Mutational landscapes and tumour mutational burden expression in endometrial cancer

Abstract

Background: Endometrial cancer (EC) is one of the most common gynaecological tumours. Tumour mutational burden (TMB) has emerged as a promising predictor to evaluate efficacy to immunotherapy in several kinds of solid tumours. However, the relationship between TMB and genetic features of EC remains unclear. Methods: Total 50 EC patients including 41 endometrioid adenocarcinoma, 6 uterine serous adenocarcinoma, 1 uterine clear cell carcinoma, 1 endometrial squamous cell carcinoma and 1 endometrial adenosquamous carcinoma were enrolled in this study. The ECs had been classified as FIGO I (n=14), II (n=6), III (n=12), IV (n=16) and not available (n=2). FFPE tumour and matched blood samples were collected from patients for NGS-based targeted panel sequencing (450 genes). Genomic alterations and TMB were assessed. Results: The 50 patients had a median age of 56 years (range, 32-73 years) with a median TMB of 3.8 muts/Mb (interquartile range (IQR), 1.5-13.7 muts/Mb). We found recurrent mutations, including PTEN (64%), PIK3CA (44%), ARID1A (40%), PIK3R1 (36%), TP53 (32%), CHD4 (20%), and KRAS (20%). FGFR2 mutations were occurred in 7 (14%) patients. The most frequently mutated genes in early-stage (FIGO I and II) were PTEN (85%), ARID1A (50%), PIK3R1 (50%), PIK3CA (40%), LRP1B (30%), and CHD4 (30%), while the most common mutations in advanced-stage (FIGO III and IV) were PTEN (46%), PIK3CA (43%), TP53 (43%), ARID1A (36%), PIK3R1 (29%), and KRAS (21%). We also found that all POLE mutations (5/5) occurred in early-stage. Mutations of PIK3R1, CHD4, CTCF, SETD2, PPP2R1A, NF1, BRCA2, ARID1B and POLE were associated with TMB-high (TMB-H, TMB≥10muts/ Mb) (P<0.05 for all). Importantly, all POLE mutations occurred in EC with TMB-H, including two cases of EC with ultrahigh TMB (TMB > 100 muts/Mb). At least one actionable mutation was identified in 86% (43/50) patients. Conclusions: PI3K signaling pathway genes, PTEN, PIK3CA and PIK3R1 were most frequently mutated in EC. 26% patients (13/50) had TMB-H. POLE mutations likely occurred in early stage and were related with TMB-H, which may provide potential targets for immunotherapy of EC.