PIK3CA mutation did not affect OS in metastatic BC regardless of ER status (median OS (wild-type vs. mutated): 34.9 ± 11.0 vs. 57.9 ± 12.1 (months), p = 0.269 in ER+ BC and median OS: 27.2 ± 5.9 vs. 38.7 ± 14.0 (months), p = 0.558 in ER- BC) (Figure 4C and 4D). This evidence concerns the gene ESR1 and breast cancer.