A total of 12 genes in descending order of mutation frequency (AKT1, CBFB, CDH1, CDKN2A, ESR1, GATA3, MAP2K4, MAP3K1, PIK3CA, PTEN, RB1 and TP53) were significantly mutated in mBC over non-metastatic tumors, and eight additional genes (AGR, EDC4, ESR1, FRAS1, FSIP2, IGFN1, OSBPL3 and PALB2) displayed higher mutation frequencies in mBCs than non-metastatic tumors. This evidence concerns the gene MAP2K4 and metastatic neoplasm.