Fisher's exact test, all of which use the average 2-year survival probability in the population as the parameter of interest. The results demonstrate the benefit of risk adjustment in determining treatment efficacy in a single-arm phase 2 trial. By adjusting for patient risk, this method can provide a more precise assessment of phase 2 treatment efficacy, thereby improving the decision whether to proceed to a phase 3 clinical trial.

First-in-Human Imaging with 89Zr-Df-IAB2M Anti-PSMA Minibody in Patients with Metastatic Prostate Cancer: Pharmacokinetics, Biodistribution, Dosimetry, and Lesion Uptake

We conducted a phase I dose-escalation study with ⁸⁹Zr-desferrioxamine-IAB2M (⁸⁹Zr-IAB2M), an anti-prostate-specific membrane antigen minibody, in patients with metastatic prostate cancer.

METHODS

Patients received 185 MBq (5 mCi) of ⁸⁹Zr-IAB2M and Df-IAB2M at total mass doses of 10 (n = 6), 20 (n = 6), and 50 mg (n = 6). Whole-body and serum clearance, normal-organ and lesion uptake, and radiation absorbed dose were estimated, and the effect of mass escalation was analyzed.

RESULTS

Eighteen patients were injected and scanned without side effects. Whole-body clearance was monoexponential, with a median biologic half-life of 215 h, whereas serum clearance showed biexponential kinetics, with a median biologic half-life of 3.7 (12.3%/L) and 33.8 h (17.9%/L). The radiation absorbed dose estimates were 1.67, 1.36, and 0.32 mGy/MBq to liver, kidney, and marrow, respectively, with an effective dose of 0.41 mSv/MBq (1.5 rem/mCi). Both skeletal and nodal lesions were detected with ⁸⁹Zr-IAB2M, most visualized by 48-h imaging.

CONCLUSION

⁸⁹Zr-IAB2M is safe and demonstrates favorable biodistribution and kinetics for targeting metastatic prostate cancer. Imaging with 10 mg of minibody mass provides optimal biodistribution, and imaging at 48 h after injection provides good lesion visualization. Assessment of lesion targeting is being studied in detail in an expansion cohort.

Inherited DNA-Repair Gene Mutations in Men with Metastatic Prostate Cancer

BACKGROUND

Inherited mutations in DNA-repair genes such as BRCA2 are associated with increased risks of lethal prostate cancer. Although the prevalence of germline mutations in DNA-repair genes among men with localized prostate cancer who are unselected for family predisposition is insufficient to warrant routine testing, the frequency of such mutations in patients with metastatic prostate cancer has not been established.

METHODS

We recruited 692 men with documented metastatic prostate cancer who were unselected for family history of cancer or age at diagnosis. We isolated germline DNA and used multiplex sequencing assays to assess mutations in 20 DNA-repair genes associated with autosomal dominant cancer-predisposition syndromes.

RESULTS

A total of 84 germline DNA-repair gene mutations that were presumed to be deleterious were identified in 82 men (11.8%); mutations were found in 16 genes, including BRCA2 (37 men [5.3%]), ATM (11 [1.6%]), CHEK2 (10 [1.9% of 534 men with data]), BRCA1 (6 [0.9%]), RAD51D (3 [0.4%]), and PALB2 (3 [0.4%]). Mutation frequencies did not differ according to whether a family history of prostate cancer was present or according to age at diagnosis. Overall, the frequency of germline mutations in DNA-repair genes among men with metastatic prostate cancer significantly exceeded the prevalence of 4.6% among 499 men with localized prostate cancer (P<0.001), including men with high-risk disease, and the prevalence of 2.7% in the Exome Aggregation Consortium, which includes 53,105 persons without a known cancer diagnosis (P<0.001).

CONCLUSIONS

In our multicenter study, the incidence of germline mutations in genes mediating DNA-repair processes among men with metastatic prostate cancer was 11.8%, which was significantly higher than the incidence among men with localized prostate cancer. The frequencies of germline mutations in DNA-repair genes among men with metastatic disease did not differ significantly according to age at diagnosis or family history of prostate cancer. (Funded by Stand Up To Cancer and others.).

Abstract 4954: Nuclear localized AR-V7 protein as a predictive biomarker for treatment selection in metastatic castration resistant prostate cancer (mCRPC)

Background: A critical decision in the management of patients (pts) with mCRPC is when to administer an androgen receptor signaling (ARS) directed or a taxane therapy. The detection of AR-V7 mRNA in CTCs has been shown to predict for resistance to ARS,but not to taxane chemotherapy. We evaluated the relationship between AR-V7 protein expression and localization on CTCs to treatment outcomes in a separate, larger cohort as a predictive biomarker for clinical decision making.

