Abstract PS10-36: Treatment patterns and clinical outcomes among patients (pts) with HER2- advanced breast cancer (ABC) and somatic BRCA1/2 mutation(s) (sBRCA1/2mut): Results from a US real-world study
Authors: Obeid Elias , Parikh Rohan C , Esterberg Elizabeth , Arondekar Bhakti , Hitchens Abigail , Arruda Lillian Shahied , Niyazov Alexander 
Published: February 2021

Background: Recently, somatic genetic information is being increasingly usedin clinical decisions for treatment of metastatic diseases, including breastcancer. Somatic mutations in the BRCA1/2 genes are not frequently seen.The poly ADP-ribose polymerases inhibitors (PARPi) have been approved astreatments for patients with germline (gBRCA1/2mut) HER2- ABC. Real-world practice shows that these agents arealso being utilized for patients who have sBRCA1/2mut. While we await data from large clinicaltrials such as MATVH and TAPUR, currently, limited information is available onthe effectiveness of these agents in patients with sBRCA1/2mut andestablishing a reference point is necessary to assess the unknown potentialclinical benefit. We assessed real-world treatment patterns and clinicaloutcomes among patients with HER2- sBRCA1/2mut without associatedgermline mutation and who had received treatment for ABC. Methods: US oncologists retrospectivelyreviewed charts (July 2019-June 2020) of quasi-randomly selected patients ≥18y, who received ≥1 cytotoxic chemotherapy (CT) regimen(s) for ABC between Jan2013-April 2018. Descriptive analyses were performed for patients with sBRCA1/2mut(without associated germline mutation), which included evaluation of treatment patternsand safety events for the first 3 lines of therapy. Clinical outcomes(progression free survival [PFS] and overall survival rates) were estimatedusing the Kaplan-Meier method for 1st line of therapy. Given therelatively recent launch of PARPi, clinical outcomes for these agents wereimmature. Results: 32 patients were included who only had sBRCA1/2mut: 96.9%were female, 68.8% were white, and 28.1% were black. Median age was 53.0 yrs. Advanced triplenegative breast cancer was observed in 40.6% of patients and 59.4% had hormonereceptor (HR)+/HER2- ABC. Common treatments for HR+/HER2- sBRCA1/2mutdisease included: 1st line (n=19), cyclophosphamide + doxorubicin (10.5%);2nd line (n=17), docetaxel (11.8%), PARPi monotherapy (11.8%), CDK4/6i + letrozole (11.8%); 3rd line- (n=7), eribulin (42.9%). Treatments for triplenegative sBRCA1/2mut breast cancer included: 1st line (n=13), cyclophosphamide + doxorubicin (30.8%);2nd line (n=9), PARPi (22.2%); 3rd line (n=7),atezolizumab based (71.4%). Median PFS across both subtypes was 10.8 months,95% CI 8.5 - 15.0. Overall, 78.9% of patients were alive at 2 years after 1stCT. Safety data will be presented. Conclusion: In this analysis of sBRCA1/2mut HER2- ABC, an individualapproach to select treatment regimens such as CT was frequently used, withoutadequate knowledge on best sequential therapy to include tumor genetic directedintervention. Poor clinical outcomes highlight the need for more efficacioustreatment options. Further studies assessingclinical outcomes among patients with sBRCA1/2mut ABC receivingPARPi are warranted.

Citation Format: Elias Obeid, Rohan C Parikh, Elizabeth Esterberg, Bhakti Arondekar, Abigail Hitchens, Lillian Shahied Arruda, Alexander Niyazov. Treatment patterns and clinical outcomes among patients (pts) with HER2- advanced breast cancer (ABC) and somatic BRCA1/2 mutation(s) (sBRCA1/2mut): Results from a US real-world study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-36.