PIK3CA and breast cancer: The phosphoinositide 3‐kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) (PI3K/AKT/mTOR) signaling pathway is the most commonly mutated pathway in HR‐positive breast cancer, and abnormal activation of this pathway is highly correlated with resistance to endocrine therapy [75].