PIK3CD and breast cancer: In addition, mutations in the PIK3CA gene leading to hyperactivation of the p110α PI3K catalytic subunit have been reported to occur in 30–40% of patients with ER+ BC and in 20–25% of BC patients with overexpression of ERB2, and mutations in Akt1 and PTEN have been found in 13–24% and 7% of ER+ BC patients, respectively [31,33,35].