Impact of Tumor-intrinsic Molecular Features on Survival and Acquired Tyrosine Kinase Inhibitor Resistance in ALK-positive NSCLC

While tyrosine kinase inhibitors (TKI) have shown remarkable efficacy in anaplastic lymphoma kinase (ALK) fusion-positive advanced non-small cell lung cancer (NSCLC), clinical outcomes vary and acquired resistance remains a significant challenge. We conducted a retrospective study of patients with ALK-positive NSCLC who had clinico-genomic data independently collected from two academic institutions (n = 309). This was paired with a large-scale genomic cohort of patients with ALK-positive NSCLC who underwent liquid biopsies (n = 1,118). Somatic co-mutations in TP53 and loss-of-function alterations in CDKN2A/B were most commonly identified (24.1% and 22.5%, respectively in the clinical cohort), each of which was independently associated with inferior overall survival (HR: 2.58; 95% confidence interval, CI: 1.62-4.09 and HR: 1.93; 95% CI: 1.17-3.17, respectively). Tumors harboring EML4-ALK variant 3 (v3) were not associated with specific co-alterations but were more likely to develop ALK resistance mutations, particularly G1202R and I1171N (OR: 4.11; P < 0.001 and OR: 2.94; P = 0.026, respectively), and had inferior progression-free survival on first-line TKI (HR: 1.52; 95% CI: 1.03-2.25). Non-v3 tumors were associated with L1196M resistance mutation (OR: 4.63; P < 0.001). EML4-ALK v3 and somatic co-alterations in TP53 and CDKN2A/B are associated with inferior clinical outcomes. v3 status is also associated with specific patterns of clinically important ALK resistance mutations. These tumor-intrinsic features may inform rational selection and optimization of first-line and consolidative therapy.

SIGNIFICANCE

In a large-scale, contemporary cohort of patients with advanced ALK-positive NSCLC, we evaluated molecular characteristics and their impact on acquired resistance mutations and clinical outcomes. Our findings that certain ALK variants and co-mutations are associated with differential survival and specific TKI-relevant resistance patterns highlight potential molecular underpinnings of the heterogenous response to ALK TKIs and nominate biomarkers that may inform patient selection for first-line and consolidative therapies.

The Clinical Implications of Reversions in Patients with Advanced Pancreatic Cancer and Pathogenic Variants in BRCA1, BRCA2, or PALB2 after Progression on Rucaparib

PURPOSE

PARP inhibitors (PARPi) provide an effective maintenance option for patients with BRCA- or PALB2-mutated pancreatic cancer. However, mechanisms of PARPi resistance and optimal post-PARPi therapeutic strategies are poorly characterized.

EXPERIMENTAL DESIGN

We collected paired cell-free DNA samples and post-PARPi clinical data on 42 patients with advanced, platinum-sensitive pancreatic cancer who were treated with maintenance rucaparib on NCT03140670, of whom 32 developed progressive disease.

RESULTS

Peripherally detected, acquired BRCA or PALB2 reversion variants were uncommon (5/30; 16.6%) in patients who progressed on rucaparib. Reversions were significantly associated with rapid resistance to PARPi treatment (median PFS, 3.7 vs. 12.5 months; P = 0.001) and poor overall survival (median OS, 6.2 vs. 23.0 months; P < 0.0001). All patients with reversions received rechallenge with platinum-based chemotherapy following PARPi progression and experienced faster progression on this therapy than those without reversion variants (real-world time-to-treatment discontinuation, 2.4 vs. 5.8 months; P = 0.004). Of the patients who progressed on PARPi and received further chemotherapy, the OS from initiation of second-line therapy was significantly lower in those with reversion variants than in those without (5.5 vs. 12.0 months, P = 0.002). Finally, high levels of tumor shedding were independently associated with poor outcomes in patients who received rucaparib.

CONCLUSIONS

Acquired reversion variants were uncommon but detrimental in a population of patients with advanced BRCA- or PALB2-related pancreatic ductal adenocarcinoma who received maintenance rucaparib. Reversion variants led to rapid progression on PARPi, rapid failure of subsequent platinum-based treatment, and poor OS of patients. The identification of such variants in the blood may have both predictive and prognostic value. See related commentary by Tsang and Gallinger, p. 5005.

Molecular heterogeneity and co-altered genes in MET-amplified ALK-positive lung cancer: Implications for MET targeted therapy

OBJECTIVES

MET amplification is a common mechanism of resistance to second- and third-generation anaplastic lymphoma kinase (ALK) inhibitors. In case series of MET-amplified ALK-rearranged (ALK + ) lung cancer, durability of responses to combinations targeting ALK and MET is variable, suggesting heterogeneity across tumors. However, little is known about the molecular composition of this subset of ALK-rearranged (ALK + ) NSCLC.

MATERIALS AND METHODS

We queried tissue and plasma databases to compile a group of > 50 specimens with ALK rearrangements and concurrent MET amplification. Fluorescence in-situ hybridization (FISH) and next-generation sequencing (NGS) were utilized to quantify the range of MET copies and describe the global molecular landscape of co-altered genes.

RESULTS

By FISH, high-level amplification (overall MET/centromere 7 probe ratio ≥ 5) was detected in 75 % of MET-amplified ALK + NSCLC tissue specimens. Intralesional heterogeneity of MET copies was observed, with high-level amplification identified even in cells from tumors with overall low-level MET amplification. Analysis of 48 MET-amplified ALK + NSCLC plasma specimens suggested that high-level amplification is rarely (17 %) detected in plasma. In both tissue and plasma, EML4-ALK variant 1 was the predominant variant (51 %) identified in MET-amplified specimens. ALK kinase domain mutations were only present in a minority of MET-amplified ALK + NSCLCs. MET-amplified ALK + NSCLC plasma specimens were enriched for TP53 mutations (81 % vs 45 %, p = 0.002), EGFR amplification (17 % vs 4 %, p < 0.001), and MYC amplification (21 % vs 3 %, p < 0.001) compared to ALK + NSCLC specimens lacking MET amplification.

CONCLUSIONS

MET-amplified, ALK + NSCLC often presents with high-level and heterogeneous amplification in tissue, seldom overlaps with ALK mutations, and frequently co-occurs with alterations associated with aggressive tumor biology.

Pan-Cancer Prevalence of Microsatellite Instability-High (MSI-H) Identified by Circulating Tumor DNA and Associated Real-World Clinical Outcomes

PURPOSE

Immune checkpoint inhibitors are approved for advanced solid tumors with microsatellite instability-high (MSI-H). Although several technologies can assess MSI-H status, detection and outcomes with circulating tumor DNA (ctDNA)-detected MSI-H are lacking. As such, we examined pan-cancer MSI-H prevalence across 21 cancers and outcomes after ctDNA-detected MSI-H.

METHODS

Patients with advanced cancer who had ctDNA testing (Guardant360) from October 1, 2018, to June 30, 2022, were retrospectively assessed for prevalence. GuardantINFORM, which includes anonymized genomic and structured payer claims data, was queried to assess outcomes. Patients who initiated new treatment within 90 days of MSI-H detection were sorted into immunotherapy included in treatment (IO) or no immunotherapy included (non-IO) groups. Real-world time to treatment discontinuation (rwTTD) and real-world time to next treatment (rwTTNT) were assessed in months as proxies of progression-free survival (PFS); real-world overall survival (rwOS) was assessed in months. Cox regression tests analyzed differences. Colorectal cancer, non-small-cell lung cancer (NSCLC), prostate cancer, gastroesophageal cancer, and uterine cancer (UC) were assessed independently; all other cancers were grouped.

RESULTS

In total, 1.4% of 171,881 patients had MSI-H detected. Of 770 patients with outcomes available, rwTTD and rwTTNT were significantly longer for patients who received IO compared with non-IO for all cancers (P ≤ .05; hazard ratio [HR] range, 0.31-0.52 and 0.25-0.54, respectively) except NSCLC. rwOS had limited follow-up for all cohorts except UC (IO 39 v non-IO 23 months; HR, 0.18; P = .004); however, there was a consistent trend toward prolonged OS in IO-treated patients.

CONCLUSION

These data support use of a well-validated ctDNA assay to detect MSI-H across solid tumors and suggest prolonged PFS in patients treated with IO-containing regimens after detection. Tumor-agnostic, ctDNA-based MSI testing may be reliable for rapid decision making.

Efficacy and Tolerability of ALK/MET Combinations in Patients With ALK-Rearranged Lung Cancer With Acquired MET Amplification: A Retrospective Analysis

Introduction

MET amplification is a potentially actionable resistance mechanism in ALK-rearranged (ALK+) lung cancer. Studies describing treatment outcomes of this molecular subgroup are lacking.

