ESR1 and breast carcinoma: Researchers also evaluated the relationship between PFS in patients treated with alpelisib plus fulvestrant/letrozole and ESR1 mutations detected via ctDNA, finding no interaction in Cohorts A or C.2,5 In contrast, in Cohort B, there was a numerical trend toward ESR1 mutations and shorter PFS.5 These findings suggest that treatment with alpelisib plus fulvestrant may be the preferred option for patients with HR-positive, HER2-negative, PIK3CA-mutated advanced breast cancer when the presence of an ESR1 mutation is suspected.