Abstract PS5-07: A retrospective analysis of association of MYC and RAD21 amplification with final overall survival (OS) data in the phase 3 EMBRACA study with talazoparib

Abstract

Abstract Background: Loss-of-function mutations in genes encoding components of the homologous recombination DNA damage response (DDR) machinery, notably BRCA1/2, are associated with tumor sensitivity to poly(ADP-ribose) polymerase inhibitors (PARPi). Little is known about the potential contribution of tumor alterations in non-DDR genes to modulating sensitivity to PARP inhibitors in the clinic. In EMBRACA, the PARPi TALA improved progression-free survival (PFS) (HR [95% CI] 0.54 [0.41-0.71], P<0.001) vs chemotherapy (CT) in germline BRCA1/2-mutated HER2-negative locally advanced/metastatic breast cancer. Methods: Baseline tumor tissue from 308 pts (71%; intent-to-treat) was tested by FoundationOne®. To support exploratory identification of tumor gene alterations associated with best vs worst outcomes, pts were mapped into 2 groups: [1] BEST: Pts in TALA arm with OS ≥ 30 mo and duration of treatment ≥ 24 mo, Pts in CT arm with OS ≥ 30 mo; [2] WORST: Pts in TALA or CT arm with a PFS event (PD by Independent Radiological Facility or death) ≤ 12 wks. 2 pts had short PFS but long OS and were initially mapped to both groups but then assigned to BEST and excluded from WORST. Results: Exploratory heat map visualizations of known/likely pathogenic genetic alterations defined by the FoundationOne® gene panel were used to assess differences in genetic alterations between BEST and WORST in TNBC and non-TNBC subpopulations, leading to the identification of MYC and RAD21 as commonly altered genes of high interest. Based on these results showing imbalances in tumor amplification events between BEST and WORST outcome pts, Cox regression analysis was used to explore potential associations of MYC or RAD21 amplification with OS across the evaluable ITT population. In TNBC pts receiving TALA, OS was shorter with MYC amplification than without [HR (95% CI) 1.877 (1.102, 3.196)]. No such association was evident in TNBC pts receiving CT [HR (95% CI) 0.706 (0.303, 1.643)]. In contrast, for non-TNBC pts receiving TALA, no association with OS was evident for MYC amplification versus without [HR (95% CI) 0.603 (0.310, 1.173)], while for pts receiving CT OS was shorter with MYC amplification than without [HR (95% CI) 1.917 (1.037, 3.544)]. RAD21 amplification status was not associated with OS in either TNBC or non-TNBC patients for either treatment arm, although it should be noted that two RAD21 subgroups were very small (n=7 and 11; others had n ≥ 21). Conclusions: Based on these exploratory, retrospective analyses MYC amplification was associated with shorter OS in TNBC pts receiving TALA. This may reflect the role of MYC in positive regulation of genes involved in homologous recombination such as RAD51 (Carey et al, Cancer Res 2018;78(3):742-757). MYC and RAD21 are both located at 8q24 and frequently coamplified in breast cancer (eg, Annunziato et al, Nat Commun. 2019;10(1):397), hence the lack of association of RAD21 amplification with outcome in TNBC suggests that the association of MYC amplification with shorter OS seen in pts receiving TALA may be gene-specific. Further investigation is warranted. Funding: Pfizer TNBCNon-TNBCTALACTTALACTGene AlterationBest n=10Worst n=15Best n=7Worst n=16Best n=17Worst n=11Best n=20Worst n=11MYC amplification0 (0%)7 (47%)2 (29%)6 (38%)5 (29%)1 (9%)3 (15%)5 (46%)RAD21 amplification1 (10%)2 (13%)3 (43%)5 (31%)5 (29%)1 (9%)7 (35%)4 (36%) Citation Format: Johannes Ettl, A. Douglas Laird, Joanne L. Blum, Hope S. Rugo, Sara A. Hurvitz, Miguel Martín, Henri Roché, Young-Hyuck Im, Annabel Goodwin, Rinat Yerushalmi, Tiziana Usari, Silvana Lanzalone, Akos Czibere, Julia Hopkins, Lee A. Albacker, Lida A. Mina, Jennifer K. Litton. A retrospective analysis of association of MYC and RAD21 amplification with final overall survival (OS) data in the phase 3 EMBRACA study with talazoparib [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 PS5-07.