Methods

We assembled a cohort of patients with ALK+ lung cancer and acquired MET amplification (identified by tissue or plasma) who received regimens targeting both ALK and MET. Efficacy and safety were assessed using the Response Evaluation Criteria in Solid Tumors version 1.1 and Common Terminology Criteria for Adverse Events version 4.03, respectively.

Results

A total of 12 patients were included in the series. MET amplification was detected after a median of 1.5 (range 1-5) lines of therapy. Four distinct regimens were implemented to address MET amplification: crizotinib (n = 2), lorlatinib plus crizotinib (n = 6), alectinib plus capmatinib (n = 3), and alectinib plus crizotinib (n = 1). Partial responses were observed in five (42%) of 12 patients, including patients who received crizotinib (n = one of two), lorlatinib plus crizotinib (n = three of six), and alectinib plus capmatinib (n = one of three). Primary progression was observed in four patients (33%). Grades 1 to 2 peripheral edema, occurring in seven (58%) patients, was found with both crizotinib and capmatinib. One patient required dose reduction of capmatinib plus alectinib for persistent grade 2 edema. Across the regimens, one patient discontinued therapy for toxicity, specifically neurocognitive toxicity from lorlatinib plus crizotinib. At progression on ALK+ MET therapy, potential resistance mechanisms included MET copy number changes and ALK kinase domain mutations.

Conclusions

Combined ALK and MET inhibition is associated with moderate antitumor activity in patients with ALK+ NSCLC with concurrent MET amplification. Prospective studies are indicated to confirm activity and identify individuals most likely to benefit from the treatment.

Abstract P5-02-13: TRK inhibitor in a patient with metastatic triple negative breast cancer and NTRK fusions identified via cell-free DNA analysis

Introduction: Tissue-agnostic indications for targeted therapies are expanding options for patients with advanced solid tumors. The FDA approvals of the PD-1 inhibitor pembrolizumab and the TRK inhibitors larotrectinib and entrectinib provide rationale for next generation sequencing (NGS) in effectively all advanced solid tumor patients, as findings may indicate targeted therapy even in disease that may seem otherwise refractory. Here, we present the case of a post-menopausal woman with metastatic triple negative breast cancer (TNBC) who had disease progression on multiple lines of therapy prior to the identification of two actionable NTRK mutations, identified via cell-free DNA (cfDNA) and tissue-based NGS. She was subsequently started on the TRK inhibitor larotrectinib and had a marked clinical response. Case Presentation: A 64-year-old woman presented with metastatic TNBC five years after being treated for a localized breast cancer. The cancer rapidly progressed through 4 lines of therapy in the metastatic setting, including immunotherapy [atezolizumab/nab-paclitaxel (progression after 5 months)], antibody-drug conjugate-based therapy [sacituzumab govitecan (progression after 2 months)], and chemotherapy [gemcitabine/carboplatin (progression after 3 months), eribulin (progression after 2 months)]. Her CA 15-3 had also been consistently increasing to a peak of 206 IU/mL. Germline genetic testing was negative. Ultimately, NGS evaluation of cfDNA via an 83-gene assay (Guardant Health, Inc.) identified two NTRK3 fusions: an ETV6-NTRK3 fusion [mutant allele fraction (MAF) = 10.9%] associated with the rare secretory breast carcinoma, and CRTC3-NTRK3 (MAF = 3.2%), a fusion partner previously undescribed in breast cancer. Liver biopsy was sent for whole exome sequencing and RNA-seq analysis (BostonGene, Inc), which provided orthogonal confirmation of both the ETV6-NTRK3 and CRTC3-NTRK3 fusions. Review of the tumor pathology showed invasive ductal carcinoma with secretory features; this pathology and the ETV6-NTRK3 fusion were consistent with a diagnosis of secretory breast carcinoma. She was started on the TRK inhibitor larotrectinib, and she had a significant clinical and radiographic response after only two months of therapy. Recheck of her CA 15-3 showed a decrease to 48 IU/mL, the lowest level in our records. Repeat cfDNA testing showed a decrease of the ETV6-NTRK3 fusion to MAF 0.40% and the CRTC3-NTRK3 fusion to MAF 0.07%. The patient took larotrectinib for 7 months with good disease control. Unfortunately, unrelated to her therapy, she had experienced multiple fractures secondary to her existing osseous metastases, and these led to significant morbidity. She and her family elected to transition to comfort measures, after which she passed away. Discussion: In the presented case, the identification of NTRK fusions by plasma-based genotyping resulted in matched selection of genotype-directed therapy, and this otherwise refractory TNBC exhibited marked response to targeted therapy. While TNBC had historically been considered a subtype of breast cancer without targetable options, the expanding roles of NGS testing and targeted therapies are changing the paradigm. The actionability of rare genomic events such as NTRK fusions makes identifying them critical for individual patients, particularly in heterogeneous diseases such as TNBC. Tissue-agnostic targeted therapies now give reason for NGS testing in most solid tumors, as reflected in updated consensus guidelines. This case demonstrates the significant potential benefits of NGS testing in advanced and refractory cancers.

Citation Format: Jennifer C. Keenan, Arielle J. Medford, Lauren J. Oshry, Baris Boyraz, Charles S. Dai, Lesli A. Kiedrowski, Sofia Menshikova, Anna Butusova, Tasos Gogakos, Rachel Occhiogrosso, Phoebe Ryan, Jochen Lennerz, Laura M. Spring, Beverly Moy, Leif Ellisen, Aditya Bardia. TRK inhibitor in a patient with metastatic triple negative breast cancer and NTRK fusions identified via cell-free DNA analysis. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-13.

Abstract P5-02-07: Cell-free DNA detection of GATA3 mutations in metastatic hormone receptor positive breast cancer: a retrospective, observational multi-institutional analysis

Background GATA3 mutations (GATA3mut) have been reported in 10-20% of hormone receptor positive (HR+) breast cancers. It has been shown that targeting GATA3mut HR+ breast cancer with MDM2 inhibitors invokes synthetic lethality. MDM2 is an E3 ubiquitin ligase that targets p53 for degradation, and research suggests that restoring p53 by blocking MDM2 may be effective in treating GATA3mut HR+ breast cancer. One potential mechanism of this efficacy has been shown to be through the PI3K-AKT pathway. We thus sought to characterize the GATA3mut landscape in a multi-institutional cell-free DNA (cfDNA) analysis and to determine the association between GATA3mut and TP53 mutations, as well as alterations in the PI3K-AKT pathway and the impact of GATA3 on survival. Methods We analyzed cfDNA data collected at the Massachusetts General Hospital and at Washington University in St Louis via Guardant360, a next generation sequencing assay that analyzed up to 74 genes during the study period. The association of GATA3mut and co-mutations as well as number of prior therapies was estimated using Pearson’s chi-squared test for categorical variables, two-sample Wilcoxon rank-sum test for continues variables, and multivariable logistic regression. The impact of GATA3mut and GATA3 wildtype (WT) on progression-free survival (PFS) and overall survival (OS) was analyzed using multivariable Cox regression analysis, adjusting for age, number of prior therapies, visceral metastases, and de novo metastases. PFS and OS were evaluated in the overall study population, as well as in subgroups of patients that received endocrine monotherapy and chemotherapy. Results Out of 647 patients with HR+ MBC, 10% (n = 68) had non-synonymous GATA3 mutations. Among these 68 GATA3mut patients, 37% (n = 25) were mutations in exon 5, all but two of which were in the second zinc finger, and 62% (n = 42) were in exon 6. 62% (n = 42) were frameshift mutations, 20% (n = 14) were indels, and 18% (n = 12) were point mutations. Median mutant allele fraction (MAF) of GATAmut was 0.95% (range 0.03 – 30.5%). There was no statistically significant association of GATA3mut with the number of prior therapies, PR status, or the presence of ESR1, TP53, or PI3K-AKT pathway mutations. In the GATA3mut population, TP53 co-mutations (n = 21) were found with a median MAF of 0.6%. PI3K-AKT pathway alterations occurred in 47% (n=32) of GATA3mut patients (PIK3CA n = 27; AKT n = 2; PTEN n = 3). In the combined cohort, there was no significant difference in PFS or OS after adjusting for visceral metastases, de novo disease, number of prior therapies, and age. In a cohort of 80 patients that received endocrine monotherapy (GATA3 WT n = 74, GATA3mut n = 6), GATA3mut were associated with borderline worse PFS (HR 2.6; p = 0.061) and worse OS (HR 4.5; p = 0.009). There was no statistically significant difference in PFS or OS in a subgroup that received chemotherapy. Conclusions GATA3 mutations can be identified via cfDNA in patients with HR+ MBC. Co-mutations in TP53 occurred at overall low MAF. Further research is needed to characterize the functional impact of these low level TP53 co-mutations and develop therapeutic strategies to target GATA3 mutant MBC.

