BRCA1 and breast cancer: Stratifying for BC subtype in YA (Fig. 3), the most frequently altered genes consisted of TP53 (39 %), ESR1 (27 %), PIK3CA (25 %), FGFR3 (18 %), FGRF4 (18 %), FGFR19 (18 %), CCND1 (18 %) for HR + BC and TP53 (100 %), PTEN (26 %), BRCA1 (22 %), RB1 (17 %), for triple negative BC.