Alterations In DNA Damage Repair Genes Research Articles

Are DNA Repair Gene Alterations Associated With the Response to Platinum-Based Regimen and Immune Checkpoint Inhibitors in Patients With Solid Tumors?

We analyzed the antitumor activity of platinum-based chemotherapies and then immune checkpoint inhibitors (ICI) in all-comers patients with solid tumors having a somatic DNA damage repair gene alteration (DDR-GA) identified through a prospective precision medicine study (NCT02534649). Each DDR-GA was classified as pathogenic (Pa), probably pathogenic (PPa), and unknown pathogenicity (UPa) according to OncoKB and ClinVAR databases. Between January 2018 and May 2020, 662 patients were screened. One hundred ninety-nine tumors with DDR-GA were found in 121 (18.3%) patients. Ninety-six patients received platinum-based chemotherapy in the advanced setting. No difference in objective response rate (ORR) under platinum regimen was observed between the 3 DDR-GA groups. The only predictor of worse progression-free survival (PFS) in Cox regression was the existence of a Pa alteration compared to the UPa group: HR = 2.11 (95% CI = 1.2-3.7), P = .009. Forty-eight patients received ICI alone or in combination. We observed a significant trend in better ORR to ICI according to the DDR-GA status: 1/11 (9%) patients in UPa, 5/17 (29.4%) patients in PPa, and 9/20 (45%) patients in Pa (P = .003, Cochran-Armitage trend test), and an increased 6-month PFS probability of 11%, 44%, and 50% in the UPa, PPa, and Pa groups, respectively (P = .37, log-rank test). Overall, somatic pathogenic DDR-GAs were not associated with ORR or PFS to platinum-based chemotherapy in patients with unselected advanced solid tumors. However, DDR-GA seemed to impact ORR and PFS to ICI, paving the way for a therapeutic combination with ICI and molecules targeting the DDR mechanisms, which are currently evaluated in ongoing clinical trials.

Abstract 4531: The synergistic potential of PARP inhibitors and irinotecan in small cell lung cancer

Abstract Background: Small cell lung cancer (SCLC) is highly aggressive and associated with a poor prognosis. While effective treatment is limited after a relapse from platinum-based chemotherapy, recent research has identified novel pathway targets including DNA damage repair (DDR) pathway. Poly (ADP-ribose) polymerase inhibitors (PARPi) have been currently evaluated for their efficacy as a monotherapy and in combination with other agents, such as immunotherapy. Methods: We evaluated the efficacy of combining PARPi and irinotecan in ten SCLC cell lines with diverse genetic backgrounds in the DDR genes. After treating the cells with three different PARPi in combination with irinotecan, we assessed cell viability and the combination effects. Furthermore, we confirmed protein changes in the DDR pathway through western blotting and measured the number of apoptotic cells using Annexin V staining. Results: In our experiments, talazoparib had the most potent effect at low concentrations, while olaparib and venadaparib showed more pronounced synergistic effects (average fold change of IC50: olaparib, 1649±4049; talazoparib, 25±34.21; venadaparib, 336±596.01; see Table). The combination of talazoparib or venadaparib with irinotecan led to a reduction of IC50 values to below 10 nM in 7 out of 10 tested cell lines. Three cell lines carrying BRCA mutations displayed a strong sensitivity to PARPi, whereas no significant correlation found with alterations in other DDR genes. The combined use of both drugs increased p-chk1 and p-p53 proteins, along with apoptosis signaling. Additionally, venadaparib alone did not induce cell toxicity but significantly increased apoptosis when combined with irinotecan, even at very low concentrations. Conclusions: The combination of a PARPi with irinotecan significantly inhibited cell growth more than the use of either agent alone. Our findings indicate that clinical trials are warranted to confirm the effectiveness of combining PARPi with irinotecan in patients with SCLC. IC50 values of PARP inhibitors in SCLC cells w/or w/o irinotecan 50 Nm IC50 (nM) Olaparib Talazoparib Venadaparib BRCA or PTEN status Irinotecan 50 nM - + - + - + BRCA1 deletion NCI-H1694 5,933 148.9 52.38 2.19 >10,000 1.02 BRCA2 deletion NCI-H211 392.8 37.20 2.28 0.99 3.82 0.94 BRCA2 deletion NCI-H1048 1,704 282.7 9.74 2.36 62.01 3.02 PTEN deletion NCI-H1341 >10,000 6,880 452.9 83.9 >10,000 >10,000 PTEN deletion DMS 79 2,382 221.9 18.55 3.4 175.16 3.07 no mutation NCI-H841 5,099 6,202 529.5 380.5 >10,000 >10,000 no mutation NCI-H2029 >10,000 >10,000 478.2 56.16 >10,000 >10,000 no mutation NCI-H2227 3,407 827.5 52.03 2.17 >10,000 0.69 no mutation NCI-H146 5,094 3.31 56.11 0.86 1,295 0.93 no mutation NCI-H209 579.2 0.05 5.24 0.05 8.18 0.04 Citation Format: Songji Oh, Miso Kim, Soyeon Kim, Bhumsuk Keam, Jeonghwan Youk, Tae Min Kim, Dong-Wan Kim, Dae Seog Heo. The synergistic potential of PARP inhibitors and irinotecan in small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4531.

Rucaparib for the Treatment of Metastatic Castration-resistant Prostate Cancer Associated with a DNA Damage Repair Gene Alteration: Final Results from the Phase 2 TRITON2 Study