Citation Format: Arielle J. Medford, Marko Velimirovic, Andrzej Niemierko, Whitney L. Hensing, Andrew A. Davis, Katherine K. Clifton, Jennifer C. Keenan, Charles S. Dai, Lesli A. Kiedrowski, Ami N. Shah, Lorenzo Gerratana, Laura M. Spring, Leif Ellisen, Robert C. Doebele, Massimo Cristofanilli, Aditya Bardia. Cell-free DNA detection of GATA3 mutations in metastatic hormone receptor positive breast cancer: a retrospective, observational multi-institutional analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-07.

The identification of reversion mutations in patients with advanced pancreatic cancer and germline or somatic BRCA or PALB2 variants who were treated with maintenance rucaparib

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Background: Maintenance PARP inhibition (PARPi) extends progression-free survival and improves quality of life for patients (pts) with advanced, platinum-sensitive pancreatic cancer (PC) and BRCA or PALB2 variants. However, most will experience progression. PARPi resistance mechanisms are poorly defined in PC. Cell-free (cf)DNA analysis can detect some known classes of resistance mechanisms, like reversion mutations, and other potentially prognostic and predictive genomic features. Methods: Pts with advanced, platinum-sensitive pancreatic cancer and pathogenic germline or somatic BRCA1, BRCA2, or PALB2 variants were treated with maintenance rucaparib on clinical trial. cfDNA was collected at baseline and progression and analyzed with the GuardantOMNI 500-gene liquid biopsy. Time to event analysis was performed from index date of enrollment until endpoint (PFS, OS, and PFS2). Associations were tested by the log-rank test with adjustment. Results: The trial enrolled 42 pts, of whom 31 have progressed. cfDNA was available for 41 pts at baseline and 30 pts at progression; 88% had baseline detectable cfDNA. Two pts had baseline reversion mutations, 5 had new reversion mutations at progression. Of 21 pts who had tissue NGS, 17 pts had a KRAS variant in the tumor, 12 of whom had detectable cfDNA at either baseline or progression. Of the 41 patients with cfDNA samples, 10 pts had baseline KRAS mutations detected in plasma; an additional 10 pts had a detectable plasma KRAS mutation at progression. Outcomes are shown. Of those who had progressed, pts with acquired reversion mutations had shorter OS (p<0.001) and PFS (p = 0.018) on rucaparib than those without reversion mutations. Of those who received chemo after progression (n=23), PFS2 was shorter for pts with acquired reversions compared to those with no reversions (p = 0.038). KRAS mutation detection at baseline was observed with higher overall somatic allele fraction in cfDNA and a trend toward shorter PFS and OS. Conclusions: Acquired reversion mutations were infrequent but associated with worse outcomes. Other causes of resistance may be dominant. Detection of KRAS mutation in the peripheral blood may be associated with disease burden and clinical outcome. [Table: see text]

Plasma-only multiomic minimal residual disease (MRD) testing in 2,000 consecutive patients with colorectal cancer (CRC)

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Background: Use and impact of circulating tumor DNA (ctDNA) testing for MRD detection has been infrequently reported outside clinical trials. We report clinical use of a validated plasma-only multi-omic MRD assay in a large, unselected CRC cohort, including clinically annotated cases. Methods: The first 2,000 US patients (pts) with documented stage (stg) and Guardant Reveal MRD test results since clinical launch in Feb 2021 were queried; all tests per pt were analyzed (data cut-off: July 2022). Pts could be enrolled in a post-operative program (POP, up to 3 tests 3-16 weeks post-resection) or a surveillance program (SP, after treatment) for recurrent tests; pts could also have one-time tests. Programs were analyzed for stg II/III only. Clinical factors were extracted from test requisition forms; pts from Siteman Cancer Center had additional data extracted from medical records. Results: 1994 pts met criteria for analysis with median age of 64 (range 21-95); 1,112 (56%) were male. ctDNA was detected in 27%, with detection increasing by stg (Table). 30% of positive samples were detected by methylation only, a 43% increased detection over genomic only analysis. 505/544 positive pts had >1 test: 20% had ctDNA first detected on a subsequent test, a 25% increase when testing serially. Most stg II/III pts were tested in the SP. Stg II pts tested POP had a median turnaround time of 10 days (range 6-42); 96% had results prior to 12 weeks post-resection. In the annotated subgroup of 28 pts (65 tests), 8/28 (28%) had ctDNA detected. 13 pts had rectal- and 15 had colon cancer. 11/28 (39%) were stg II, 13 (46%) stg III, 4 (14%) stg IV. 26/28 had surgery, 7/13 rectal pts had neoadjuvant chemotherapy and/or radiation prior to ctDNA testing. 8 (29%) pts recurred. At data cut-off, assay sensitivity to predict or confirm recurrence was 80% (95%CI: 44.4-97.5%), specificity 100% (95%CI: 81.5-100%), PPV 100%, NPV 90% (95%CI:72.26-96.9%). Two pts with recurrence and negative ctDNA had their last test >6 months prior to recurrence. Testing informed clinical decision-making in 11 (39%) pts to proceed with systemic therapy (5), repeat scans sooner (2), proceed with biopsy (1), or confirm recurrence (3). Conclusions: Through real-word data, we confirm prior studies showing multi-omic plasma-only MRD testing has high sensitivity and specificity for recurrence and now show use of the assay in clinical decision-making. Notably, methylation analysis and serial testing both improved detection of MRD and impacted clinical care. These findings should continue to be studied in larger cohorts and randomized trials. [Table: see text]

Frequency and outcomes of BRAF alterations identified by liquid biopsy in metastatic non-colorectal gastrointestinal cancers

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Background: The impact of BRAF V600E, a known poor prognostic factor in metastatic colorectal cancer (CRC), has not been assessed broadly in non-CRC gastrointestinal (GI) cancers including pancreatic (PC), gastric/gastroesophageal (GC), hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). In view of recent tumor-agnostic approval of a BRAF V600E inhibitor, it is important to determine the prevalence and impact of BRAF alterations on non-CRC GI cancer patients (pts). Methods: Genomic results from pts with PC, GC, HCC, or CCA tested with Guardant360 (G360, Guardant Health) as part of clinical care from June 2019 – June 2022 were retrospectively queried. Prevalence of characterized nonsynonymous BRAF genomic alterations (GA) was analyzed; differences between cancer types was assessed using the Chi-squared test. The GuardantINFORM database with aggregated commercial payer health claims and de-identified records from over 243,000 individuals with G360 results was used to derive real-world overall survival (rwOS), reported in months, calculated from diagnosis of metastatic cancer; differences between cancer types were compared using log-rank tests. Results: 23,069 patients were included: PC:49%; GC:24%; CCA:20%; HCC:6%. Pts were more likely to be male (p<0.01). PC/HCC pts were tested more often at new diagnosis (vs at disease progression) than GC/CCA (p=0.02, p<0.01, respectively). BRAF GAs were identified in 2.9%, comparable to tissue-based datasets (MSK-IMPACT: 2.4%); 21% of BRAF GAs were V600E (0.6% prevalence overall). PC/CCA pts were more likely to have BRAF GAs than the overall cohort (p<0.01); they also had more BRAF V600E GAs (p<0.01). rwOS differed by cancer type and BRAF status (Table). Notably, CCA pts with BRAF V600E had superior rwOS compared to CCA pts without BRAF findings (p=0.02). rwOS is not reported for HCC due to small n. Conclusions: Identification of BRAF GAs and V600E in the non-CRC GI population by liquid biopsy is similar to rates observed in tissue-based testing and may be reliably used to assess BRAF status. BRAF GAs and subtypes have mixed prognostic implications on survival for PC/CCA/GC patients that warrants further exploration. [Table: see text]

Genomic landscape of advanced prostate cancer patients with BRCA1 versus BRCA2 mutations as detected by comprehensive genomic profiling of cell-free DNA

BRCA1-mutated prostate cancer has been shown to be less responsive to poly (ADP-ribose) polymerase (PARP) inhibitors as compared to BRCA2-mutated prostate cancer. The reason for this differential response is not clear. We hypothesized this differential sensitivity to PARP inhibitors may be explained by distinct genomic landscapes of BRCA1 versus BRCA2 co-segregating genes. In a large dataset of 7,707 men with advanced prostate cancer undergoing comprehensive genomic profiling (CGP) of cell-free DNA (cfDNA), 614 men harbored BRCA1 and/or BRCA2 alterations. Differences in the genomic landscape of co-segregating genes was investigated by Fisher's exact test and probabilistic graphical models (PGMs). Results demonstrated that BRCA1 was significantly associated with six other genes, while BRCA2 was not significantly associated with any gene. These findings suggest BRCA2 may be the main driver mutation, while BRCA1 mutations tend to co-segregate with mutations in other molecular pathways contributing to prostate cancer progression. These hypothesis-generating data may explain the differential response to PARP inhibition and guide towards the development of combinatorial drug regimens in those with BRCA1 mutation.

