Contributing to heterogeneity, several genes are mutated, amplified, or deleted in various subtypes of BC and can be considered as drivers, the top 10 most frequent being: TP53, PIK3CA, MYC, CCND1, PTEN, ERBB2, ZNF703/FGFR1 locus, GATA3, RB1 and MAP3K1 (6). The gene discussed is CCND1; the disease is breast cancer.