PIK3CA and breast cancer: Although there is no consensus about a predisposition of PIK3CA mutation by breast cancer subtype, several studies have reported that 13.3% to 61.5% of HR+/HER2– ABC tumors and 12% to 25% of HER2+ tumors had PIK3CA mutations, whereas triple-negative breast cancer harbors the lowest rates of PI3KCA mutations (20, 21).