PIK3CA and breast cancer: PI3KCB has been shown to be responsible for the accumulation of PIP3 and reactivation of AKT in HER2-amplified breast cancers treated with a PI3KCA-specific inhibitor, and concomitant inhibition of PI3KCA and PI3KCB induces greater antitumor efficacy in HER2-amplified and PIK3CA mutant breast cancers [34].