PIK3CA and breast cancer: Notably, different PI3K inhibitors such as alpelisib, buparlisib, and taselisib (https://clinicaltrials.gov/ct2/show; ClinicalTrials.gov Identifier: NCT02437318, NCT01610284, and NCT02340221) are being administered as novel therapeutic drugs in phase III clinical trials for the treatment of breast cancer AI resistance (Table 1).