Berchuck, Jacob E.

27 Background: Validated homozygous loss detection is becoming increasingly important in clinical practice, with prostate NCCN guideline inclusion of BRCA1/2 loss (often portending durable PARP inhibitor benefit) and multi-tumor trials of PRMT5 and MAT2A inhibitors ongoing (biomarker: MTAP loss). Homozygous losses are challenging to detect and require intentional NGS assay design and validations. Using an FDA-approved NGS assay, we evaluated the most frequent losses identified in metastatic prostate cancer, evaluated prognostic associations on ARPI, and prevalence before and after ARPI treatments. Methods: This study used the nationwide (US-based) de-identified Flatiron Health-Foundation Medicine Prostate Cancer clinico-genomic database (FH-FMI CGDB), originating from approximately 280 US cancer clinics (~800 sites of care). Patients with metastatic prostate cancer and tissue tumor genomic testing by FoundationOne CDx were eligible for analysis. Alteration prevalence was compared between non-sequential groups of specimens obtained from patients naïve to ADT and ARPI, naïve to ARPI but not ADT, or exposed to any ARPI. Outcome analyses adjusted for: ECOG performance score, age, baseline PSA, and socioeconomic status. To limit immortal time confounding, outcome analyses were restricted to patients with specimens tested prior to initiation of ARPI. Results: 1990 specimens from 1984 unique patients met criteria for assessment. The most common losses and respective ADT & ARPI naïve vs ADT exposed & ARPI-naïve vs ARPI-exposed prevalence were PTEN (17.1% vs 24.8% vs. 33.5%, p < 0.001), FAS (2.4% vs 5.0% vs 5.8%, p = 0.003), BRCA2 (4.2% vs 3.2% vs. 2.8%, p = 0.36), RB1 (1.6% vs 3.0% vs 3.5%, p = 0.062), and TP53 (2.3% vs 2.3% vs 4.4%, p = 0.064). 227 patients had tissue specimens obtained and NGS results reported prior to initiation of ARPI. Sufficient patients with PTEN loss were present for nominal outcome associations, observing less favorable time to next treatment (HR: 1.81, 95%CI: 1.24 – 2.65, p = 0.002) and overall survival (HR: 1.65, 95%CI: 1.02 – 2.65, p = 0.040) from the initiation of ARPI. In the mHSPC (ADT and ARPI naïve) setting, 17.1% had PTEN loss, 32.8% had an HRR gene alteration, and 2.8% had both. Conclusions: Our results are consistent with homozygous losses of certain genes, notably PTEN , potentially being acquired resistance alterations to ARPI. Prostate cancer trials often do not specify timing of specimen acquisition relative to treatment initiation. For trials like IPATential-150 or CAPItello-280 that evaluate AKT inhibitors in post-ARPI setting, patients with PTEN status determined by archival tissue could be false negatives and reduce power of analysis in biomarker(+) group. Our results underscore the importance of clinical context, especially prior treatment exposures, when interpreting biomarker prevalence.

AbstractBackgroundPARP (poly(ADP‐ribose) polymerase) inhibitors (PARPi) are now standard of care in metastatic castrate‐resistant prostate cancer (mCRPC) patients with select mutations in DNA damage repair (DDR) pathways, but patients with ATM‐ and BRCA2 mutations may respond differently to PARPi. We hypothesized that differences may also exist in response to taxanes, which may inform treatment sequencing decisions.MethodsmCRPC patients (N = 158) with deleterious ATM or BRCA2 mutations who received taxanes, PARPi, or both were retrospectively identified from 11 US academic centers. Demographic, treatment, and survival data were collected. Kaplan−Meier analyses were performed and Cox hazard ratios (HR) were calculated for progression‐free survival (PFS) as well as overall survival (OS), from time of first taxane or PARPi therapy.ResultsFifty‐eight patients with ATM mutations and 100 with BRCA2 mutations were identified. Fourty‐four (76%) patients with ATM mutations received taxane only or taxane before PARPi, while 14 (24%) received PARPi only or PARPi before taxane. Patients with ATM mutations had longer PFS when taxane was given first versus PARPi given first (HR: 0.74 [95% confidence interval [CI]: 0.37−1.50]; p = 0.40). Similarly, OS was longer in patients with ATM mutations who received taxane first (HR: 0.56 [CI: 0.20−1.54]; p = 0.26). Among patients with BRCA2 mutations, 51 (51%) received taxane first and 49 (49%) received PARPi first. In contrast, patients with BRCA2 mutations had longer PFS when PARPi was given first versus taxane given first (HR: 0.85 [CI: 0.54−1.35]; p = 0.49). Similarly, OS was longer in patients with BRCA2 mutations who received PARPi first (HR: 0.75 [CI: 0.41−1.37]; p = 0.35).ConclusionsOur retrospective data suggest differential response between ATM and BRCA2 mutated prostate cancers in terms of response to PARPi and to taxane chemotherapy. When considering the sequence of PARPi versus taxane chemotherapy for mCRPC with DDR mutations, ATM, and BRCA2 mutation status may be helpful in guiding choice of initial therapy.

