Tumor mutational load in gynecological and breast cancer.

Abstract

44 Background: Lack of test standardization and conflicting results on PD1 and PD-L1 immunohistochemistry (IHC) assays challenge their use as predictive biomarkers for checkpoint inhibitors. High tumor mutational load (TML) has been linked to therapeutic response with immune checkpoint inhibition in melanoma, lung and colorectal cancer. Herein, we explore association of TML and PD1/PD-L1 expression in gynecological (GC) and breast cancer (BC). As secondary aim we explore the association of TML with BRCA1/2 mutations. Methods: De-identified data from molecular profiling on GC and BC tumors from the CARIS Life Sciences database was analyzed after obtaining IRB approval. TML was defined as the total number of nonsynonymous, somatic mutations per Mb sequenced with a 592-gene panel. PD-1 IHC was tested on Tumor Infiltrating Lymphocytes (TIL) with the cutoff of 1/HPF; PD-L1 expression was measured on tumor cells with the cutoff of 2+, 5%. Biomarker association was tested with ANOVA test (SPSS v23, IBM). Results: As shown in table, cervical (CC) and endometrial cancers (EC) had the highest TML and squamous CC and triple negative BC (TNBC) tumors with highest PD-L1. In EC, MSI-H was associated with higher TML when compared to MSS (20.1 vs. 6.1, p<0.001); 4 POLE-mutated tumors all carried TML (36-678) higher than mean (11.5). TML was not associated with PD1 or PDL1 positivity in any of the diseases. BRCA1/2 mutations were associated with higher mean TML in ovarian cancer (OC) (6.8 vs. 5.4 in wild type, p<0.001) but not in BC (6.3 vs. 6.8 in wild type, p=0.48). Conclusions: In this sample of patients who underwent molecular profiling, there was no association between TML and PD1 or PD-L1 expression. Association between BRCA1/2 tumor mutations and TML in OC is worth exploring. High TML in CC and EC support the development of immunotherapy for these diseases. [Table: see text]