In this study, we found high prevalence of mutations of KRAS, PIK3CA, MAP3K1, MAP2K4, PTEN, TP53, CDH1, GATA3, KMT2C, ARID1A, RunX1, and ESR1 genes occurring in primary tumor specimens of BC patients, including triple-negative and luminal A patients. The gene discussed is KMT2C; the disease is breast cancer.