TP53 and breast cancer: In this analysis, TP53 mutation was more frequently detected in ER-negative BC (ER-positive vs. ER-negative: 41.7% vs. 92.6% p < 0.001) and PIK3CA mutation was more common in ER-positive BC (ER-positive vs. ER-negative: 47.2% vs. 18.5%, p = 0.018) (Figure 1D).