In P1, FGFR3 (p.S249C and p.L377R) and KDM6A (p.S1114L) missense mutations and one truncating mutation of KMT2D (p.E4670*) were observed as clonal mutations, indicating that the mutational makeup for BC tumorigenesis was established early in this patient. Here, KDM6A is linked to breast cancer.