BRCA1 and breast cancer: However, BRCA1 was found to be silenced through promoter methylation in 14% of sporadic basal-like and 11% of non-basal-like breast cancers, while in two special subtypes of TNBC, medullary and metaplastic breast cancer, promoter methylation was found in >60% of cases (Badve et al., 2011, Turner et al., 2007).