ESR1 and breast cancer: Undetected metastasis-specific mutations in likely breast cancer drivers included genes that are frequently mutated in primary breast cancer (PIK3CA, TP53, KMT2C, AKT1, CCND1, CDKN1B, RB1, RHOA, RUNX1) [24], as well as genes that have been reported to be frequently and preferentially mutated in metastases (ESR1, ERRB2, XIRP2, PEAK1, MYLK, FLT4, RHOA, RICTOR, TP53) [6, 7].