The Clinical Landscape of Cell-Free DNA Alterations in 1,671 Patients with Advanced Biliary Tract Cancer

BACKGROUND

Targeted therapies have transformed clinical management of advanced biliary tract cancer (BTC). Cell-free DNA (cfDNA) analysis is an attractive approach for cancer genomic profiling that overcomes many limitations of traditional tissue-based analysis. We examined cfDNA as a tool to inform clinical management of patients with advanced BTC and generate novel insights into BTC tumor biology.

PATIENTS AND METHODS

We analyzed next-generation sequencing data of 2,068 cfDNA samples from 1,671 patients with advanced BTC generated with Guardant360. We performed clinical annotation on a multi-institutional subset (n=225) to assess intra-patient cfDNA-tumor concordance and the association of cfDNA variant allele fraction (VAF) with clinical outcomes.

RESULTS

Genetic alterations were detected in cfDNA in 84% of patients, with targetable alterations detected in 44% of patients. FGFR2 fusions, IDH1 mutations, and BRAF V600E were clonal in majority of cases, affirming these targetable alterations as early driver events in BTC. Concordance between cfDNA and tissue for mutation detection was high for IDH1 mutations (87%) and BRAF V600E (100%), and low for FGFR2 fusions (18%). cfDNA analysis uncovered novel putative mechanisms of resistance to targeted therapies, including mutation of the cysteine residue (FGFR2 C492F) to which covalent FGFR inhibitors bind. High pre-treatment cfDNA VAF associated with poor prognosis and shorter response to chemotherapy and targeted therapy. Finally, we report the frequency of promising targets in advanced BTC currently under investigation in other advanced solid tumors, including KRAS G12C (1.0%), KRAS G12D (5.1%), PIK3CA mutations (6.8%), and ERBB2 amplifications (4.9%).

CONCLUSIONS

These findings from the largest and most comprehensive study to date of cfDNA from patients with advanced BTC highlight the utility of cfDNA analysis in current management of this disease. Characterization of oncogenic drivers and mechanisms of therapeutic resistance in this study will inform drug development efforts to reduce mortality for patients with BTC.

Variation in liquid biopsy cfDNA yield predicted by somatic mutation and clinical phenotypes across primary cancers

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Background: Liquid biopsy provides a non-invasive alternative to tissue biopsy by profiling the genetic mutations and biomarker characteristics of cell-free DNA (cfDNA) derived from primary and metastatic tumors found in patients’ peripheral blood. Previous studies have demonstrated significant variation in cfDNA and circulating tumor DNA (ctDNA) yield based on patient age, sex, primary tumor type, disease stage, and treatment regimen. Somatic mutations are a primary determinant of tumor phenotype, characterizing therapeutic sensitivity and resistance, as well as growth and metastasis rates. However, there has not been extensive investigation as to how presence of somatic mutations affect downstream cfDNA yield and ctDNA fraction. Methods: We screened 140,000 samples analyzed using Guardant360 liquid biopsy test for patient age, diagnosis, treatment, mutations, and associated cfDNA yield (from assay input of 3-10ml peripheral blood, 1 streck tube). We selected and grouped somatic mutations based on prevalence across the cohort. Estimated ctDNA fractions of cfDNA yields were made using the maximum mutant allele frequency (MAF) from among somatic mutations. Samples were organized by phenotype and cfDNA yield and ctDNA fraction was assessed across groups using the Wilcoxon and Kruskal-Wallis for bi-variate and multivariate comparisons, respectively. To understand impact of cfDNA yield variation on assay performance, group comparisons were further evaluated on samples binned by input cfDNA (< 5ng, 5-15ng, 15-30ng, > 30ng) representing cfDNA input requirement ranges current commercial liquid biopsy tests advertise. Results: We found significant yield variation in sample cfDNA and estimated ctDNA fraction between primary disease types ( Myield diff = 16.35ng, p < 0.0001), therapy histories ( Myield diff = 1.49ng, p < 0.001), and patient age groups ( Myield diff = 2.24ng, p < 0.0001), although this finding did not extend to comparisons within input yield bins. We found significant differences in cfDNA and ctDNA fraction across several common somatic mutations, adjusting for test multiplicity, with the greatest difference between TERT splice + and - patients ( Myield diff = 8.57ng, p < 0.0001). Further, we found significant and strong correlations (𝝆 > 0.8, p < 0.001) between EGFR exon 19 deletions and EGFR L858R MAF and estimated ctDNA fraction, and moderate correlation between MAF and cfDNA (𝝆 > 0.25, p < 0.001). Conclusions: Our results indicate that input cfDNA and ctDNA fraction varies by patient age, diagnosis and treatment, as well as with the presence of several common somatic mutations. The demonstrated correlation between somatic mutation presence and cfDNA yield offers a potential explanation for the broad variation of cfDNA yields within tumor and patient phenotypes, and may help inform blood collection strategies for patients with known somatic variants or diagnoses.

Silent mutations reveal therapeutic vulnerability in RAS Q61 cancers

RAS family members are the most frequently mutated oncogenes in human cancers. Although KRAS(G12C)-specific inhibitors show clinical activity in patients with cancer^1-3, there are no direct inhibitors of NRAS, HRAS or non-G12C KRAS variants. Here we uncover the requirement of the silent KRAS^G60G mutation for cells to produce a functional KRAS(Q61K). In the absence of this G60G mutation in KRAS^Q61K, a cryptic splice donor site is formed, promoting alternative splicing and premature protein termination. A G60G silent mutation eliminates the splice donor site, yielding a functional KRAS(Q61K) variant. We detected a concordance of KRAS^Q61K and a G60G/A59A silent mutation in three independent pan-cancer cohorts. The region around RAS Q61 is enriched in exonic splicing enhancer (ESE) motifs and we designed mutant-specific oligonucleotides to interfere with ESE-mediated splicing, rendering the RAS(Q61) protein non-functional in a mutant-selective manner. The induction of aberrant splicing by antisense oligonucleotides demonstrated therapeutic effects in vitro and in vivo. By studying the splicing necessary for a functional KRAS(Q61K), we uncover a mutant-selective treatment strategy for RAS^Q61 cancer and expose a mutant-specific vulnerability, which could potentially be exploited for therapy in other genetic contexts.

Use of on-therapy ctDNA monitoring in a patient with KIF5B-RET fusion positive advanced non-small cell lung cancer: a case report

Molecular characterization of non-small cell lung cancer (NSCLC) has led to marked improvements in the treatment of patients with advanced disease who harbor driver mutations, including those with alterations in the RET proto-oncogene. Liquid biopsy to detect circulating tumor DNA (ctDNA) is a clinically validated tool to identify genomic alterations in advanced NSCLC at diagnosis and disease progression. Whether ctDNA assessment can be integrated into other aspects of patient care is an area of ongoing active research. Here, we present the case of a 65-year-old female with KIF5B-RET fusion-positive advanced NSCLC who underwent on-therapy ctDNA surveillance while being treated on a phase 1b trial with the oral RET inhibitor RXDX-105. The patient initially presented with right-sided flank discomfort, with a CT scan identifying a large right lower lobe (RLL) lung mass and right-sided pleural effusion. CT-guided biopsy confirmed thyroid transcription factor 1 (TTF-1) positive lung adenocarcinoma. Subsequent video-assisted thoracoscopic surgery to assess resectability identified pleural studding, with pleural biopsy confirming advanced unresectable disease. Next-generation sequencing (NGS) of tumor tissue and peripheral blood confirmed the presence of a KIF5B-RET fusion, prompting initiation of trial therapy RXDX-105. After 1 year on therapy, ctDNA became detectable prompting early scans which identified disease progression. The patient was subsequently enrolled onto a phase II trial of the RET inhibitor pralsetinib, on which she continues to this day (2+ years) without detectable KIF5B-RET ctDNA and with an ongoing minor response [stable disease per response evaluation criteria in solid tumors (RECIST) v1.1] on imaging. This case illustrates a potential role for on-therapy ctDNA monitoring as a non-invasive method to evaluate treatment response and detect early relapse in patients with advanced NSCLC. Prospective investigation is required to clearly define the optimal integration of ctDNA testing into on-treatment surveillance in patients with advanced NSCLC.

The economic value of liquid biopsy for genomic profiling in advanced non-small cell lung cancer

Background:

Liquid biopsy (LB) can detect actionable genomic alterations in plasma circulating tumor circulating tumor DNA beyond tissue testing (TT) alone in advanced non-small cell lung cancer (NSCLC) patients. We estimated the cost-effectiveness of adding LB to TT in the Canadian healthcare system.

