Exploring the nuances between BRCA1 and 2: A multiomic analysis.
Authors: Gogoi Radhika , Wu Sharon , Farrell Alex , Kim Seongho , Wallbillich John , Winer Ira Seth , Morris Robert , Spetzler David , Puccini Alberto , Jones Nathaniel L. , Herzog Thomas J. , Thaker Premal H. , Mor Gil , Alvero Ayesha 
Published: June 2022

5580 Background: Emerging data suggests that key differences exist between BRCA1 and BRCA2 associated OC, including response to therapy and survival. The purpose of this study was to identify the gene expression profiles, interacting pathways and immune microenvironment of BRCA1 mutant (BRCA1mut), BRCA2 mutant (BRCA2mut) and homologous recombination wild-type (HRwt) associated high grade serous OC (HGSOC). Methods: Next-generation sequencing (592, NextSeq; WES, NovaSeq) and Whole Transcriptome Sequencing (NovaSeq) (Caris Life Sciences, Phoenix, AZ) were performed in 8196 OC tumors classified into 3 groups: BRCA1mt; BRCA2mt; and HRwt. BRCA mutations were defined as variants that result in loss-of-function of the BRCA protein and HRwt was defined as samples negative for aberrations in both BRCA1 and BRCA2, as well as for 28 other homologous recombination genes Microsatellite instability (MSI) was tested by fragment analysis, IHC and NGS. Tumor mutational burden (TMB) was measured by totaling somatic mutations (TMB-H: >10 mutations/MB). LOH cut-off >16%. Immune cell infiltrates were calculated by XCell. Differential gene expression was calculated using Limma. Significance was determined using chi-square and Wilcoxon rank sum test and adjusted for multiple comparisons (q-value < 0.05). Results: We identified 677 BRCA1mt, 439 BRCA2mt, and 7080 HRwt OC tumors. HGSOC made up the largest portion of BRCA1mt (523; 77%), BRCA2mt (306; 70%), and HRwt (4281; 60%) tumors. TP53 was most commonly mutated gene in all three groups. LOH (>16%) was highest in BRCA1mt (86.8%) compared to BRCA2mt (74.8%) and HRwt (38.4%). TMB-H was highest in BRCA2mt (6.29%) than in BRCA1mt (1.35%) and HRwt (0.91%) HGSOC (all q < 0.05). Expression of immune checkpoint genes CD80, CD86, CD274, CTLA4, HAVCR2/TIM3, IFNG, IDO1, LAG3, PDCD1 and PDCD1LG2 were significantly higher in BRCA1 and BRCA2 mt compared to HRwt HGSOC (FC: 1.12-1.59, q < 0.05). HRwt tumors had decreased infiltration of Activated Dendritic cells compared to BRCA1mt, and lower Macrophage M1 compared to both BRCA1mt and BRCA2mt (all q < 0.05). Additionally, T-inflamed score was higher in BRCA1mt compared to HRwt, while IFN score was higher in BRCA1mt compared to both BRCA2mt and HRwt (all q < 0.05). From 17,408 genes with measured expression. 522 (3.0%) differentially expressed genes (DEG) were found between BRCA2mt vs BRCA1mt; 1487 (8.54%) between BRCA2mt vs HRwt; and 9297 (53.4%) between BRCA1mt and HRwt HGSOC. Pathway analysis identified Fatty Acid Metabolism, Myc targets, ROS pathway, Oxidative Phosphorylation, and Wnt B-catenin signaling pathways as differentially regulated between the 3 groups. Conclusions: We describe the genomic, pathway and immunologic analyses in the largest cohort of BRCA1 and 2 mutated HGSOC to date. Both metabolic and immune response pathways are differentially regulated between the groups. Results can potentially inform targeted therapeutic studies based on unique BRCA genotype.