PURPOSE Two poly (ADP-ribose) polymerase (PARP) inhibitors (olaparib and rucaparib) are US Food and Drug Administration–approved for patients with metastatic castration-resistant prostate cancer (mCRPC) harboring BRCA1/ 2 mutations, but the relative efficacy of PARP inhibition in BRCA1- versus BRCA2-altered mCRPC is understudied. METHODS We conducted a multicenter retrospective analysis involving 12 sites. We collected genomic and clinical data from 123 patients with BRCA1/ 2-altered mCRPC who were treated with PARP inhibitors. The primary efficacy end point was the prostate-specific antigen (PSA) response (≥ 50% PSA decline) rate. Secondary end points were PSA progression-free survival (PSA-PFS), clinical or radiographic PFS, and overall survival. We compared clinical outcomes, and other genomic characteristics, among BRCA1- versus BRCA2-altered mCRPC. RESULTS A total of 123 patients (13 BRCA1 and 110 BRCA2) were included. PARP inhibitors used were olaparib (n = 116), rucaparib (n = 3), talazoparib (n = 2), and veliparib (n = 2). At diagnosis, 72% of patients had Gleason 8-10 disease. BRCA1 patients were more likely to have metastatic disease at presentation (69% v 37%; P = .04). Age, baseline PSA, metastatic distribution, and types of previous systemic therapies were similar between groups. There were equal proportions of germline mutations (51% v 46%; P = .78) in both groups. BRCA1 patients had more monoallelic (56% v 41%; P = .49) and concurrent TP53 (55% v 36%; P = .32) mutations. PSA 50 responses in BRCA1- versus BRCA2-altered patients were 23% versus 63%, respectively ( P = .01). BRCA2 patients achieved longer PSA-PFS (HR, 1.94; 95% CI, 0.92 to 4.09; P = .08), PFS (HR, 2.08; 95% CI, 0.99 to 4.40; P = .05), and overall survival (HR, 3.01; 95% CI, 1.32 to 6.83; P = .008). Biallelic (compared with monoallelic) mutations, truncating (compared with missense) mutations, and absence of a concurrent TP53 mutation were associated with PARP inhibitor sensitivity. CONCLUSION PARP inhibitor efficacy is diminished in BRCA1- versus BRCA2-altered mCRPC. This is not due to an imbalance in germline mutations but might be related to more monoallelic mutations and/or concurrent TP53 alterations in the BRCA1 group.