Methods:

A cost-effectiveness analysis was conducted using a decision analytic Markov model from the Canadian public payer (Ontario) perspective and a 2-year time horizon in patients with treatment-naïve stage IV non-squamous NSCLC and ⩽10 pack-year smoking history. LB was performed using the comprehensive genomic profiling Guardant360™ assay. Standard of care TT for each participating institution was performed. Costs and outcomes of molecular testing by LB + TT were compared to TT alone. Transition probabilities were calculated from the VALUE trial (NCT03576937). Sensitivity analyses were undertaken to assess uncertainty in the model.

Results:

Use of LB + TT identified actionable alterations in more patients, 68.5 versus 52.7% with TT alone. Use of the LB + TT strategy resulted in an incremental cost savings of $3065 CAD per patient (95% CI, 2195–3945) and a gain in quality-adjusted life-years of 0.02 (95% CI, 0.01–0.02) versus TT alone. More patients received chemo-immunotherapy based on TT with higher overall costs, whereas more patients received targeted therapy based on LB + TT with net cost savings. Major drivers of cost-effectiveness were drug acquisition costs and prevalence of actionable alterations.

Conclusion:

The addition of LB to TT as initial molecular testing of clinically selected patients with advanced NSCLC did not increase system costs and led to more patients receiving appropriate targeted therapy.

Locally Recurrent Secretory Carcinoma of the Breast with NTRK3 Gene Fusion

Enhanced understanding of the molecular events underlying oncogenesis has led to the development of "tumor-agnostic" treatment strategies, which aim to target a tumor's genomic profile regardless of its anatomic site of origin. A classic example is the translocation resulting in an ETV6-NTRK3 gene fusion, a characteristic driver of a histologically diverse array of cancers. The chimeric ETV6-NTRK3 fusion protein elicits constitutive activation of the tropomyosin receptor kinase (TRK) C protein, leading to increased cell survival, growth, and proliferation. Two TRK inhibitors, larotrectinib and entrectinib, are currently approved for use in the metastatic setting for the treatment of advanced solid tumors harboring NTRK fusions. Here we report a rare case of recurrent secretory carcinoma of the breast (SCB) with NTRK3 gene fusion. Whereas most cases of SCB represent slow-growing tumors with favorable outcomes, the case detailed here is the first to the authors' knowledge of recurrence within 1 year of surgery. We review the molecular findings and potential clinical significance. KEY POINTS: The translocation resulting in the ETV6-NTRK3 gene fusion is a known oncogenic driver characteristic of secretory carcinoma of the breast (SCB). Whereas most cases of SCB represent slow-growing tumors with favorable outcomes, the case here with ETV6-NTRK3 gene fusion had local recurrence within 1 year of surgery. Two tropomyosin receptor kinase (TRK) inhibitors, larotrectinib and entrectinib, are approved to treat NTRK fusion-positive tumors, demonstrating sustained high overall response rates in the metastatic setting. Approval of TRK inhibitors necessitates optimization of NTRK fusion detection assays, including detection with liquid biopsies.

Spectrum of FGFR2/3 Alterations in Cell-Free DNA of Patients with Advanced Urothelial Carcinoma

Detecting genomic alterations (GAs) in advanced urothelial carcinoma (aUC) can expand treatment options by identifying candidates for targeted therapies. Erdafitinib is FDA-approved for patients with platinum-refractory aUC with activating mutation or fusion in FGFR2/3. We explored the prevalence and spectrum of FGFR2/3 GAs identified with plasma cfDNA NGS testing (Guardant360) in 997 patients with aUC. FGFR2/3 GAs were detected in 201 patients (20%) with characterized activating GAs in 141 (14%). Our results indicate the Guardant360-based FGFR2/3 GA detection rate is similar to those described from previous studies employing tumor tissue testing, suggesting that plasma-based cfDNA NGS may non-invasively identify candidates for anti-FGFR targeted therapies.

Blood-based tumor mutational burden from circulating tumor DNA (ctDNA) across advanced solid malignancies using a commercially available liquid biopsy assay

3040

Background: Pembrolizumab was recently FDA approved across solid tumors for TMB scores ≥ 10mut/Mb as assessed by next-generation sequencing (NGS) of tissue (tTMB). A prior study of advanced cancer patients treated with immunotherapy found that higher somatic TMB, as defined by the 80th percentile in each histology, was associated with better overall survival. Previously, bTMB assessed by ctDNA from patients with newly diagnosed advanced NSCLC at a score of 16 mut/MB correlated with a tTMB score of 10 mut/MB. TMB levels vary by cancer type, line of treatment, and therapy received; the distribution of bTMB scores across solid tumor types has not been well characterized. Here we report the distribution of bTMB scores in patients with advanced malignancies. Methods: We queried 5,610 samples from patients with different cancer types undergoing clinical cell-free DNA testing (Guardant360; Redwood City, CA) and assessed bTMB scores from October 2020 - January 2021. bTMB score was derived via a previously described computational algorithm examining the total number of synonymous and non-synonymous SNVs and indels across a 1.0MB genomic footprint. We assessed the success rate of bTMB evaluation, overlap with microsatellite instability (MSI) status, and defined the distribution of bTMB levels across indications in this dataset. Results: bTMB score was successfully assessed in 4,275/5,610 (76.3%) samples (Table). The majority of samples (58%) were tested at disease progression as compared to initial diagnosis (42%). The median turnaround time from sample receipt to clinical reporting was 11 days and decreased to 9 days over the course of the study. For the majority of cancer types the 80th percentile TMB was ≥ 16 mut/MB tissue equivalency. Conclusions: Our analysis demonstrates the feasibility of measuring bTMB using a commercially available liquid biopsy assay. bTMB scores trended higher than tTMB previously reported in these cancer types, reflecting the ability of ctDNA to better capture tumor heterogeneity. cfDNA may allow for exploration of bTMB evolution throughout treatment. TMB should be interpreted in the context of disease, treatment, and method; these data establish a pan-cancer benchmark for bTMB which will serve as a resource for further studies.[Table: see text]

Corrigendum: Clinical Utilization Pattern of Liquid Biopsies (LB) to Detect Actionable Driver Mutations, Guide Treatment Decisions and Monitor Disease Burden During Treatment of 33 Metastatic Colorectal Cancer (mCRC) Patients (pts) at a Fox Chase Cancer Center GI Oncology Subspecialty Clinic

[This corrects the article DOI: 10.3389/fonc.2018.00652.].

Clinical Acquired Resistance to KRASG12C Inhibition through a Novel KRAS Switch-II Pocket Mutation and Polyclonal Alterations Converging on RAS-MAPK Reactivation

Mutant-selective KRAS^G12C inhibitors, such as MRTX849 (adagrasib) and AMG 510 (sotorasib), have demonstrated efficacy in KRAS ^G12C-mutant cancers, including non-small cell lung cancer (NSCLC). However, mechanisms underlying clinical acquired resistance to KRAS^G12C inhibitors remain undetermined. To begin to define the mechanistic spectrum of acquired resistance, we describe a patient with KRAS ^G12C NSCLC who developed polyclonal acquired resistance to MRTX849 with the emergence of 10 heterogeneous resistance alterations in serial cell-free DNA spanning four genes (KRAS, NRAS, BRAF, MAP2K1), all of which converge to reactivate RAS-MAPK signaling. Notably, a novel KRAS ^Y96D mutation affecting the switch-II pocket, to which MRTX849 and other inactive-state inhibitors bind, was identified that interferes with key protein-drug interactions and confers resistance to these inhibitors in engineered and patient-derived KRAS ^G12C cancer models. Interestingly, a novel, functionally distinct tricomplex KRAS^G12C active-state inhibitor RM-018 retained the ability to bind and inhibit KRAS^G12C/Y96D and could overcome resistance. SIGNIFICANCE: In one of the first reports of clinical acquired resistance to KRAS^G12C inhibitors, our data suggest polyclonal RAS-MAPK reactivation as a central resistance mechanism. We also identify a novel KRAS switch-II pocket mutation that impairs binding and drives resistance to inactive-state inhibitors but is surmountable by a functionally distinct KRAS^G12C inhibitor.See related commentary by Pinnelli and Trusolino, p. 1874.This article is highlighted in the In This Issue feature, p. 1861.

