BRCA1 expression, its correlation with clinicopathological features and response to neoadjuvant chemotherapy in high grade serous ovarian cancer from an Indian centre

In high grade serous ovarian cancers (HG-SOC), BRCA1/2 mutations have been reported as the most predominant mutations by various studies. However, the non-mutational mechanisms of BRCA pathway inactivation in HG-SOC are unclear. We aimed to evaluate BRCA1 inactivation by estimating its expression along with its repressor in primary and neoadjuvant chemotherapy (NACT) treated HG-SOC tumors with known therapeutic response. The expression pattern of BRCA1 protein was evaluated by immunohistochemistry (IHC) in 119 cases of HG-SOC from a hospital cohort consisting of primary (N= 69) and NACT treated (N=50) tumors. Histological patterns (SET), stromal infiltration by lymphocytes (sTILs) and chemotherapy response score (CRS) were estimated by microscopic examination. Gene expression levels of BRCA1, and its repressor ID4 was estimated by qPCR. Association of BRCA1 protein and mRNA with clinicopathological features was studied. Relevance of the BRCA1/ID4 ratio was evaluated in tumors with different CRS. BRCA1 protein expression was observed in 12% of primary and 19% of NACT treated HG-SOC tumors. Moderate concordance was observed between BRCA1 protein and mRNA expression (AUC-0.677). High BRCA1 mRNA expression was significantly associated with more frequent SET pattern (p=0.024), higher sTILs density (p=0.042), increased mitosis (p=0.028). BRCA1 negative tumors showed higher expression of ID4 though not statistically significant. Higher BRCA1/ID4 ratio was associated with high sTILs density in primary (p=0.042) and NACT treated tumors (p=0.040). Our findings show the utility of BRCA1/ID4 ratio to predict neoadjuvant therapy response, which needs further evaluation in larger cohort with long term outcomes.