ESR1 and cancer: PIK3CA, the catalytic subunit of PI3-kinase, is frequently mutated in a diverse range of cancers including breast, endometrial and cervical cancers, and the alpha-isoform selective PI(3)-kinase inhibitor alpelisib and the pan-AKT kinase inhibitor capivasertib, each in combination with fulvestrant, are FDA-approved for the treatment of patients with PIK3CA mutant ER+/HER2- metastatic breast cancer [32, 33].