BackgroundInitial TRITON2 (NCT02952534) results demonstrated the efficacy of rucaparib 600 mg BID in patients with metastatic castration-resistant prostate cancer (mCRPC) associated with a BRCA1 or BRCA2 (BRCA) or other DNA damage repair (DDR) gene alteration. ObjectiveTo present the final data from TRITON2. Design, setting, and participantsTRITON2 enrolled patients with mCRPC who had progressed on one or two lines of next-generation androgen receptor–directed therapy and one taxane-based chemotherapy. Outcome measurements and statistical analysisThe primary endpoint was objective response rate (ORR; as per the modified Response Evaluation Criteria in Solid Tumor Version 1.1/Prostate Cancer Clinical Trials Working Group 3 criteria in patients with measurable disease by independent radiology review [IRR]); prostate-specific antigen (PSA) response rate (≥50% decrease from baseline [PSA50]) was a key secondary endpoint. Results and limitationsAs of July 27, 2021 (study closure), TRITON2 had enrolled 277 patients, grouped by mutated gene: BRCA (n = 172), ATM (n = 59), CDK12 (n = 15), CHEK2 (n = 7), PALB2 (n = 11), or other DDR gene (Other; n = 13). ORR by IRR was 46% (37/81) in the BRCA subgroup (95% confidence interval [CI], 35–57%), 100% (4/4) in the PALB2 subgroup (95% CI, 40–100%), and 25% (3/12) in the Other subgroup (95% CI, 5.5–57%). No patients within the ATM, CDK12, or CHEK2 subgroups had an objective response by IRR. PSA50 response rates (95% CI) in the BRCA, PALB2, ATM, CDK12, CHEK2, and Other subgroups were 53% (46–61%), 55% (23–83%), 3.4% (0.4–12), 6.7% (0.2–32%), 14% (0.4–58%), and 23% (5.0–54%), respectively. ConclusionsThe final TRITON2 results confirm the clinical benefit and manageable safety profile of rucaparib in patients with mCRPC, including those with an alteration in BRCA or select non-BRCA DDR gene. Patient summaryAlmost half of TRITON2 patients with BRCA-mutated metastatic castration-resistant prostate cancer had a complete or partial tumor size reduction with rucaparib; clinical benefits were also observed with other DNA damage repair gene alterations.

Retrospective evaluation of the value of DNA damage repair gene signature in response to platinum-based chemotherapy in advanced pancreatic ductal adenocarcinoma.

4137 Background: Mutations affecting DNA Damage Repair (DDR) genes have been associated with clinical benefits from platinum-based chemotherapy (PBC) in ovarian and breast cancer. Mutations of DDR genes, including BRCA1/2, PALB2, ATM, ATR, CHK1, or RAD51, are found in around 15% of pancreatic ductal adenocarcinoma (PDAC). Nevertheless, whether advanced PDAC patients harboring DDR gene mutations could benefit more from PBC has not been well established. In this study, we aimed to compare the prevalence of DDR gene mutations between advanced PDAC patients who benefited from PBC and those who did not. Methods: We retrospectively analyzed samples from patients with advanced PDAC who received PBC at our institution from 2008 to 2022. Patients with partial response or progression-free survival (PFS) > 6 months were considered responders, and those with progression disease as the best response were considered non-responders. Tumor molecular profiling was performed on tumor samples by Next Generation Sequencing (NGS) of DNA. Fisher’s exact test was used to compare DDR genomic alterations in responders vs. non-responders. Overall survival (OS) was defined as the time from the start of PBC to the date of death. PFS was defined as the time between the start of PBC and the first date of documented progression or death, whichever occurs first. Survival outcomes were estimated using Kaplan-Meier curves, and differences were tested using the long-rank test. Results: A total of 132 patients with advanced PDAC treated with PBC were included in this study. The median age at diagnosis was 55 years (range 27-79 years), and 71 (53.79%) patients were male. In this cohort, 88 (66.67%) patients were identified as responders. Tumor molecular profiling showed that among responders, 42 patients (47.7%) had genomic alterations in BRCA1/2 or PALB2, and 10 patients (11.3%) had alterations in other DDR genes. In contrast, only 17 patients (38.64%) showed DDR gene alternations among non-responders. Importantly, mutations in DDR genes are significantly associated with the responder group (OR=2.28; 95% CI 1.03-5.17, p=0.04). In line with these findings, patients with DDR gene mutations showed significantly longer PFS (median PFS 9.95 months) compared with patients without DDR gene mutations (median PFS 6.51 months) (HR= 0.57; 95%CI 0.39-0.85; p=0.005). Moreover, significantly longer OS was found in patients with DDR gene mutations (median OS 20.5 months) compared with those without DDR gene mutations (median OS 16.8 months) (HR=0.67; 95%CI 0.45-1; p=0.05). Conclusions: Genomic alterations in DDR genes are significantly associated with the benefit of PBC treatment in advanced PDAC patients. Our results argue in favor of using DDR genes as a decision-making tool for advanced PDAC patient stratification even before the stand-of-care chemotherapies.

Clinical implications of molecular alterations in intraductal carcinoma of the prostate.

5024 Background: Intraductal carcinoma of the prostate (IDC-P) is a recent addition to the 2016 WHO classification system and little is known about the nature of its true incidence and biology. Clinically, it has been observed to be associated with higher grade group tumors and a more aggressive disease course with a high risk of local recurrence and distant metastasis. However, the molecular underpinnings which define IDC-P are not well elucidated. Initial case series with molecular profiling have suggested an enrichment of alterations in DNA damage/repair (DDR), PI3K, WNT and MAPK pathways. We now present comprehensive molecular profiling data from the largest cohort of IDC-P reported to date in order to better characterize this relatively new histologic entity. Methods: Eligible patients included those with radical prostatectomy tumor tissue labeled as IDC-P on testing requisition with available tissue-based DNA and RNA sequencing utilizing a commercially available CLIA-certified assay (Caris Life Sciences). Prostatic tumor specimens were analyzed using NextGen DNA sequencing (NextSeq, 592 genes and NovaSeq, WES). Digitized H&E slides underwent central pathological review by a board certified pathologist (SW) specializing in genitourinary malignancies to confirm presence of intraductal histology according to the 2022 WHO classification. Results: 31 of 44 submitted cases were confirmed to be IDC-P on central review. Median age of patients was 64 yrs (range 44-79). The majority of cases (26/31 - 84%) were Grade Group 5 and all were Grade Group 3 or higher. Overall the most frequently detected alterations were in TP53 (39%), TMPRSS2 fusion (39%), FOXA1 (16%), CDK12 (10%), PIK3CA (10%), SPOP (10%), ATM (7%), AKT1 (7%) and RB1 (5%). The most commonly altered pathways were in cell cycle regulators (50%), DDR ( BRCA1/2, ATM, CDK12) (23%), and PI3K/AKT/MTOR (23%) and WNT (10%). The FOXA1 mutation rate in this cohort was higher compared to the localized prostate cancer cohort from the TCGA (16% - 5/31 vs 6% - 82/1325). In the IDC-P cohort, there were no tumors which demonstrated mismatch-repair deficiency (dMMR) or microsatellite instability and none of the profiled tumors had a high tumor mutational burden (≥10 mutations/megabase). Conclusions: This data suggests that IDC-P harbors targetable molecular alterations in DDR genes ( BRCA1/2 and CDK12) with approved targeted agents (e.g. PARP inhibitors). These findings should underscore the importance of germline and somatic mutation testing when IDC-P is identified. We also found enrichment of oncogenic FOXA1 mutations in IDC-P which are associated with prostate cancer progression, castrate-resistance and an unfavorable prognosis. Further efforts are ongoing to expand this cohort of IDC-P cases and compare them with a matched cohort of pure adenocarcinoma cases and will include analysis of key RNA expression signatures.

