CYPTAM-BRUT 2: A prospective multicenter observational study in the neoadjuvant and metastatic setting investigating tamoxifen response between women with a favorable versus unfavorable endoxifen profile.

Abstract

TPS140 Background: Tamoxifen is widely used to treat hormone receptor positive breast cancers, in the (neo-)adjuvant setting as well as in the metastatic setting. Even though tamoxifen saved many lives worldwide, a lot of variation in clinical response and side effects is observed between women. One hypothesis is variation in the metabolism of tamoxifen through cytochrome P450 enzymes, which are needed to convert tamoxifen in the more active metabolite endoxifen. Several retrospective studies have been performed but results remain contradictory. This can be explained in part by the retrospective nature of all studies, selection bias, different inclusion criteria and different objectives between the studies, making them difficult to interpret and compare. Methods: This is a prospective multicentre open label single arm non randomized observational study (NCT00965939) including postmenopausal women receiving tamoxifen as first line therapy in the metastatic or neo-adjuvant setting. Prior endocrine therapy in the adjuvant setting is allowed if there is more than 12 months after completion of the adjuvant therapy. Primary objective is to analyse tumor response by endoxifen plasma concentrations. Secondary objectives are 1) efficacy in terms of the proportion of patients who are progression free at 6 months, 2) efficacy in terms of clinical benefit (CR + PR + SD), 3) tolerability of tamoxifen and 4) predictive value of the tamoxifen activity score, based on tamoxifen pharmacogenetics and interacting drugs. Patients with bone only lesions and no other measurable lesions will not be included in the analysis of the primary objective. Total sample size is 260 and currently (31-01-2011) we included 100 patients from 20 participating centres. Other collaborative groups consider to join this protocol.