DNA methylation of the immediate upstream region of BRCA1 major transcription start sites is an independent favorable prognostic factor in patients with high-grade serous ovarian cancer
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To establish a quantitative method to evaluate the DNA methylation level of an immediate upstream region of major BRCA1 transcriptional start sites (TSSs), and to investigate whether methylation of the region is a prognostic factor in high-grade serous ovarian cancer patients after neoadjuvant chemotherapy. Ninety-two FFPE samples of advanced high-grade serous ovarian cancers after neoadjuvant chemotherapy between 2011 and 2018 were used for mutation and methylation analysis. DNA methylation levels were assessed by pyrosequencing and DNA methylation microarray. An association between methylation level (or a mutation) and progression-free survival was assessed by Kaplan-Meier analysis. Major BRCA1 transcripts and CpG sites immediately upstream of their TSSs were identified, and a pyrosequencing method was developed. BRCA1 methylation, BRCA1/2 mutations, and a RAD51C mutation were detected in 17/79 (21.5%), 17/92 (18.5%), and 1/92 (1.1%) high-grade serious ovarian cancer samples. In univariate analysis, BRCA1 methylation and no residual tumor were associated with progression-free survival (BRCA1 methylation: P = 0.025, no residual tumor: P = 0.0026). Multivariate analysis showed that both BRCA1 methylation (P = 0.038, HR = 0.47, 95% CI: 0.21-0.96) and no residual tumor (P = 0.012, HR = 0.49, 95% CI: 0.28-0.85) were significant favorable prognostic factors. A quantitative method to estimate the methylation level of the immediate upstream region of major BRCA1 TSSs was established. Methylation of the region of was an independent favorable prognostic factor in high-grade serous ovarian cancer patients.