Analysis of Plasma Circulating Tumor DNA in Borderline Resectable Pancreatic Cancer Treated with Neoadjuvant Modified FOLFIRINOX: Clinical Relevance of DNA Damage Repair Gene Alteration Detection.

There are no reliable biomarkers to guide treatment for patients with borderline resectable pancreatic cancer (BRPC) in the neoadjuvant setting. We used plasma circulating tumor DNA (ctDNA) sequencing to search biomarkers for patients with BRPC receiving neoadjuvant mFOLFIRINOX in our phase 2 clinical trial (NCT02749136). Among the 44 patients enrolled in the trial, patients with plasma ctDNA sequencing at baseline or post-operation were included in this analysis. Plasma cell-free DNA isolation and sequencing were performed using the Guardant 360 assay. Detection of genomic alterations, including DNA damage repair (DDR) genes, were examined for correlations with survival. Among the 44 patients, 28 patients had ctDNA sequencing data qualified for the analysis and were included in this study. Among the 25 patients with baseline plasma ctDNA data, 10 patients (40%) had alterations of DDR genes detected at baseline, inclu-ding ATM, BRCA1, BRCA2 and MLH1, and showed significantly better progression-free survival than those without such DDR gene alterations detected (median, 26.6 vs. 13.5 months; log-rank p=0.004). Patients with somatic KRAS mutations detected at baseline (n=6) had significantly worse overall survival (median, 8.5 months vs. not applicable; log-rank p=0.003) than those without. Among 13 patients with post-operative plasma ctDNA data, eight patients (61.5%) had detectable somatic alterations. Detection of DDR gene mutations from plasma ctDNA at baseline was associated with better survival outcomes of pati-ents with borderline resectable pancreatic ductal adenocarcinoma treated with neoadjuvant mFOLFIRINOX and may be a prognostic biomarker.

Abstract 6102: Targeting BARD1 slows PDAC growth in vitro and in vivo and sensitizes cells to DNA damaging agents

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent malignant neoplasm of the pancreas, responsible for over 90% of pancreatic cancer cases. Despite recent therapeutic advances, the five-year overall survival rate for PDAC is only 11% and therapies remain limited. It is now known that deficiency in DNA damage repair (DDR) renders PDAC cells vulnerable to certain DNA damage agents, for example, poly (ADP-ribose) polymerase inhibitors (PARPi). Most of the DDR genes mutated in PDAC are crucial for the proper functioning of the homologous recombination repair (HRR) pathway, and loss-of-function alterations in DDR genes sensitize cells to DNA-damaging agents. Since this treatment strategy is currently limited to 5-10% of PDAC cases with known mutations in the DDR genes, it underscores a dire need to understand new therapeutic avenues and expand the PDAC patient population that could benefit from this therapeutic approach. We have recently published that BARD1 (BRCA1- Associated- Ring- Domain- 1), an obligate binding partner of BRCA1, is upregulated in PDAC cells exposed to PARPi/platinums. We found that transient inhibition of BARD1 rendered PDAC cells extremely sensitive to olaparib (PARPi)/oxaliplatin (platinum), and enhanced DNA damage. Based on these results, we created two genetic models of BARD1 inhibition and utilized these model systems to investigate if loss of BARD1 chemo-sensitizes PDAC cells to other PARPis and DNA damage agents. Doxycycline inducible shRNA and BARD1 CRISPR KO models were created to inhibit gene expression of BARD1 in PDAC cells. We first characterized these model systems to confirm the loss of BARD1 protein and mRNA expression by western blot and qRT-PCR analyses. Using colony formation and Pico green cell survival assays, we found that inhibiting BARD1 resulted in slower growth of pancreatic cancer cells in vitro. Moreover, expression of several cell cycle genes from G2-M phase was significantly decreased (p=0.05). These studies were recapitulated in a mouse xenograft subcutaneous model, where BARD1 KO and WT PDAC cells were injected subcutaneously and tumor growth was analyzed over 25-30 days. Kaplan-Meier curves were calculated and plotted using Log-rank test. We found that inhibiting BARD1 significantly (p=0.026) delayed formation of PDAC tumors in vivo. Next, we analyzed the efficacies of various DNA damaging agents when BARD1 was inhibited. Silencing or CRISPR KO of BARD1 enhanced efficacy of mitomycin C, irinotecan, as well as other PARPis, which are currently in clinical trials (rucaparib, veliparib) in vitro and lowered their IC50s. These results indicate that targeting BARD1 has the potential to benefit patients in terms of novel or improved treatments. Our ongoing and future studies will expand on these findings to understand BARD1-mediated pathway and evaluate sensitivity of multiple DNA damage agents by screening a library of > 250 compounds. Citation Format: Sohum Patel, Anoohya Arkala, Avinoam Nevler, Carolyn Coats, Charles J. Yeo, Aditi Jain. Targeting BARD1 slows PDAC growth in vitro and in vivo and sensitizes cells to DNA damaging agents. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6102.

A generalizable machine learning framework for classifying DNA repair defects using ctDNA exomes

Specific classes of DNA damage repair (DDR) defect can drive sensitivity to emerging therapies for metastatic prostate cancer. However, biomarker approaches based on DDR gene sequencing do not accurately predict DDR deficiency or treatment benefit. Somatic alteration signatures may identify DDR deficiency but historically require whole-genome sequencing of tumour tissue. We assembled whole-exome sequencing data for 155 high ctDNA fraction plasma cell-free DNA and matched leukocyte DNA samples from patients with metastatic prostate or bladder cancer. Labels for DDR gene alterations were established using deep targeted sequencing. Per sample mutation and copy number features were used to train XGBoost ensemble models. Naive somatic features and trinucleotide signatures were associated with specific DDR gene alterations but insufficient to resolve each class. Conversely, XGBoost-derived models showed strong performance including an area under the curve of 0.99, 0.99 and 1.00 for identifying BRCA2, CDK12, and mismatch repair deficiency in metastatic prostate cancer. Our machine learning approach re-classified several samples exhibiting genomic features inconsistent with original labels, identified a metastatic bladder cancer sample with a homozygous BRCA2 copy loss, and outperformed an existing exome-based classifier for BRCA2 deficiency. We present DARC Sign (DnA Repair Classification SIGNatures); a public machine learning tool leveraging clinically-practical liquid biopsy specimens for simultaneously identifying multiple types of metastatic prostate cancer DDR deficiencies. We posit that it will be useful for understanding differential responses to DDR-directed therapies in ongoing clinical trials and may ultimately enable prospective identification of prostate cancers with phenotypic evidence of DDR deficiency.

