Abstract A037: Differences in BRCAness/PARP inhibitor response signatures and homologous recombination gene expression across lung adenocarcinoma and squamous cell carcinoma gene expression subtypes

Background: Gene expression-based subtyping in lung adenocarcinoma (AD) and lung squamous cell carcinoma (SQ) classifies AD and SQ tumors into distinct subtypes with variable expression of underlying biology including DNA damage response genes. These subtypes are linked to differences in chemotherapy sensitivity, and may impact response to therapeutics like PARP inhibitors. Methods: Using The Cancer Genome Atlas (TCGA) lung cancer gene expression datasets (AD n=515 and SQ n=501), AD subtypes (Terminal Respiratory Unit (TRU), Proximal Proliferative (PP), and Proximal Inflammatory (PI)) and SQ subtypes (Primitive, Classical, Secretory, and Basal) were defined using gene expression based centroid predictors. Association between AD and SQ expression subtypes and 3 published BRCAness/PARP inhibitor response signatures developed in ovarian and/or breast cancer (Konstantinopoulos et al., PMID 20547991; Daemen et al., PMID 22875744; McGrail et al., PMID 28649435) was examined using linear regression. Association between subtypes and expression of 15 recognized homologous recombination (HR) related genes (ATM, ATR, BRCA1, BRCA2, BRIP1, CDK12, CHEK1, CHEK2, FANCA, FANCI, FANCD2, MRE11A, RAD51C, RAD51L1, PTEN) was also examined using linear regression, and association tests included adjustment for the 3 BRCAness/PARP inhibitor response signatures and proliferation score. Results: AD and SQ subtypes showed strong association with the 3 BRCAness/PARP inhibitor response signatures (F-test p-values 7.7e-05, 5.9e-13, 9.4e-33 in AD and 1.9e-05, 9.0e-13, 2.7e-19 in SQ). AD and SQ subtypes showed strong association with 15 HR genes (max and median F-test p-values were 8.5e-04 and 7.5e-25 in AD, and 7.3e-04 and 1.4e-12 in SQ). The TRU subtype in AD showed low expression relative to the other AD subtypes for a majority of the HR genes, including BRCA1. In SQ, the same was true for the basal and secretory subtypes. Simultaneous adjustment for the 3 BRCAness/PARP inhibitor response signatures, as well as for proliferation, reduced association strength between subtype and HR gene expression in AD and less so in SQ. In AD, association between subtype and gene expression remained significant for 4 HR genes (using Bonferroni correction for 15 tests), including CHECK2, FANCI, BRIP1, and RAD51L1. In SQ, association between subtype and gene expression remained significant for all HR genes except CHEK1 and FANCA, (median and min Bonferroni-adjusted p-value 2.9e-04 and 2.6e-21). Conclusions: Intrinsic biologic subtypes of lung AD and SQ are associated with published BRCAness/PARP inhibitor response signatures and reveal differential expression of several HR-related genes. Evaluation of these subtypes, particularly in SQ, as potential biomarkers of PARP inhibitor sensitivity should be investigated. Citation Format: Gregory Mayhew, Chuck Perou, D Neil Hayes, Myla Lai-Goldman, Hawazin Faruki. Differences in BRCAness/PARP inhibitor response signatures and homologous recombination gene expression across lung adenocarcinoma and squamous cell carcinoma gene expression subtypes [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A037.