PIK3CA and breast cancer: The mutation frequencies of TP53 (p = 4.81 E‐23), ERBB2 (p = 1.57 E‐48) and CDK12 (p = 2.67 E‐30), TOP2A (p = 1.65 E‐05), SPOP (p = 0.00016), RARA (p = 3.74 E‐06), PIK3CA (p = 0.0402), PTK2 (p = 0.00082), and FAT4 (p = 0.0400) were significantly different among the four BC subtypes (Figure 3), and so the other genes in these four subtypes in Table S1.