Analysis of plasma circulating tumor DNA in borderline resectable pancreatic ductal adenocarcinoma treated with neoadjuvant modified FOLFIRINOX: Clinical relevance of DNA damage repair gene alterations.

737 Background: There is no reliable biomarker to guide treatment for patient with borderline resectable pancreatic ductal adenocarcinoma (PDAC) treated with neoadjuvant modified (m)FOLFIRINOX. We investigated the role of plasma circulating tumor DNA (ctDNA) sequencing to discover potential biomarkers for patients treated with neoadjuvant mFOLFIRINOX in our phase 2 clinical trial (ClinicalTrials.gov identifier: NCT02749136). Methods: Among 44 patients enrolled in the trial, patients with plasma ctDNA analysis performed at baseline or post-operative period were included in the analysis. Plasma cell-free DNA isolation and sequencing of ctDNA were performed using the Guardant 360 assay. Association of clinical outcomes with germline or somatic mutations of DNA damage repair (DDR) genes was analyzed. Somatic alterations other than DDR genes were also analyzed to find potential biomarkers of neoadjuvant mFOLFIRINOX. Progression free-survival (PFS) was defined as time from the initiation of mFOLFIRINOX to disease progression or any cause of death. Overall survival (OS) was defined as the time from the initiation of mFOLFIRINOX to any cause of death. Results: Among 44 patients, 28 patients had ctDNA sequencing data qualified for the analysis and were included in this study (15 patients with baseline data only, 3 patients with post-operative data only, and 10 patients with both baseline and post-operative data). Median age was 59 (range, 41-73) years and 15 patients (53.6%) were male. Among 25 patients with baseline plasma ctDNA data, 11 patients (44%) had somatic or germline alteration of DDR genes detected at baseline including ATM, BRCA1, BRCA2 and MLH1, and showed significantly better PFS than those without such DDR gene alterations (median 26.6 vs. 13.5 months, log-rank p = 0.004). Although there was a trend for better OS in patients with DDR gene alterations, this was not statistically significant (log-rank p = 0.29). The most observed baseline somatic alteration was TP53 (n = 7, 28%), followed by KRAS (n = 6, 24%). Patients with somatic KRAS mutation at baseline had significantly worse OS (median 8.5 months vs. not applicable, log-rank p = 0.003) than those without. Among 13 patients with post-operative plasma ctDNA data, 8 patients (61.5%) had detectable somatic alterations. Conclusions: Detection of germline or somatic mutations of DDR genes from plasma ctDNA at baseline was associated with better survival outcomes of patients with borderline resectable PDAC treated with neoadjuvant mFOLFIRINOX. Detection of DDR gene alterations from plasma ctDNA may have a potential role as biomarker for prognosis in patients with borderline resectable PDAC treated with mFOLFIRINOX.

Abstract 1185: Survey of genomic alterations in Merkel cell carcinoma (MCC) in the AACR Project Genie real-world database

Abstract Introduction: MCC is a rare and highly aggressive cutaneous neuroendocrine carcinoma with increasing incidence over the last few decades. Cytotoxic chemotherapy and checkpoint inhibitors have provided modest treatment options, however, there are no approved or standard of care targeted treatment options. Here we surveyed the presence of targetable alterations in the AACR Project Genie Database Methods: Individual patient data were accessed from the cBioPortal. Variables of interest include demographic data, alterations annotated by OncoKB therapeutic evidence level, and TCGA PanCancer pathway alterations. Results: A total of 295 patients with MCC were cataloged in the database. Patients included were 34.6% (n=102) female with a median age of 71. Patients identified race as 91.2% (n=269) white, 2.4% (n=7) African American, and 0.4% (n=2) Asian. The median number of alterations was 3.00 (SD 21.4, Range 0-178). Oncogenic alterations represented 17.4% (n=660 of 3799) of mutations. Sampled tissue originated from primary tumor in 54% (n=161) verses metastases in 42.4% (n=125). NGS identified 18.5% (n=55) with an FDA approved drug for use in a biomarker approved indication or approved drug in another indication (Level 1-3). An additional 13.9% (n=41) had a Level 4 (L4) mutation. The most common Level 3B gene mutations include PIK3CA (4.1%, n=12), and BRCA1/2 (4.1%, n=12), HRAS (1.7%, n=5), TSC1/2 (1.7%, n=5). The most common L4 mutations include PTEN (4.4%, n=13), ARID1A (3.7%, n=11), and CDKN2A (2.4%, n=7). Only three fusions were identified; L3B fusions ATM-CDK12 and TSC2 along with Level 4 PTEN. Copy number alterations were identified in a small subset of patients. L3B CNAs include ATM, CHEK1 (n=1), BARD1 (n=1), BRCA2 (n=1), RAD51B (n=1), RAD51D (n=1). Level 4 CNAs identified CDKN2A (n=4) and PTEN (n=1). In 60.7% cases, PanCancer pathways were altered and 28.5% had alterations in multiple pathways. The most commonly altered pathways were RTK-RAS (37.6%, n=111), TP53 (33.9%, n=100), Cell Cycle (33.9, n=100), PI3K (32.2%, n=95) and NOTCH (30.8%, n=91). Additionally, oncogenic DNA damage repair gene alterations (BRCA1/2, CHEK1/2, ATM, PALB2, BRIP1, RAD51) were present in 7.5% (n=22) of cases. Conclusions: Here we identified a subset of patients with targetable mutations in MCC. The majority of patients had oncogenic alterations in cancer pathways which may support the investigation of kinase inhibitors as single agent or in combination with immunotherapy or cytotoxic chemotherapy in Merkel Cell Carcinoma. Citation Format: Danielle Brazel, Priyanka Kumar, Hung Doan, Justin T. Moyers. Survey of genomic alterations in Merkel cell carcinoma (MCC) in the AACR Project Genie real-world database [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1185.