Olaparib in hormone receptor-positive, HER2-negative metastatic breast cancer with a somatic BRCA2 mutation

The oral poly(adenosine diphosphate-ribose) polymerase inhibitor olaparib is approved for the treatment of patients with human epidermal growth factor 2-negative (HER2-) metastatic breast cancer (mBC) and a germline breast cancer susceptibility gene (BRCA) mutation who have been treated with chemotherapy. This case report describes a 63-year-old postmenopausal woman with somatic BRCA2-mutated mBC who responded to olaparib treatment following multiple prior lines of therapy. The patient presented in January 2012 with locally advanced, hormone receptor-positive (HR+), HER2- BC which, despite initial response to neoadjuvant chemotherapy, recurred as bone disease in February 2014, and subsequently skin (June 2016) and liver (October 2016) metastases. A comprehensive 592-gene next-generation sequencing panel (Caris Life Sciences), performed on a skin biopsy, detected a pathogenic frameshift mutation in BRCA2 (H3154fs, c.9460delC), which was not identified in a 28-gene hereditary cancer germline analysis (Myriad Genetics, Inc.), and was therefore considered to be a somatic mutation. In January 2017, cell-free DNA (cfDNA) analysis (Guardant Health, Inc.) confirmed the BRCA2 H3154fs mutation in plasma. After several lines of chemotherapy and endocrine therapy, deriving clinical benefit from eribulin and capecitabine, the disease progressed by October 2017, and olaparib (300 mg orally twice daily) was initiated in January 2018. By April 2018, the liver lesions had shrunk by 80% and a >90% response in multiple skin lesions was noted. Clinical response was maintained for 8 months, followed by progression in the skin in September 2018. Biopsy of recurrent lesions revealed a novel BRCA2 mutation, E3152del (c.9455_9457delAGG), predicted to restore the open reading frame and presumably the mechanism of resistance to olaparib. Further likely resistance mutations were noted in subsequent cfDNA analyses. This case demonstrated a clinical response with olaparib as a later-line therapy for HR+, HER2- mBC with a somatic BRCA2 mutation.

Serial Monitoring of Circulating Tumor DNA by Next-Generation Gene Sequencing as a Biomarker of Response and Survival in Patients With Advanced NSCLC Receiving Pembrolizumab-Based Therapy

Although the majority of patients with metastatic non-small-cell lung cancer (mNSCLC) lacking a detectable targetable mutation will receive pembrolizumab-based therapy in the frontline setting, predicting which patients will experience a durable clinical benefit (DCB) remains challenging.

MATERIALS AND METHODS

Patients with mNSCLC receiving pembrolizumab monotherapy or in combination with chemotherapy underwent a 74-gene next-generation sequencing panel on blood samples obtained at baseline and at 9 weeks. The change in circulating tumor DNA levels on-therapy (molecular response) was quantified using a ratio calculation with response defined by a > 50% decrease in mean variant allele fraction. Patient response was assessed using RECIST 1.1; DCB was defined as complete or partial response or stable disease that lasted > 6 months. Progression-free survival and overall survival were recorded.

RESULTS

Among 67 patients, 51 (76.1%) had > 1 variant detected at a variant allele fraction > 0.3% and thus were eligible for calculation of molecular response from paired baseline and 9-week samples. Molecular response values were significantly lower in patients with an objective radiologic response (log mean 1.25% v 27.7%, P < .001). Patients achieving a DCB had significantly lower molecular response values compared to patients with no durable benefit (log mean 3.5% v 49.4%, P < .001). Molecular responders had significantly longer progression-free survival (hazard ratio, 0.25; 95% CI, 0.13 to 0.50) and overall survival (hazard ratio, 0.27; 95% CI, 0.12 to 0.64) compared with molecular nonresponders.

CONCLUSION

Molecular response assessment using circulating tumor DNA may serve as a noninvasive, on-therapy predictor of response to pembrolizumab-based therapy in addition to standard of care imaging in mNSCLC. This strategy requires validation in independent prospective studies.

Abstract A26: Defining VALUE: Routine liquid biopsy in NSCLC diagnosis—a Canadian trial in progress

Background: Genotyping tumor tissue in time for clinical treatment decision-making has been challenging in advanced non-small cell lung cancer (NSCLC). Next-generation sequencing (NGS) of cell-free DNA (cfDNA) obtained from blood samples may improve diagnostic testing, with faster turnaround time (TAT) and potential cost savings. This study defines the added value of cfDNA versus tumor tissue genotyping in patients with advanced NSCLC in the Canadian public health care system.

Methods: Patients with advanced non-squamous NSCLC patients at 6 cancer centers across Canada are being recruited (BC, Alberta, Ontario, Quebec). Two cohorts are included: 1) treatment-naïve patients with ≤10 pack year smoking history (N=150) and 2) patients with known oncogenic drivers (e.g., EGFR, ALK, ROS1, BRAF) that have progressed on tyrosine kinase inhibitors (N=60). Consenting patients undergo peripheral blood draw and cfDNA NGS analysis using Guardant360™ (Guardant Health), a validated assay that detects alterations in 74 known cancer-associated genes, prior to starting treatment (Cohort 1) or next line of treatment (Cohort 2). Standard-of-care (SOC) tissue profiling is completed per institutional standards. Endpoints include response, progression-free survival, time-to-treatment failure, as well as time to treatment initiation, number of actionable genomic alterations identified, result TAT, patient-reported quality of life (EQ-5D), and willingness to pay. A decision-analytic model will be developed to perform a cost-consequence analysis of cfDNA versus tissue-based diagnostics.

Results: Between February and October 3, 2019, 49 patients (32 female, 17 male) were recruited to Cohort 1 and 31 (21 female, 10 male) to Cohort 2. Forty patients in Cohort 1 (81.6%) had ≥1 alteration detected, with a total of 145 genetic alterations detected in 36 genes. Of these, 68 were actionable with FDA-approved drugs and/or clinical trials available. The most frequent actionable alterations were in EGFR (33.8%), MET Exon 14 Skipping (7.4%), and EML4-ALK fusion (2.9%). Additional alterations included TP53 (29.4%), KRAS (8.8%), PIK3CA (4.4%), and STK11 (2.9%). In Cohort 2, 29 patients (93.5%, 29/31) had ≥1 alteration detected, with a total of 130 alterations in 33 genes. The most frequent alterations were in EGFR (46.0%), TP53 (9.5%), EML4-ALK fusion (6.3%), ALK mutations (4.8%), and BRAF, BRCA2, GNAS, KRAS, MET Exon 14 Skipping, NRAS, and PTEN (each 3.2%). In samples with alterations detected, the median number of alterations/patient was 3 (range 1-17). The median time to Guardant report was 8 days (range 5-27). Mutations detected in tissue, concordance, and time to result for SOC tissue profiling will be updated, along with incremental treatment options for patients.

Conclusion: Over 86% of advanced NSCLC patients had detectable cfDNA and at least 61 had actionable mutations. Blood-based testing may be an important cost-efficient addition to tissue-based testing in lung cancer to determine optimal treatment options.

Citation Format: Jason Agulnik, Jennifer H. Law, Rosalyn Juergens, Janessa Laskin, Scott Laurie, Desiree Hao, Doreen A. Ezeife, Lisa W. Le, Lesli A. Kiedrowski, Richard B. Lanman, Natasha B. Leighl. Defining VALUE: Routine liquid biopsy in NSCLC diagnosis—a Canadian trial in progress [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr A26.

The dynamic landscape of BRCA1 reversion mutations from indel to SNV in a patient with ovarian cancer treated with PARP-inhibitors and immunotherapy

Background

Reversion mutations of somatic BRCA mutations are an important source of resistance within ovarian cancer. Furthermore, these reversion mutations are known to change over the course of treatment. Better understanding of the mechanisms leading to reversion mutations and the role of serial ctDNA collection in detecting changes to overall landscape of resistance mutations over time is needed to guide treatment in the metastatic setting.

Methods

Here we study a case of metastatic ovarian cancer undergoing multiple lines of treatment with collection of three serial ctDNA samples. These samples were analyzed by Guardant Health next generation sequencing to detect somatic alterations and their associated mutant allele frequency (MAF) as % cfDNA.

Results

Analysis of our initial ctDNA collection, taken during PARP-inhibitor therapy, revealed a nonsense BRCA-1 mutation (c. 2563C > T p. Q855∗), consistent with the BRCA 1 somatic mutation detected on tumor tissue analysis. Initial analysis also revealed a reversion mutation (c.2535_2576del) resulting in an in-frame deletion of the somatic BRCA-1 alteration. The second collection, taken while still on PARP-inhibitor therapy, re-demonstrated this indel reversion mutation along with a second indel reversion mutation (c.2546_2587del), again resulting in an in-frame deletion of the somatic BRCA-1 mutation. The final ctDNA, collected upon initiation of immunotherapy, revealed 4 novel SNV reversion mutations (c.2564A > C, c.2564A > T, c.2565G > T, and c.2565G > C). These SNV reversion mutations result in missense amino acid changes rather than insertions or deletions within the BRCA-1 somatic mutation. The previous indel reversion mutations were no longer detected.

