PIK3CA and breast cancer: The TIMER database was used to determine differences of PIK3CA expression in tumor and normal tissues across various type of cancers, which demonstrated low PIK3CA mRNA expression in breast cancer, colorectal cancer, KIRC, KIRP, hepatocellular cancer, lung adenocarcinoma, prostate adenocarcinoma, and uterine corpus endometrial carcinoma (Figure 1(a)).