Methods: 193 prospectively collected blood samples from 161 unique pts with progressive mCRPC about to start an ARS or taxane therapy were evaluated with an Epic Sciences CTC immunoflorescent assay that assesses CTC AR-V7 protein expression and localization in individual

cells. Associations between the presence AR-V7(+) CTCs pre-therapy and anti-tumor effects post-therapy included prostate-specific antigen (PSA) changes, radiographic progression free survival (rPFS), time on therapy, and overall survival (OS).

Results: 130 pre-ARS inhibitor and 63 pre-taxane samples were assessed of which 191 (99%) were evaluable. AR-V7(+) CTCs were found in 34 (18%) samples including 3% of the 1st, 18% of the 2nd and 31% of the 3rd+ line baseline pre-therapy samples. Patients with AR-V7 positive CTCs in a pre-ARS sample showed no PSA response and had shorter rPFS, time on therapy, and OS than those without AR-V7(+) CTCs. PSA resistance to ARS was also seen in 65 of 112 (58%) of the AR-V7(-) samples. There was no association between PSA response, rPFS, and time on therapy between AR-V7(+) and AR-V7(-) pts treated with taxane therapy. In a multivariate model adjusting for age, type of therapy, line of therapy, and pre-therapy LDH, Hgb, and presence of visceral metastasis, AR-V7(+) pts had a superior OS on taxane therapy relative to ARS (HR: 0.242, CI: 0.103 to 0.569, p = 0.0350). Conclusions: The results validate the expression of the AR-V7 protein in the nucleus of CTCs in men with mCRPC as a treatment specific biomarker that predicts resistance to ARS inhibitor therapy and separately, clinical benefit with taxane therapy over ARS-directed therapy in a clinical practice setting. Continued examination of this biomarker in prospective studies will further determine its clinical utility.

Citation Format: Howard I. Scher, David Lu, Nicole A. Schreiber, Jessica Louw, Ryon P. Graf, Ann Johnson, Adam Jendrisak, Glenn Heller, Richard Bambury, Herbert A. Vargas Alverez, Brigit McLaughlin, Justin Wahl, Stephanie Greene, Martin Fleisher, Ryan Dittamore. Nuclear localized AR-V7 protein as a predictive biomarker for treatment selection in metastatic castration resistant prostate cancer (mCRPC). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4954.

Abstract LB-070: Next generation sequencing of prostate cancer reveals germline and somatic alterations detected at diagnosis and at metastasis that may impact clinical decision making

Background: The TCGA and SU2C/PCF projects have allowed for the identification of molecular alterations in primary and metastatic castration-resistant prostate cancer (mCRPC), respectively, through whole exome sequencing of highly curated tissue samples. To explore the frequency of these alteration at clinical scale, we have used a next-generation sequencing assay called MSK-IMPACT that is targeted to 410 cancer-associated genes to profile the tumors and germline of patients (pts) with prostate cancer across the disease spectrum.

Methods: Prostate cancer pts enrolled on an IRB-approved protocol for tumor genomic profiling, with optional consent for germline DNA analysis. Fresh or archived fixed tumors and matched germline samples underwent targeted DNA sequencing and analysis of somatic mutations and copy number alterations (CNAs) using MSK-IMPACT. Germline analysis was performed according to ACMG guidelines for patients who consented.

Results: We successfully sequenced 300 tumors from 259 pts, including 171 primary and 129 metastatic samples, evaluated at MSKCC between 2/2014 and 8/2015. We identified actionable somatic alterations in &gt;60% of pts, including in the PI3K/AKT pathway (25% of pts), the MAP kinase pathway (5% of pts) and the Wnt pathway (15% of pts). We found that 26% of pts harbor a tumor somatic alteration in a gene involved in DNA damage repair (DDR). Of the 140 pts who consented to germline DNA analysis, germline pathogenic mutations were identified in BRCA2 (9% of pts), CHEK2 (5% of pts), ATM (2.1% of pts), and in BRCA1, PALB2 or PMS2 (&lt;1% of pts). Additional germline alterations were identified in BRIP1, NBN, JAK2, and FH totaling a 21% rate of germline pathogenic mutations. Overall, for patients who underwent germline and tumor somatic analysis, a 26% alteration frequency was identified in BRCA1/2, ATM or CHEK2 either in the germline or somatically. Furthermore, TP53 and BRCA somatic alterations found in men with metastatic disease were also detected in previously sampled matched primary tumors, suggesting that these alterations occur as early events in tumorigenesis.

Conclusions: In addition to confirming that actionable genomic alterations are common in men with advanced prostate cancer, two additional findings emerge that could influence clinical decision making in patients at the time of diagnosis with primary disease. First, we report a high frequency of germline pathogenic mutations, including in the DDR genes BRCA2/1, CHEK2 and ATM, that could impact treatment decisions (e.g., with PARP inhibitors) and screening of family members. Second, the fact that somatic TP53 and BRCA alterations are present in matched primary samples of patients who subsequently develop metastatic diseases suggests that early detection of these alterations may be prognostic.