The mutational pattern of DNA damage repair pathway in pancreatic cancer patients.

e16293 Background: Besides BRCA1/2, there are various genes involved in DNA damage repair that could predict patients’ response to treatments such as platin-based therapy, PARP inhibitors, and immunotherapy. While the mutational pattern of DNA damage repair (DDR) gene alterations in pancreatic patients remains unknown. Methods: Tumors and blood samples from 490 pancreatic patients were analyzed with next-generation sequencing (NGS) that covered 808 genes. Patients were classified based on the presence or absence of deleterious mutations across a panel of 98 DDR genes. Results: 70.4% (345/490) pancreatic cancer patients harbored DDR gene pathogenic mutations (mut). Among DDR-mut patients, 84.6% (292/345) had only somatic DDR gene alterations, 6.4% (22/345) had only germline DDR gene alterations, and 9.0% (31/345) had both. The most frequently mutated somatic DDR genes were TP53 (73.9%), CDKN2A (17.1%), ARID1A (10.1%), ATM (4.1%), and BRCA2 (4.1%). The most commonly mutated germline DDR genes were BRCA2 (4.1%), RAD51B (2.0%), ATM (2.0%), FANCE (0.9%), PALB2 (0.9%). Among the functional pathways of DDR genes, the most commonly mutated pathways were others (77.2%), FA (10.1%), CCC (7.7%), HR (1.5%), NHEJ (1.4%), MMR (1.4%), and BER (0.8%). No patients were found to harbor mutations in NER, TLS, and DR pathways. In addition, the mean TMB was significantly higher in the DDR-mut group compared with the wild-type DDR (wt) group (6.2 vs. 5.0 muts/Mb; p < 0.05). No significant difference in microsatellite instability was observed between DDR-mut and DDR-wt patients (p = 0.67). In terms of HRD status, 87.5% (28/32) HRD-positive patients and 73.1% (19/26) HRD-negative patients had DDR gene mutations. No significant difference in DDR variants was found between HRD-positive and HRD-negative patients, suggesting that HRD detection is necessary for DDR-mut patients. Within individual DDR genes, CDKN2A mutation was significantly associated with HRD-positivity (p < 0.05) whereas BRCA1, BRCA2, ATM, and PALB2 were not. Conclusions: An expanding set of DDR genes profiling provides more therapeutic opportunities for pancreatic patients who might benefit from PARP inhibitor owing to pathogenic mutations in DDR genes. This retrospective study may serve as a benchmark for the future design of an expanded association study between DDR mutations and the therapeutic outcome of pancreatic cancer.

Utilisation of semiconductor sequencing for the detection of predictive biomarkers in glioblastoma.

The standard treatment for glioblastoma involves a combination of surgery, radiation and chemotherapy but have limited impact on survival. The exponential increase in targeted agents directed at pivotal oncogenic pathways now provide new therapeutic opportunities for this tumour type. However, lack of comprehensive precision oncology testing at diagnosis means such therapeutic opportunities are potentially overlooked. To investigate the role of semiconductor sequencing for detection of predictive biomarkers in routine glioblastoma samples we have undertaken analysis of test trending data generated by a clinically validated next generation sequencing platform designed to capture actionable genomic variants distributed across 505 genes. Analysis was performed across a cohort of 55 glioblastoma patients. Analysis of trending data has revealed a complex and rich actionable mutational landscape in which 166 actionable mutations were detected across 36 genes linked to 17 off label targeted therapy protocols and 111 clinical trials. The majority of patients harboured three or more actionable mutations affecting key cancer related regulatory networks including the PI3K/AKT/MTOR and RAS/RAF/MEK/MAPK signalling pathways, DNA-damage repair pathways and cell cycle checkpoints. Linkage with immunotherapy and PARP inhibitors was identified in 44% of glioblastoma patients as a consequence of alterations in DNA-damage repair genes. Taken together our data indicates that precision oncology testing utilising semiconductor sequencing can be used to identify a broad therapeutic armamentarium of targeted therapies and immunotherapies that can be potentially employed for the improved clinical management of glioblastoma patients.

Genomic Profiling of Chinese Cervical Cancer Patients Reveals Prevalence of DNA Damage Repair Gene Alterations and Related Hypoxia Feature.

BackgroundCervical cancer is responsible for 10–15% of cancer-related deaths in women worldwide. In China, it is the most common cancer in the female genital tract. However, the genomic profiles of Chinese cervical cancer patients remain unclear.Materials and MethodsA total of 129 cervical cancer patients were enrolled in this study (113 squamous, 12 adenocarcinoma, 2 adenosquamous, and 2 neuroendocrine carcinoma). To classify the clinical features and molecular characteristics of cervical cancer, the genomic alterations of 618 selected genes were analyzed in the samples of these patients, utilizing target next-generation sequencing (NGS) technology. Furthermore, the findings from the Chinese cohort were then compared with the data of Western patients downloaded from The Cancer Genome Atlas (TCGA) database, in terms of gene expression files, mutation data, and clinical information.ResultsAll studied patients had valid somatic gene alterations, and the most frequently altered genes were PIK3C, TP53, FBXW7, ARID1A, ERBB2, and PTEN. Comparison of genomic profiling showed significantly different prevalence of genes, including TP53, KMT2C, and RET, between the Chinese and the TCGA cohorts. Moreover, 57 patients (44.19%) with 83 actionable alterations were identified in our cohort, especially in PI3K and DNA damage repair (DDR) pathways. After an in-depth analysis of cervical cancer data from the TCGA cohort, DDR alteration was found to be associated with extremely higher tumor mutation burden (TMB) (median mutation count: 149.5 vs 66, p <0.0001), and advanced stages (p <0.05). Additionally, DDR alteration, regardless of its function, was positively correlated with hypoxia feature and score. Moreover, patients with a high hypoxia score were positively correlated with a high abundance of mast cell resting, but lower abundance of CD8+ T cells and activated mast cell. Finally, CDHR5 was identified as the hub gene to be involved in the DDR–hypoxia network, which was negatively correlated with both the DDR alteration and hypoxia score.ConclusionsOverall, a unique genomic profiling of Chinese patients with cervical cancer was uncovered. Besides, the prevalent actionable variants, especially in PI3K and DDR pathways, would help promote the clinical management. Moreover, DDR alteration exerted the significant influence on the tumor microenvironment in cervical cancer, which could guide the clinical decisions for the treatment. CDHR5 was the first identified hub gene to be negatively correlated with DDR or hypoxia in cervical cancer, which had potential effects on the treatment of immune checkpoint inhibitors (ICIs).

