ESR1 and breast cancer: Mutation in KTM2C or alterations in genes belonging to the “estrogen receptor nuclear function” (ERnf) pathway (i.e., KTM2C, ESR1, GATA3, and MYC) are more frequent in patients with recurrent disease versus de novo advanced BC, while copy number gain of FGFRs (FGFR1, 2 and 3) are prevalent in patients with more aggressive disease.