5040 Background: PARPi have shown promise in mCRPC pts with mutations in DNA repair, but ATM- and BRCA2-altered pts may respond differently to PARPi. We hypothesized that differences may also exist for taxane therapy, aiding in treatment sequencing decisions. Methods: mCRPC pts (N = 137) with deleterious ATM or BRCA2 mutations who received taxanes, PARPi, or both were identified from 8 US academic centers. Demographic, treatment, and survival data were collected. Kaplan-Meier analyses were performed for time-to-treatment-discontinuation (TTD), as well as overall survival (OS), from time of first taxane or PARPi therapy. Cox hazard ratio (HR) regression analyses were performed, adjusting for Gleason sum (≤7 vs. 8-10). For OS, receipt of subsequent therapies following first taxane or PARPi was also included as a covariate. Results: 50 ATM- and 87 BRCA2-mutated pts were identified. 40/50 (80%) of ATM-mutated pts received taxane only or taxane prior to PARPi, while 10/50 (20%) received PARPi only or PARPi prior to taxane. ATM-mutated pts showed a trend towards longer TTD when taxane was given first vs PARPi given first (P = 0.08, adjusted HR for taxane treatment 0.50 [95% CI: 0.24–1.08]). Considering all pts who received taxane first, ATM-mutated pts had longer TTD than BRCA2-mutated pts who received taxane first ( P= 0.04, adjusted HR for ATM 0.61 [CI: 0.37–0.99]). Among ATM-mutated pts, OS was longer in those receiving taxane first ( P= 0.06, adjusted HR for taxane treatment 0.33 [CI: 0.10–1.05]). Among BRCA2-mutated pts, 43/87 (49%) received taxane first and 44/87 (51%) received PARPi first. BRCA2-mutated pts had longer TTD when PARPi was given first vs taxane given first ( P< 0.0001, adjusted HR for PARPi treatment 0.32 [CI: 0.19–0.56]). Considering all pts who received PARPi first, BRCA2-mutated pts also had longer TTD than ATM-mutated pts who received PARPi first ( P= 0.0031, adjusted HR for BRCA2 0.29 [CI: 0.12–0.66]). There was no significant OS difference in BRCA2-mutated pts regarding which treatment was given first ( P= 0.63, adjusted HR for PARPi treatment 1.18 [CI: 0.59–2.35]). Conclusions: Our data in ATM- and BRCA2-mutated mCRPC pts suggests a trend towards improved clinical outcomes when taxanes are used prior to PARPi in ATM-mutated pts, while the reverse sequence appears to be better for BRCA2-mutated pts.[Table: see text]

100 Background: Two PARP inhibitors (olaparib, rucaparib) are now FDA approved for mCRPC patients with mutations in BRCA1/2, but the relative efficacy of PARP inhibition in BRCA1- vs BRCA2-altered mCRPC is understudied. Methods: We conducted a multi-center retrospective analysis involving 11 academic sites. We collected genomic and clinical data from 123 BRCA1/2-altered mCRPC patients receiving PARP inhibitor treatment. The primary efficacy endpoint was PSA50 response rate (≥50% decline in PSA level). Secondary endpoints were PFS (clinical, radiographic or PSA progression, whichever occurred first) and overall survival (OS). We also captured information on other concurrent genomic alterations. We compared genomic characteristics and clinical outcomes among BRCA1- vs BRCA2-altered mCRPC. Results: A total of 123 patients (13 BRCA1, 110 BRCA2) were included. PARP inhibitors used were olaparib (n = 116), rucaparib (n = 3), talazoparib (n = 2) and veliparib (n = 2). All BRCA1 and 71% of BRCA2 patients had Gleason 8-10 disease. Compared to BRCA2 patients, BRCA1 patients were more likely to have received prior taxane chemotherapy (77% vs 62%). Age, baseline PSA, and prior enzalutamide/abiraterone treatment were similar between groups. PSA50 responses in BRCA1- vs BRCA2-altered patients were 38% vs 65% respectively ( P= 0.06). Median PFS in BRCA1 vs BRCA2 patients was 3.0 mo (95%CI, 0.9–5.1) vs 8.0 mo (95%CI, 5.3–10.6) respectively (HR 0.42, P= 0.01). Similarly, median OS in BRCA1 vs BRCA2 patients was 11.0 mo (95%CI, 9.9–12.1) vs 24.0 mo (95%CI, 18.2–29.8) respectively (HR 0.33, P= 0.005). There were roughly equal proportions of germline mutations (50% vs 45%) and biallelic mutations (31% vs 25%) in the BRCA2 and BRCA1 groups, respectively. There were numerically more TP53 mutations in the BRCA1 vs BRCA2 group (40% vs 29%, P= 0.45), but an equal number of mutations in other key genes ( PTEN, RB1 and AR). Conclusions: PARP inhibitor activity is diminished in BRCA1- vs BRCA2-altered mCRPC. In our cohort, this differential activity was not explained by mutation origin (germline vs somatic) or allelic status (mono- vs biallelic). These findings warrant validation.