Efficacy of neoadjuvant docetaxel + cisplatin chemo-hormonal therapy versus docetaxel chemo-hormonal therapy in patients with locally advanced prostate cancer with germline DNA damage repair gene alterations

Purpose:To assess the efficacy and safety of neoadjuvant docetaxel + cisplatin chemotherapy with androgen deprivation therapy for the treatment of locally advanced prostate cancer (PCa) in patients harboring germline DNA damage repair genes (gDDR) defects.Methods:We conducted a prospective observational study in patients with locally advanced PCa confirmed with gDDR defects through next-generation sequencing. All patients received either docetaxel + cisplatin (platinum-group) or docetaxel chemo-hormonal therapy (docetaxel group) followed by radical prostatectomy with extended lymphadenectomy. The primary end point was biochemical progression-free survival (bPFS) and secondary end points include postoperative pathological response and safety assessment during the study period.Results:A total of 36 patients were included in the study, among whom 14 and 22 patients received docetaxel + cisplatin and docetaxel treatment, respectively. Down-staging of Tumor (T), Nodes (N), and Metastasis (M) stages was observed in 11 (78.57%) and 9 (40.9%) patients (p = 0.041), respectively, in the docetaxel + cisplatin group and docetaxel group. The median bPFS was 7.76 months (95% CI 0.770–14.748) and not reached in the docetaxel group and docetaxel + cisplatin group, respectively. bPFS was significantly longer in the docetaxel + cisplatin group (p = 0.039) with a hazard ratio of 0.386 (95% CI 0.151–0.987, p < 0.05). Furthermore, one patient discontinued docetaxel + cisplatin after second cycle due to severe liver insufficiency which was confirmed as viral hepatitis A and no significant perioperative complications was observed in either group.Conclusion:This study suggests that cisplatin may increase docetaxel anticancer activity with tolerable safety profile in patients with locally advanced PCa carrying gDDR defects in the neoadjuvant setting, a hypothesis which will require prospective, randomized confirmation.

Targeting DNA damage repair pathways in pancreas cancer.

Pancreas ductal adenocarcinoma (PDAC) is the third most common cause of cancer death in the USA. While other cancers with historically poor prognoses have benefited from new immunotherapies and targeted agents, the 5-year survival rate for PDAC patients has remained static. The accessibility to genomic testing has improved in recent years, and it is now clear that PDAC is a heterogenous disease, with a subset of patients harboring actionable mutations. There are several targeted therapies approved by the Food and Drug administration (FDA) in PDAC: EGFR inhibitor erlotinib (combined with gemcitabine) in unselected patients, TRK inhibitors larotrectinib and entrectinib for patients with NTRK fusion mutation, the PD-1 inhibitor pembrolizumab for mismatch repair-deficient patients, and the poly-ADP-ribose polymerase (PARP) inhibitor olaparib in patients with germline BRCA mutation as a maintenance therapy. DNA damage repair (DDR) is paramount to genomic integrity and cell survival. The defective repair of DNA damage is one of the hallmarks of cancer, and abnormalities in DDR pathways are closely linked with the development of malignancies and upregulation of these pathways linked with resistance to treatment. The prevalence of somatic and germline mutations in DDR pathways in metastatic PDAC is reported to be approximately 15-25%. Patients with DDR gene alterations benefit from a personalized approach to treatment. Recently, the POLO trial demonstrated a progression-free survival (PFS) benefit in metastatic PDAC patients with a germline BRCA1/2 mutation treated with maintenance olaparib following platinum-based induction chemotherapy. This was the first phase 3 randomized trial to establish a biomarker-driven approach in the treatment of PDAC and establishes a precedent for maintenance therapy in PDAC. The review herein aims to outline the current treatment landscape for PDAC patients with DDR gene-mutated tumors, highlight novel therapeutic approaches focused on surmounting tumor resistance, and explore new strategies which may lead to an expansion in the number of patients who benefit from these targeted treatments.

Abstract 2040: Analysis of DNA damage repair gene alterations and their association with tumor mutation burden in 1427 hepatocellular carcinoma patients

Abstract Background: DNA damage repair (DDR) pathway have attracted much attention because they modulate cancer risk, progression and therapeutic response. DDR deficiency sensitize the tumor to poly ADP-ribose polymerase inhibitors (PARPi). Also alterations in DDR genes are associated with higher tumor mutation burden (TMB) and better response to immune checkpoint inhibitors (ICI). Here we conduct a large-scale genomic analysis to clarify the landscape of DDR gene mutations in hepatocellular carcinoma and the correlation between individual gene mutation and tumor mutation burden. Methods: Tumor samples from 1427 patients with advanced hepatocellular carcinoma were assayed through next-generation sequencing with 381 cancer-related genes including 30 predefined DDR genes: MRE11A, RAD50, BARD1, BLM, BRCA1, BRCA2, BRIP1, PALB2, MLH1, MSH2, MSH6, PMS2, POLD1, ATM, ATR, CHEK1, CHEK2, FANCA, FANCC, FANCD2, FANCG, FANCF, FANCL, RAD51, CUL3, ERCC1, POLE, MUTYH, and PRKDC. TMB (mutations per megabase [mut/Mb]) was calculated based on nonsilent somatic mutations in coding regions. Wilcoxon test was used for the comparisons and statistical significance was set at p = 0.05. Results: Somatic DDR gene alterations were found in 18.8% of the HCC patients. The most common mutational types were copy number variation (30.54%), frameshift (21.89%), and nonsense (20%). The most frequently altered DDR genes are ATM (2.6%) and BRCA2 (2.2%), followed by FANCA (0.9%), PALB2 (0.8%), and MLH1 (0.7%). As to different functional pathways of DDR, the gene alteration frequency from high to low is HRR (6.1%), DS (3.2%), FA (2.5%), MMR (2.2%), BER (0.6%), NHEJ (0.6%), and NER (0.3%). The TMB of patients carrying somatic DDR gene alterations was significantly higher than those without somatic DDR gene alterations (7.26 vs 6.45 mut/MB, p&amp;lt;0.001). As to individual gene, alterations in RAD50, MLH1, MSH2, CHEK2, and FANCE were significantly correlated with higher tumor mutation burden while alterations in other DDR genes were not. Conclusion: This is the largest study to clarify the landscape of DDR gene mutations in hepatocellular carcinoma. This study confirms that mutations in DDR genes are relatively common and are correlated with higher tumor mutation burden. This also indicates not all DDR genes are equal since mutations of certain individual genes were associated with higher TMB whereas others were not; further studies are needed to confirm this. Citation Format: Mengmei Yang, Wenzhuan Xie, Mengli Huang, Xinhua Zhu. Analysis of DNA damage repair gene alterations and their association with tumor mutation burden in 1427 hepatocellular carcinoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2040.

