While the number of cases in the present study is limited, our finding that constitutional BRCA1 methylation may account for 19.4% of all triple-negative and ER-low breast cancers is high given the observed BRCA1 methylation frequency in the population (5.6% among non-cancer females in the US [26], 8.0% among young mothers and 9.0% among healthy newborns in the current study). Here, BRCA1 is linked to cancer.