Conclusions

This study illustrates the role of serial ctDNA analyses in the detection of resistance mutations and the dynamic nature of reversion mutations with multiple lines of treatment. While other studies have described both indels and SNVs that occur in tandem, a change in the types of reversion mutations detected across changing therapies has never before been described. Further studies regarding the unique selective pressures arising from use of multiple types of therapy is needed to fully explain this phenomenon.

Abstract P4-10-15: PIK3CA mutational analysis using cell-free DNA next-generation sequencing detects activating mutations that may be missed with targeted hot-spot testing

Background: The FDA recently approved alpelisib, in combination with fulvestrant, for HR+/HER2- PIK3CA-mutated advanced/metastatic breast cancer after trials demonstrated improved clinical outcomes with this targeted combination. The companion diagnostic, the Qiagen Therascreen, is a PCR-based kit detecting 11 single nucleotide variant (SNV) mutations limited to 3 exons in the PIK3CA gene. However, other functionally significant mutations outside these hotspots, including activating SNVs and indels, have been reported, suggesting they confer PI3K dependence and, therefore, sensitivity to PI3K inhibitors. We explored the prevalence and spectrum of PIK3CA mutations that can be identified with more comprehensive testing methods.

Methods: We queried a large commercial laboratory database of clinical genomic test results from Guardant360 (Guardant Health, Inc) plasma cell-free DNA (cfDNA) next-generation sequencing (NGS) analysis of 74 genes detecting SNVs, indels, copy number amplifications, and fusions. This assay includes full exonic sequencing of PIK3CA. Clinical genomic results from patients with a diagnosis of advanced breast cancer who had at least one genomic alteration detected by Guardant360 between 11/25/2016 - 6/8/2019 were retrospectively analyzed.

Results: 6940 eligible samples from 5549 unique patients with advanced breast cancer were identified; some patients had samples submitted at multiple timepoints. Excluding duplicate mutations from serial sampling, a total of 2761 nonsynonymous PIK3CA SNVs were identified in 2095 unique patients (38%); 2435 of these 2761 (88%) detected in 1982 patients (36%) were predicted to be activating. 353/1982 (18%) mutation positive patients had &gt;1 PIK3CA activating mutation detected. Among the 2435 activating SNVs, 626 (26%) were located outside the hotspots covered by the companion diagnostic test. These 626 occurrences included over 70 unique activating mutations, with 16 unique mutations observed in &gt;10 patients each. The most common non-hotspot mutations included E726K (117 patients), N345K (83 patients), and E453K (48 patients). Additional analysis was performed to assess for PIK3CA indels; 118 PIK3CA indels were identified in 118/5549 unique patients (2%). Predicted activating indels were identified across the PIK3CA gene, including the C2 and kinase domains and in the linking region between the adapter binding and Ras-binding domains.

Conclusions: PIK3CA mutation analysis with PCR-based hotspot testing is limited to only the most common mutations and will miss as many as one-quarter of alterations that could potentially be targeted with alpelisib, an FDA-approved PI3Ka inhibitor. While additional data may be needed to determine the clinical response from targeting these alterations, molecular data and case reports suggest that these less common PIK3CA mutations are viable targets for a PI3K inhibitor. Comprehensive NGS, including plasma-based cfDNA testing, should be considered to identify the full spectrum of patients who may respond to PI3K targeted therapies.

Citation Format: Lesli A Kiedrowski, Dejan Juric, Aaron I Hardin, Kristin S Price, Rebecca J Nagy, Carlos L Arteaga, Joyce O'Shaughnessy, Aditya Bardia, Massimo Cristofanilli, Richard B Lanman. PIK3CA mutational analysis using cell-free DNA next-generation sequencing detects activating mutations that may be missed with targeted hot-spot testing [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-10-15.

Identification of osimertinib-resistant EGFR L792 mutations by cfDNA sequencing: oncogenic activity assessment and prevalence in large cfDNA cohort

Cell-free DNA (cfDNA) next-generation sequencing has the potential to capture tumor heterogeneity and genomic evolution under treatment pressure in a non-invasive manner. Here, we report the detection of EGFR L792 mutations, a non-covalent mechanism of osimertinib resistance, using Guardant360 cfDNA testing in a patient with metastatic EGFR-mutant non-small cell lung cancer (NSCLC) whose disease progressed on osimertinib. We subsequently analyzed a large cohort of over 1800 additional patient samples harboring an EGFR T790M mutation and identified a concomitant L792 mutation in a total of 22 (1.2%) cases. In vitro functional assays demonstrated that the EGFR L858R/T790M/L792F/H mutations conferred intermediate-level resistance to osimertinib. Further understanding of potential acquired resistance mechanisms to targeted therapy may help inform treatment strategy in EGFR-mutant NSCLC.

Circulating Tumor DNA Sequencing Analysis of Gastroesophageal Adenocarcinoma

PURPOSE

Gastroesophageal adenocarcinoma (GEA) has a poor prognosis and few therapeutic options. Utilizing a 73-gene plasma-based next-generation sequencing (NGS) cell-free circulating tumor DNA (ctDNA-NGS) test, we sought to evaluate the role of ctDNA-NGS in guiding clinical decision-making in GEA.

EXPERIMENTAL DESIGN

We evaluated a large cohort (n = 2,140 tests; 1,630 patients) of ctDNA-NGS results (including 369 clinically annotated patients). Patients were assessed for genomic alteration (GA) distribution and correlation with clinicopathologic characteristics and outcomes.

RESULTS

Treatment history, tumor site, and disease burden dictated tumor-DNA shedding and consequent ctDNA-NGS maximum somatic variant allele frequency. Patients with locally advanced disease having detectable ctDNA postoperatively experienced inferior median disease-free survival (P = 0.03). The genomic landscape was similar but not identical to tissue-NGS, reflecting temporospatial molecular heterogeneity, with some targetable GAs identified at higher frequency via ctDNA-NGS compared with previous primary tumor-NGS cohorts. Patients with known microsatellite instability-high (MSI-High) tumors were robustly detected with ctDNA-NGS. Predictive biomarker assessment was optimized by incorporating tissue-NGS and ctDNA-NGS assessment in a complementary manner. HER2 inhibition demonstrated a profound survival benefit in HER2-amplified patients by ctDNA-NGS and/or tissue-NGS (median overall survival, 26.3 vs. 7.4 months; P = 0.002), as did EGFR inhibition in EGFR-amplified patients (median overall survival, 21.1 vs. 14.4 months; P = 0.01).

CONCLUSIONS

ctDNA-NGS characterized GEA molecular heterogeneity and rendered important prognostic and predictive information, complementary to tissue-NGS.See related commentary by Frankell and Smyth, p. 6893.

Analysis of cell-free circulating tumor DNA in 419 patients with glioblastoma and other primary brain tumors

Aim:

Genomically matched trials in primary brain tumors (PBTs) require recent tumor sequencing. We evaluated whether circulating tumor DNA (ctDNA) could facilitate genomic interrogation in these patients.

Methods:

Data from 419 PBT patients tested clinically with a ctDNA NGS panel at a CLIA-certified laboratory were analyzed.

Results:

A total of 211 patients (50%) had ≥1 somatic alteration detected. Detection was highest in meningioma (59%) and gliobastoma (55%). Single nucleotide variants were detected in 61 genes, with amplifications detected in ERBB2, MET, EGFR and others.

Conclusion:

Contrary to previous studies with very low yields, we found half of PBT patients had detectable ctDNA with genomically targetable off-label or clinical trial options for almost 50%. For those PBT patients with detectable ctDNA, plasma cfDNA genomic analysis is a clinically viable option for identifying genomically driven therapy options.

Clinical Utilization Pattern of Liquid Biopsies (LB) to Detect Actionable Driver Mutations, Guide Treatment Decisions and Monitor Disease Burden During Treatment of 33 Metastatic Colorectal Cancer (mCRC) Patients (pts) at a Fox Chase Cancer Center GI Oncology Subspecialty Clinic

Background: Liquid biopsy (LB) captures dynamic genomic alterations (alts) across metastatic colorectal cancer (mCRC) therapy and may complement tissue biopsy (TB). We sought to describe the utility of LB and better understand mCRC biology during therapy.

Methods: Thirty-three patients (pts) with mCRC underwent LB. We used permutation-based t-tests to assess associations between alts, and clinical variables and used Kendall's tau to measure correlations.