Abstract 2055: Evaluation of DNA damage repair gene alterations, microsatellite instability status, and tumor mutational burden as predictive biomarkers of olaparib sensitivity in gastric cancer

Abstract One of the many causes of cancer is a dysfunction of the DNA damage repair (DDR) pathway. Cancers with alterations in homologous recombination (HR) genes are known to be increased the sensitivity of PARP inhibitors and genomic instability. Besides, cancers with alterations in other DDR genes like mismatch repair (MMR), have been recently reported to have similar features. Furthermore, some studies suggested that hypermutated cancers, such as microsatellite instability-high (MSI-H) or tumor mutational burden (TMB) high, have DDR gene alterations. Nevertheless, many studies still have focused on HR-related gene alteration as a predictor of olaparib. Here, we aim to determine if the DDR gene alteration and genomic instability markers can predict olaparib efficacy in 49 gastric cancer cell lines. First, we profiled the genomic status of 48 DDR genes, MSI status, and TMB using targeted sequencing (524 genes). BRCA1, RAD51C, and MLH1 methylation were detected by bisulfite sequencing. If cell lines had the deleterious mutation, homozygous deletion, or methylation in DDR genes, it was categorized as an alteration group. To determine the efficacy of olaparib, cell lines were treated with olaparib for 5 days and assessed by CCK-8 assay. IC50 values were determined by the CalcuSyn software and cell lines were classified as a sensitive group when the IC50 was less than 10µM. MMR-related and PARP1 protein expression was determined by western blot. As a result, 17 cell lines had the alteration in one or more of the 18 DDR-related genes. In our cell line panel, the expression of PARP1 protein was varied, and 12 cell lines were sensitive to olaparib. DDR alteration group was more sensitive to olaparib than the DDR wild type group (median of IC50 = 14.08µM vs &amp;gt; 20µM, p = 0.034). In detail, cell lines with alterations in the HR and MMR were significantly sensitive among the subtype of DDR pathways (p = 0.011, p = 0.009). TMB was widely distributed among the GC cell lines (range = 4.36 to 21.80, median = 10.90), and the DDR alteration group had higher TMB than DDR wild type group (median = 11.63 vs 10.90, p = 0.029). Interestingly, the olaparib sensitive group had higher TMB than the resistant group (median = 15.3 vs 10.9, p &amp;lt; 0.0001). Four cell lines (SNU-1, SNU-638, IM95m, and NUGC-3) were MSI-H, and all of them were no MLH1 protein expression. MSI-H cell lines had significantly higher TMB than other cell lines (median=19.3, p &amp;lt; 0.0001). Three MSI-H cell lines were sensitive to olaparib, but NUGC-3 with the lowest TMB (13.8) among MSI-H cell lines was resistant. In our result, the olaparib sensitive group had the alteration in DDR genes and high TMB. MSI-H cell lines were sensitive to olaparib when it had high TMB. MSI status and TMB could predict olaparib sensitivity in gastric cancer as well as DDR gene alterations. Citation Format: Jihyun Hwang, Woo sun Kwon, Juin Park, Hyun Joo Bae, Inhye Jeong, Sun Kyoung Kang, Tae Soo Kim, Jingmin Che, Hyun Cheol Chung, Sun Young Rha. Evaluation of DNA damage repair gene alterations, microsatellite instability status, and tumor mutational burden as predictive biomarkers of olaparib sensitivity in gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2055.

Abstract 2050: Comprehensive genomic instability characteristics analysis in Chinese patients with osteosarcoma

Abstract Background: Previous study indicated that &amp;gt;80% of osteosarcomas (OSs) have genomic instability characteristics similar to BRCA1/2-deficient cancers. Such BRCA-like traits could manifest a deficiency in the DNA damage repair (DDR) pathway. Patients with alterations in DDR pathway was reported sensitive to platinum-based chemotherapy and PARP inhibitors. In order to seek more precision therapeutic opportunities, we explored the molecular profile of Chinese OS patients to identify whether the analogous phenomena exists as reported. Material and Methods: 44 archival Chinese OS patients from 3D Medicines and a public dataset including 35 OS patients (download from cBioPortal), were collected and analyzed next-generation sequencing (NGS) results on tumor tissues for gene mutations, copy number alterations (CNAs) and fusions in 33 cancer-associated DDR genes. Simultaneously, 44 Chinese OS patients' tumor analysis generated homologous recombination deficiency (HRD) scores (defined as the unweighted sum of LOH, TAI and LST scores) through the 733 gene panel sequencing. Results: Among 44 Chinese OS patients, 18 (40.9%) of OS had DDR pathway gene somatic alterations, and TP53 (31.8%) were the most frequently mapped gene. Other DDR somatic alterations were identified in BRCA2 (6.8%), BARD1 (4.5%), BRCA1 (2.3%), PMS2 (2.3%), FANCA (2.3%) and CHEK1 (2.3%). It was worth mention that all gene alterations were copy number reduction except TP53. Collectively, the frequencies of HRR and mismatch repair (MMR) alterations were 15.9% and 2.3%, respectively. HRD score were available in 18 patients, the median was 40.5 (range, 0-81). As to public dataset, 6 (17.1%) patients harbored somatic alterations in DDR genes. The variations were BRCA2 (5.7%), ATR (2.9%), BARD1 (2.9%), FANCC (2.9%), MLH1 (2.9%), MSH6 (2.9%) and PMS2 (2.9%). The HRR mutations frequency was 11% and MMR was 8.6%. Conclusions: This is the first large-scale comprehensive genomic instability characteristics analysis for Chinese patients with OS. Chinese patients and public dataset patients covers many common features. The DDR gene alteration frequency and HRD score are higher in OS patients, the association of variations in DDR genes and HRD score could be considered substitutable in predicting platinum-based therapy and PARP inhibitor response in clinical practice. Citation Format: Yonggang Wang, Hongtao Li, Jing Xia, Shiqing Chen, Yuezong Bai. Comprehensive genomic instability characteristics analysis in Chinese patients with osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2050.

