ESR1 and breast cancer: In a randomised, phase 3 trial, alpelisib, a selective inhibitor of the p110α catalytic subunit of PI3K, encoded by the PIK3CA gene, in combination with the ER antagonist fulvestrant, prolonged progression-free survival for PIK3CA-mutated, ER+, HER2-negative, advanced breast cancers that had previously received endocrine therapy [8].