Results: Of 33 pts, 15 were women; 22 had colon, and the rest rectal cancer. Pts received a median of two lines of therapy before LB. Nineteen pts had limited testing on TB (RAS/RAF/TP53/APC), 11 extended NGS, and 3 no TB. Maxpct and alts correlated with CEA (p < 0.001, respectively). In 3/5 pts with serial LB, CEA correlated with maxpct trend, and CT tumor burden. In 6 pts, mutant RAS was seen in LB and not TB; 5/6 had received anti-EGFR therapy prior to LB, suggesting RAS alts developed post-therapy. In two pts RAS-mutated by TB, no RAS alts were detected on LB; these pts had low disease burden on CT at time of LB that also did not reveal APC or TP53 alts. In six patients who were KRAS wt based on TB, post anti-EGFR LB revealed subclonal KRAS mutations, likely a treatment effect. The median number of alts was higher post anti-EGFR LB (n = 12) vs. anti-EGFR nave LB (n = 22) (9.5 vs. 5.5, p = 0.059) but not statistically significant. More alts were also noted in post anti-EGFR therapy LB vs. KRAS wt anti-EGFR-nave LB (n = 6) (9.5 vs. 5) among patients with KRAS wild-type tumors, although the difference was not significant (p = 0.182).

Conclusions: LB across mCRC therapy detects driver mutations, monitors disease burden, and identifies sub-clonal alts that reflect drug resistance, tumor evolution, and heterogeneity. Interpretation of LB results is impacted by clinical context.

Validation of a Plasma-Based Comprehensive Cancer Genotyping Assay Utilizing Orthogonal Tissue- and Plasma-Based Methodologies

Purpose: To analytically and clinically validate a circulating cell-free tumor DNA sequencing test for comprehensive tumor genotyping and demonstrate its clinical feasibility.Experimental Design: Analytic validation was conducted according to established principles and guidelines. Blood-to-blood clinical validation comprised blinded external comparison with clinical droplet digital PCR across 222 consecutive biomarker-positive clinical samples. Blood-to-tissue clinical validation comprised comparison of digital sequencing calls to those documented in the medical record of 543 consecutive lung cancer patients. Clinical experience was reported from 10,593 consecutive clinical samples.Results: Digital sequencing technology enabled variant detection down to 0.02% to 0.04% allelic fraction/2.12 copies with ≤0.3%/2.24-2.76 copies 95% limits of detection while maintaining high specificity [prevalence-adjusted positive predictive values (PPV) >98%]. Clinical validation using orthogonal plasma- and tissue-based clinical genotyping across >750 patients demonstrated high accuracy and specificity [positive percent agreement (PPAs) and negative percent agreement (NPAs) >99% and PPVs 92%-100%]. Clinical use in 10,593 advanced adult solid tumor patients demonstrated high feasibility (>99.6% technical success rate) and clinical sensitivity (85.9%), with high potential actionability (16.7% with FDA-approved on-label treatment options; 72.0% with treatment or trial recommendations), particularly in non-small cell lung cancer, where 34.5% of patient samples comprised a directly targetable standard-of-care biomarker.Conclusions: High concordance with orthogonal clinical plasma- and tissue-based genotyping methods supports the clinical accuracy of digital sequencing across all four types of targetable genomic alterations. Digital sequencing's clinical applicability is further supported by high rates of technical success and biomarker target discovery. Clin Cancer Res; 24(15); 3539-49. ©2018 AACR.

Characterization of metastatic urothelial carcinoma via comprehensive genomic profiling of circulating tumor DNA

BACKGROUND

Biomarker-guided clinical trials are increasingly common in metastatic urothelial carcinoma (mUC), yet patients for whom contemporary tumor tissue is not available are not eligible. Technological advancements in sequencing have made cell-free circulating DNA (cfDNA) next-generation sequencing (NGS) readily available in the clinic. The objective of the current study was to determine whether the genomic profile of mUC detected by NGS of cfDNA is similar to historical tumor tissue NGS studies. A secondary objective was to determine whether the frequency of genomic alterations (GAs) differed between lower tract mUC (mLTUC) and upper tract mUC (mUTUC).

METHODS

Patients from 13 academic medical centers in the United States who had a diagnosis of mUC between 2014 and 2017 and for whom cfDNA NGS results were available were included. cfDNA profiling was performed using a commercially available platform (Guardant360) targeting 73 genes.

RESULTS

Of 369 patients with mUC, 294 were diagnosed with mLTUC and 75 with mUTUC. A total of 2130 GAs were identified in the overall mUC cohort: 1610 and 520, respectively, in the mLTUC and mUTUC cohorts. In the mLTUC cohort, frequently observed GAs were similar between cfDNA NGS and historical tumor tissue studies, including tumor protein p53 (TP53) (P = 1.000 and .115, respectively), AT-rich interaction domain 1A (ARID1A) (P = .058 and .058, respectively), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) (P = .058 and .067, respectively), erb-b2 receptor tyrosine kinase 2 (ERBB2) (P = .565 and .074, respectively), and fibroblast growth factor receptor 3 (FGFR3) (P = .164 and .014, respectively). No significant difference was observed with regard to the frequency of GAs between patients with mLTUC and mUTUC.

CONCLUSIONS

Among patients with mUC for whom no tumor tissue was available, cfDNA NGS was able to identify a similar profile of GAs for biomarker-driven clinical trials compared with tumor tissue. Despite the more aggressive clinical course, cases of mUTUC demonstrated a circulating tumor DNA genomic landscape that was similar to that of mLTUC. Cancer 2018;124:2115-24. © 2018 American Cancer Society.

Searching for the Kinkeepers: Historian Gender, Age, and Type 2 Diabetes Family History

Kinkeepers facilitate family communication and may be key to family medical history collection and dissemination. Middle-aged women are frequently kinkeepers. Using type 2 diabetes (T2DM) as a model, we explored whether the predicted gender and age effects of kinkeeping can be extended to family medical historians. Through a U.S. telephone survey, nondiabetic Mexican Americans (n = 385), Blacks (n = 387), and Whites (n = 396) reported family histories of T2DM. Negative binomial regressions used age and gender to predict the number of affected relatives reported. Models were examined for the gender gap, parabolic age effect, and gender-by-age interaction predicted by kinkeeping. Results demonstrated support for gender and parabolic age effects but only among Whites. Kinkeeping may have application to the study of White family medical historians, but not Black or Mexican American historians, perhaps because of differences in family structure, salience of T2DM, and/or gender roles.

Parents' Perspectives on Variants of Uncertain Significance from Chromosome Microarray Analysis

Chromosomal microarray analysis (CMA) for unexplained anomalies and developmental delay has improved diagnosis rates, but results classified as variants of uncertain significance (VUS) may challenge both clinicians and families. We explored the impact of such results on families, including parental knowledge, understanding and interpretation. Semi-structured telephone interviews were conducted with parents (N = 14) who received genetic counseling for a VUS in their child. Transcripts were analyzed through an iterative coding process. Participants demonstrated a range of recall and personal interpretation regarding whether test results provided a causal explanation for their children's health issues. Participants maintained contradictory interpretations, describing results as answers while maintaining that little clarification of their child's condition had been provided. Reported benefits included obtaining medical services and personal validation. Parents described adaptation/coping processes similar to those occurring after positive test results. Recall of terminology, including "VUS" and precise CMA abnormalities, was poor. However, most demonstrated conceptual understanding of scientific uncertainty. All participants expressed intentions to return for recommended genetics follow-up but had misconceptions about how this would occur. These results provide insight into the patient-and-family experience when receiving uncertain genomic findings, emphasize the importance of exploring uncertainty during the communication process, and highlight areas for potential attention or improvement in the clinical encounter.

Actionable exomic incidental findings in 6503 participants: challenges of variant classification

Recommendations for laboratories to report incidental findings from genomic tests have stimulated interest in such results. In order to investigate the criteria and processes for assigning the pathogenicity of specific variants and to estimate the frequency of such incidental findings in patients of European and African ancestry, we classified potentially actionable pathogenic single-nucleotide variants (SNVs) in all 4300 European- and 2203 African-ancestry participants sequenced by the NHLBI Exome Sequencing Project (ESP). We considered 112 gene-disease pairs selected by an expert panel as associated with medically actionable genetic disorders that may be undiagnosed in adults. The resulting classifications were compared to classifications from other clinical and research genetic testing laboratories, as well as with in silico pathogenicity scores. Among European-ancestry participants, 30 of 4300 (0.7%) had a pathogenic SNV and six (0.1%) had a disruptive variant that was expected to be pathogenic, whereas 52 (1.2%) had likely pathogenic SNVs. For African-ancestry participants, six of 2203 (0.3%) had a pathogenic SNV and six (0.3%) had an expected pathogenic disruptive variant, whereas 13 (0.6%) had likely pathogenic SNVs. Genomic Evolutionary Rate Profiling mammalian conservation score and the Combined Annotation Dependent Depletion summary score of conservation, substitution, regulation, and other evidence were compared across pathogenicity assignments and appear to have utility in variant classification. This work provides a refined estimate of the burden of adult onset, medically actionable incidental findings expected from exome sequencing, highlights challenges in variant classification, and demonstrates the need for a better curated variant interpretation knowledge base.