TP53 and breast cancer: One possible explanation may have to do with differences in the timing of TP53 mutations in different breast cancer subtypes.26 Limited evidence from one study on BRCA1 mutated breast tumors suggested that in contrast to basal-like tumors in which TP53 mutations occur late, TP53 mutations may occur early in the development of luminal A tumors.26 Nonetheless, the relatively small number of p53− cases in the other subtypes may have led to reduced power to detect significant differences.