Citation Format: Wassim Abida, Michael F. Walsh, Joshua Armenia, Joseph Vijai, Anuradha Gopalan, Ryan Brennan, Kristen Curtis, Maria Arcila, Daniel Danila, Angela Arnold, Dana Rathkopf, Michael J. Morris, Mark Robson, Susin Slovin, David Hyman, Jeremy Durack, Stephen B. Solomon, Herbert A. Vargas, Barry Taylor, Victor Reuter, David Solit, Michael F. Berger, Kenneth Offit, Charles L. Sawyers, Nikolaus Schultz, Howard I. Scher. Next generation sequencing of prostate cancer reveals germline and somatic alterations detected at diagnosis and at metastasis that may impact clinical decision making. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-070.

Small Glutamine-Rich Tetratricopeptide Repeat-Containing Protein Alpha (SGTA) Ablation Limits Offspring Viability and Growth in Mice

Small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA) has been implicated as a co-chaperone and regulator of androgen and growth hormone receptor (AR, GHR) signalling. We investigated the functional consequences of partial and full Sgta ablation in vivo using Cre-lox Sgta-null mice. Sgta(+/-) breeders generated viable Sgta(-/-) offspring, but at less than Mendelian expectancy. Sgta(-/-) breeders were subfertile with small litters and higher neonatal death (P < 0.02). Body size was significantly and proportionately smaller in male and female Sgta(-/-) (vs WT, Sgta(+/-) P < 0.001) from d19. Serum IGF-1 levels were genotype- and sex-dependent. Food intake, muscle and bone mass and adiposity were unchanged in Sgta(-/-). Vital and sex organs had normal relative weight, morphology and histology, although certain androgen-sensitive measures such as penis and preputial size, and testis descent, were greater in Sgta(-/-). Expression of AR and its targets remained largely unchanged, although AR localisation was genotype- and tissue-dependent. Generally expression of other TPR-containing proteins was unchanged. In conclusion, this thorough investigation of SGTA-null mutation reports a mild phenotype of reduced body size. The model's full potential likely will be realised by genetic crosses with other models to interrogate the role of SGTA in the many diseases in which it has been implicated.

Decline in Circulating Tumor Cell Count and Treatment Outcome in Advanced Prostate Cancer

Background

Treatment response biomarkers are urgently needed for castration-resistant prostate cancer (CRPC). Baseline and post-treatment circulating tumor cell (CTC) counts of ≥5 cells/7.5 ml are associated with poor CRPC outcome.

Objective

To determine the value of a ≥30% CTC decline as a treatment response indicator.

Design, setting, and participants

We identified patients with a baseline CTC count ≥5 cells/7.5 ml and evaluable post-treatment CTC counts in two prospective trials.

Intervention

Patients were treated in the COU-AA-301 (abiraterone after chemotherapy) and IMMC-38 (chemotherapy) trials.

Outcome measures and statistical analysis

The association between a ≥30% CTC decline after treatment and survival was evaluated using univariable and multivariable Cox regression models at three landmark time points (4, 8, and 12 wk). Model performance was evaluated by calculating the area under the receiver operating characteristic curve (AUC) and c-indices.

Results

Overall 486 patients (122 in IMMC-38 and 364 in COU-AA-301) had a CTC count ≥5 cells/7.5 ml at baseline, with 440, 380, and 351 patients evaluable at 4, 8, and 12 wk, respectively. A 30% CTC decline was associated with increased survival at 4 wk (hazard ratio [HR] 0.45, 95% confidence interval [CI] 0.36–0.56; p < 0.001), 8 wk (HR 0.41, 95% CI 0.33–0.53; p < 0.001), and 12 wk (HR 0.39, 95% CI 0.3–0.5; p < 0.001) in univariable and multivariable analyses. Stable CTC count (<30% fall or <30% increase) was not associated with a survival benefit when compared with increased CTC count. The association between a 30% CTC decline after treatment and survival was independent of baseline CTC count. CTC declines significantly improved the AUC at all time-points. Finally, in the COU-AA-301 trial, patients with CTC ≥5 cells/7.5 ml and a 30% CTC decline had similar overall survival in both arms.

Conclusions

A 30% CTC decline after treatment from an initial count ≥5 cells/7.5 ml is independently associated with CRPC overall survival following abiraterone and chemotherapy, improving the performance of a multivariable model as early as 4 wk after treatment. This potential surrogate must now be prospectively evaluated.

Patient summary

Circulating tumor cells (CTCs) are cancer cells that can be detected in the blood of prostate cancer patients. We analyzed changes in CTCs after treatment with abiraterone and chemotherapy in two large clinical trials, and found that patients who have a decline in CTC count have a better survival outcome.