Abstract P5-13-36: Germline <i>BRCA</i>1/2 and other predisposition genes in high-risk early-stage HR+/HER2- breast cancer (BC) patients treated with endocrine therapy (ET) with or without palbociclib: A secondary analysis from the PENELOPE-B study

Abstract Background: In high-risk hormone-receptor (HR)+/HER2- BC patients germline (g) mutations can be found in approximately 14% in BRCA1/2 and in BRCA1/2 and other BC predisposition genes in 20% (Pohl-Rescigno E, et al. JAMA Oncol 2020). In metastatic BC CDK4/6 inhibitors may have greater activity in patients with a BRCA mutation detected in ctDNA (André F, et al. J Clin Oncol 2020). The PENELOPE-B trial did not to show an improved invasive disease-free survival (iDFS) by adding palbociclib to ET in high-risk HR+/HER2- BC (Loibl S, et al. J Clin Oncol 2021). Methods: Blood samples from 898 of 1250 PENELOPE-B patients were available. 445 patients were sampled following a case-cohort design (220 cases defined as patients with any event during follow-up and 225 randomly selected patients without any event [non-cases]) and analyzed for germline variants in BRCA1/2 and 16 non-BRCA1/2 cancer predisposition genes (ATM, BARD1, BRIP1, CDH1, CHEK2, FANCM, MRE11A, NBN, PALB2, PTEN, RAD50, RAD51C, RAD51D, STK11, TP53, XRCC2) by targeted next generation sequencing (NGS). The primary definition of mutational status was the prevalence of a pathogenic mutation (mt) in one or more analyzed BC predisposition genes. Statistical analyses for time-to-event endpoints (iDFS, distant disease-free survival [DDFS], and overall survival [OS]) were based on inverse probability weighting: weighted Cox proportional hazard models and Kaplan-Meier estimates were used. Results: 442 of 445 patients (placebo arm: 104 cases and 105 non-cases; palbociclib arm: 114 cases and 119 non-cases) were successfully analyzed for mutational status. A total of 42 (9.5%) patients (placebo arm: 9.1%; palbociclib arm: 9.9%) carried any mutation. 15 (3.4%) patients had a gBRCA1/2 mt (one of whom carried a gATM mt and one a gCHEK2 mt in addition to gBRCA2 mt) and 29 (6.6%) had mutations in one of the other BC predisposition genes (n=8 CHEK2, n=7 PALB2, n=5 ATM, n=2 RAD50, n=1 for BARD1, FANCM, MRE11A, RAD51C, RAD51D, TP53 and n=1 both RAD51D and BRIP1). The mutational status with respect to all genes analyzed showed no significant correlation to clinical baseline variables. With regard to gBRCA1 and gBRCA2 genes only, the mutational status significantly correlated with age but not with other clinical variables: all 15 (100%) gBRCA mt carriers were younger than 50 years compared to 238 (56%) wildtype (wt) patients (p=0.002). The iDFS rate after 3 years was 80.9% in patients with any mutation and 79.5% in patients without. Mutational status (mt vs. wt) based on all genes analyzed was not prognostic (iDFS: hazard ratio 1.015, 95%CI 0.558-1.784; DDFS: 0.970, 95%CI 0.521-1.758; OS: 0.768, 95%CI 0.274-1.615). Neither the mutated patients had a benefit from palbociclib treatment (palbociclib vs placebo; iDFS: hazard ratio 0.766, 95%CI 0.263-3.022; DDFS: 0.897, 95%CI 0.275-3.489; OS: 0.666, 95%CI 0.063-5.671) nor the wt patients (iDFS: hazard ratio 0.918, 95%CI 0.650-1.303; DDFS: 0.966, 95%CI 0.679-1.393; OS: 0.901, 95%CI 0.573-1.433); interaction tests for treatment arm/mutational status for all time-to-event endpoints were not statistically significant. Analysis in the subgroups of patients by gBRCA1/2 showed similar results but had less statistical power. Conclusions: In this case-cohort analysis of 442 patients enrolled in the PENELOPE-B trial, the detection of BC predisposition genes was lower than expected with 10%. This is probably due to the low rate of gBRCA1/2 carriers (3.4%), which could be influenced by the selection criteria of the trial. Patients with gBRCA1/2 or other BC disposition genes had a comparable outcome to non-carriers in the PENELOPE-B trial. Citation Format: Sibylle Loibl, Jan Hauke, Karen Gelmon, Frederik Marmé, Corinna Ernst, Miguel Martin, Michael Untch, Hervé Bonnefoi, Erik Knudsen, Seock-Ah Im, Angela DeMichele, Laura Van’t Veer, Sung-Bae Kim, Harry Bear, Nicole McCarthy, Nicholas Turner, Agnieszka Witkiewicz, Federico Rojo, Peter A Fasching, José A García-Sáenz, Catherine M Kelly, Toralf Reimer, Masakazu Toi, Hope S Rugo, Carsten Denkert, Michael Gnant, Andreas Makris, Yuan Liu, Olga Valota, Bärbel Felder, Karsten Weber, Valentina Nekljudova, Eric Hahnen. Germline BRCA1/2 and other predisposition genes in high-risk early-stage HR+/HER2- breast cancer (BC) patients treated with endocrine therapy (ET) with or without palbociclib: A secondary analysis from the PENELOPE-B study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-36.

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