Abstract 2206: Investigation of DNA damage repair mutated characteristics and correlation with immunogenic biomarker in Chinese head and neck cancer patients

Abstract Background: DNA damage repair (DDR) pathway have been reported in several cancer, and known as a predictive biomarker of platinum-based chemotherapy, PARP inhibitor therapy, radiotherapy, and immunotherapy. However, the predictive value and mutated characteristics of DDR in patients with head and neck cancer (HNC) is still uncertain. The purpose of this study is to assess the frequency of DDR mutations, and the correlation between DDR mutations and immunogenic biomarker such as tumor mutation burden (TMB), microsatellite instability (MSI) and PD-L1 expression in Chinese HNC patients. Methods: Genomic profiling of DNA was performed through a next-generation sequencing (NGS) (panel on 381/733-gene) on tissue from Chinese patients with head and neck cancer between January 23, 2017 and April 10 2020. TMB was defined as total number of somatic non-synonymous mutations in coding region. MSI was evaluated by NGS of 500 known MSI loci. PD-L1 expression was determined by immunohistochemistry staining using Dako 22C3. Germline or somatic mutations of 35 DDR genes were classified as DDR gene mutations. Result: Genetic mutation of 319 HNC patients were analyzed using NGS, of which 32 (10.03%) harbored alterations in DDR genes. The most frequently mutated DDR genes were BRCA2 (3.23%), followed by FANCA (2.02%), BRCA1 (1.61%), RAD51 (0.81%), RAD50 (0.81%), PMS2 (0.81%), and PLAB2 (0.81%). The frequency of KMT2C, CD274, FBXW7, APC, NOTCH1, PDCD1LG2, RB1, LRP1B, and JAK2 mutations was higher in DDR mutations (DDRmut) than in DDR wild-type (DDRwt) patients. PD-L1 status analysis was performed in 265 HNC patients, including 24 DDRmut patients and 241 DDRwt patients. But there was no significant difference on PD-L1 expression between DDRmut t and DDRwt (P=0.93). 310 HNC patients (including 31 DDRmut patients and 279 DDRwt patients) could be evaluated for TMB, the results showed that DDRmut (10.13Muts/Mb) was associated with higher TMB than DDRwt (5.65Muts/Mb) (P = 0.0031). Of the 308 HNC patients (including 31 DDRmut patients and 277 DDRwt), only 3 (0.97%) were diagnosed as MSI-H, including 2 (6.45%) patients with DDRmut and 1 (0.36%) patient with DDRwt. Conclusions: The DDR pathway genes alteration characteristics was presented in Chinese HNC patients, and was associated with a higher TMB level. These findings provide a theoretical basis for future investigation of clinical therapy in DDR mutated Chinese HNC patients. Citation Format: Yong Chen, Yan Wang, Yating Zheng, Wenzhuan Xie, Mengli Huang. Investigation of DNA damage repair mutated characteristics and correlation with immunogenic biomarker in Chinese head and neck cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2206.

Abstract 445: Genomic characteristics and response to rucaparib and enzalutamide in the phase 1b RAMP study of metastatic castration-resistant prostate cancer (mCRPC) patients

Abstract Background: Rucaparib, a poly(ADP-ribose) polymerase inhibitor (PARPi), is approved in the US as monotherapy for patients (pts) with BRCA1/2-mutated mCRPC after androgen receptor (AR)-directed therapy and a taxane. Synthetic lethality has been observed in studies combining AR-directed therapy (eg, enzalutamide) and a PARPi, independent of DNA-damage repair (DDR) gene defects. The RAMP study (NCT04179396) is investigating the safety and potential drug-drug interactions (DDIs) between rucaparib and enzalutamide in unselected mCRPC pts. In this exploratory analysis, we evaluated the association between treatment response and gene alterations of known clinical significance in mCRPC. Methods: Enrolled pts were previously treated with 0-2 lines of AR-directed therapy and ≤2 lines of chemotherapy for mCRPC. A 1-week run-in of rucaparib monotherapy (600 mg BID) was followed by rucaparib (600 mg BID) + enzalutamide (160 mg QD). Primary endpoints were pharmacokinetics (PK) and safety, including dose-limiting toxicities (DLTs). Change in prostate-specific antigen (PSA) levels from baseline was a secondary endpoint. As an exploratory objective, plasma and/or tissue samples were profiled for genomic alterations using a Foundation Medicine, Inc., assay to evaluate the relationship between genomics and clinical outcome. Results: As of Oct 1, 2020, 8 pts had received treatment; 7 were evaluable for PK and 6 for DLTs. The median age was 68.5 years and 7/8 (88%) pts had received 1 or 2 prior AR-directed therapies. The PK and overall safety profiles of rucaparib + enzalutamide were consistent with each as a single agent, and no DLTs were reported. Overall, 6/8 (75%) pts had a PSA decline, with 4/8 (50%) pts meeting criteria for a confirmed PSA response (≥50% decrease from baseline). Genomic data were available for 6/8 (75%) pts, all of whom had received prior AR-directed therapy. Of the 4/6 (66%) pts who had one or more somatic AR alterations, 3 had a PSA decline (best PSA change of -99%, -22%, and -17% from baseline) with the combination treatment. One pt had a DDR gene mutation, a subclonal (&amp;lt;1% allele frequency) alteration of CHEK2 with no PSA decline observed; no BRCA1/2 or PALB2 alterations were identified. Mutations in TP53 and PTEN were observed in 4/6 (67%) and 2/6 (33%) pts, respectively. Conclusions: A combination of enzalutamide and rucaparib had an acceptable safety profile and no clinically significant DDIs. In this small pt set, pts previously treated with AR-directed therapies showed responses to the combination even in the presence of AR alterations and in the absence of DDR gene alterations. These genomic and early efficacy data support further studies of rucaparib and enzalutamide at the recommended combination dose (rucaparib 600 mg BID + enzalutamide 160 mg QD), including in the phase 3 CASPAR study in biomarker-unselected mCRPC pts (NCT04455750). Citation Format: Arpit Rao, Charles J. Ryan, David Morris, Vasileios Assikis, Gautam Jha, Adriel-John Ablaza, Jenn Habeck, Andrea Loehr, Jim Xiao, Esha A. Gangolli. Genomic characteristics and response to rucaparib and enzalutamide in the phase 1b RAMP study of metastatic castration-resistant prostate cancer (mCRPC) patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 445.