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Individuals with germline mutations in the  BRCA1  gene have an elevated risk of developing breast cancer, and often display characteristic clinicopathological features. We hypothesised that inactivation of  BRCA1  by promoter methylation could occur as a germline or an early somatic event that predisposes to breast cancer with the phenotype normally associated with  BRCA1  germline mutation.    Methods  We examined seven cases from breast-ovarian cancer families with tumours that showed  BRCA1 -like pathology but did not have detectable  BRCA1  or  BRCA2  germline mutations present. Methylation levels were tested by several quantitative techniques including MethyLight, methylation-sensitive high resolution melting (MS-HRM) and a newly developed digital MS-HRM assay.    Results  In one patient, methylation of 10% of the  BRCA1  alleles was detected in the peripheral blood DNA, consistent with 20% of cells having one methylated allele. Buccal mucosa DNA from this individual displayed approximately 5%  BRCA1  methylation. In two other patients, methylation of  BRCA1  was detected in the peripheral blood at significantly lower but still readily detectable levels (approximately 1%). Tumour DNAs from these three patients were heavily methylated at  BRCA1 . The other patients had no detectable  BRCA1  methylation in their peripheral blood. One of seven age-matched controls showed extremely low levels of methylation in their peripheral blood (approximately 0.1%).    Conclusion  These results demonstrate that in some cases of breast cancer, low-level promoter methylation of  BRCA1  occurs in normal tissues of the body and is associated with the development of  BRCA1 -like breast cancer.

BRCA1 promoter methylation in peripheral blood DNA of mutation negative familial breast cancer patients with a BRCA1tumour phenotype