3006 Background: Talazoparib, a PARP inhibitor, is active in germline BRCA1/2 mutant advanced HER2-negative breast cancer, but its activity beyond BRCA1/2 is unknown. We conducted a single institution phase II trial to evaluate talazoparib in patients (pts) with advanced HER2-negative breast cancer or other solid tumors with a germline (g) or somatic (s) alteration in HR pathway genes not including BRCA1/2. Methods: Eligible pts had measurable disease, lacked a germline or somatic mutation in BRCA1/2, received at least one prior therapy for advanced HER2-negative breast cancer or other solid tumor and had a HR pathway gene mutation: PALB2, CHEK2, ATM, NBN, BARD1, BRIP1, RAD50, RAD51C, RAD51D, MRE11, ATR, PTEN, FANCA, FANCC, FANCD2, FANCE, FANCF, FANCG, FANCL. Pts with no progression on or within 8 weeks of their last platinum dose were eligible. Pts were treated with talazoparib 1 mg po daily until disease progression. Response was assessed every 8 +/- 1 weeks. If 2 or more responses were observed in 10 pts in stage I, the study would proceed to stage II and enroll 10 additional pts. The null hypothesis of a ≤ 5% objective response rate would be rejected if at least 3 of 20 respond. Results: Twenty pts were enrolled; 13 breast cancer (12 HR+/HER2-, 1 TNBC) and 7 non-breast cancer (pancreas, colon, uterine, testicular, parotid salivary). Median age was 54 years. Of 12 response evaluable pts with breast cancer, 3 had a RECIST response (ORR = 25%, 2 g PALB2, 1 g CHEK2/g FANCA/sPTEN) and 3 additional pts (g PALB2, s ATR, s PTEN) had SD ≥ 6 months (CBR = 50%). No responses were seen in non-breast tumors; 2 (g CHEK2 testicular, g ATM colon) had SD ≥ 6 months. Talazoparib was well tolerated; 5 patients required dose reduction for hematologic toxicity. Results of tumor HR deficiency status assessment from metastatic biopsies and serial ctDNA profiling will be presented. Conclusions: In this proof-of-concept phase II study, single agent talazoparib demonstrated activity in HER2-negative advanced breast cancer pts with a HR pathway mutation beyond BRCA1/2. Further evaluation of talazoparib in this population is warranted. Clinical trial information: NCT02401347.

Talazoparib, a PARP inhibitor, is active in germline BRCA1 and BRCA2 (gBRCA1/2)-mutant advanced breast cancer, but its activity beyond gBRCA1/2 is poorly understood. We conducted Talazoparib Beyond BRCA (NCT02401347), an open-label phase II trial, to evaluate talazoparib in patients with pretreated advanced HER2-negative breast cancer (n = 13) or other solid tumors (n = 7) with mutations in homologous recombination (HR) pathway genes other than BRCA1 and BRCA2. In patients with breast cancer, four patients had a Response Evaluation Criteria in Solid Tumors (RECIST) partial response (overall response rate, 31%), and three additional patients had stable disease of ≥6 months (clinical benefit rate, 54%). All patients with germline mutations in PALB2(gPALB2; encoding partner and localizer of BRCA2) had treatment-associated tumor regression. Tumor or plasma circulating tumor DNA (ctDNA) HR deficiency (HRD) scores were correlated with treatment outcomes and were increased in all gPALB2 tumors. In addition, a gPALB2-associated mutational signature was associated with tumor response. Thus, talazoparib has been demonstrated to have efficacy in patients with advanced breast cancer who have gPALB2 mutations, showing activity in the context of HR pathway gene mutations beyond gBRCA1/2.

PURPOSE: To understand genetic testing use and decision making among patients with high genetic risk. MATERIALS AND METHODS: A survey of breast cancer survivors was administered online by a hereditary cancer nonprofit organization, Facing Our Risk of Cancer Empowered, from October 2017 to March 2018. RESULTS: Of 1,322 respondents, 46% had breast cancer at age < 45 years, 61% had a first-degree relative with cancer, and 84% underwent genetic testing, of whom 56% had a risk-associated pathogenic variant. Most (86%; 95% CI, 84% to 88%) tested respondents were very satisfied with their testing decision, versus 34% (95% CI, 27% to 41%) of untested respondents. Factors that encouraged testing included relatives’ cancer risk (75%; 95% CI, 73% to 78%), clinicians’ recommendations (68%; 95% CI, 66% to 71%), and potential treatment implications (67%; 95% CI, 64% to 69%). Factors that discouraged testing included insurance concerns (14%; 95% CI, 12% to 16%), cost (14%; 95% CI, 12% to 16%), and discrimination (9%; 95% CI, 7% to 11%). Thirty-nine percent (95% CI, 36% to 41%) recalled hearing from a clinician that genetic discrimination is illegal. Respondents often recalled clinicians informing them about inheritance patterns (65%; 95% CI, 62% to 67%), surgical implications (65%; 95% CI, 63% to 68%), and other cancer risks (66%; 95% CI, 63% to 68%) but less often that results could have potential implications for clinical trial eligibility (38%; 95% CI, 36% to 42%) or targeted therapies (14%; 95% CI, 12% to 16%). Patients who had genetic counseling were twice as likely to recall clinicians informing them about all queried topics. Results did not vary by diagnosis year. CONCLUSION: Among patients with high genetic risk, clinicians’ recommendations, potential treatment implications, and protections against discrimination were motivating factors to undergo genetic testing, but fewer than half recalled clinicians providing all this information, and this did not improve over time. Clinicians influence testing decisions and should inform patients about legal protections and treatment implications.

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