ESR1 and breast cancer: In a pharmacogenetic analysis of the Tamoxifen Exemestane Adjuvant Multinational (TEAM) study an association between tamoxifen efficacy and the rs2234693 SNP in the estrogen receptor-1 (ESR1) gene has been found in postmenopausal hormone receptor positive breast cancer patients, whereas patients with an increasing number of C alleles of PvuII in ESR1 had a decreased disease free survival (DFS)9.