An Observational Study to Assess Response to Tamoxifen in Breast Cancer Patients

CYPTAM-BRUT 2 is a prospective, multicentric study including postmenopausal women receiving tamoxifen for metastatic, locally advanced (stage IIIB/C) or in the neoadjuvant setting for measurable estrogen-receptor positive breast cancers. The primary endpoint is the difference in efficacy of tamoxifen, defined as the objective response rate using RECIST criteria, between women with a normal versus low Tamoxifen Activity Score (TAS) after 3-6 months of tamoxifen use. The TAS score is based on the presence of genetic variations and drug interactions. Secondary endpoints are time to progression, clinical benefit, serum metabolite concentrations, endometrial changes and menopausal symptoms. Patients using tamoxifen in the neoadjuvant setting needs being operated between 4-6 months following the start of tamoxifen.