CLINICAL TRIAL Weight change associated with anastrozole and tamoxifen treatment in postmenopausal women with or at high risk of developing breast cancer Ivana Sestak • Michelle Harvie • Anthony Howell • John F. Forbes • Mitch Dowsett • Jack Cuzick Received: 15 March 2012 / Accepted: 27 April 2012 Ó Springer Science+Business Media, LLC. 2012 Abstract Weight gain is commonly reported by breast cancer patients on tamoxifen or aromatase inhibitors. Since weight gain may impact on outcome and compliance we have prospectively assessed the effects of these agents on weight change in three randomised trials for the treatment or prevention of breast cancer. Data on weight change in postmenopausal women from three large clinical trials investigating endocrine therapy for the treatment or pre- vention of breast cancer were analysed (ATAC, IBIS-I and IBIS-II). In the IBIS-I study, mean weight change on tamoxifen was ?0.1 kg (SD 0.1) compared with ?0.3 kg (SD 0.1) in women taking the placebo (P = 0.3) between baseline and 12 months of follow-up. In the IBIS-II trial, no statistically significant difference was found between anastrozole and placebo after 12 months of follow-up [?0.8 kg (SD 5.3) vs. ?0.5 kg (SD 7.4), P = 0.5]. In the ATAC trial, no statistically significant differences in weight gain between anastrozole and tamoxifen were found after 12 months of follow-up [?1.4 kg (SD 3.9) vs. ?1.5 kg (SD 4.0), P = 0.4]. Significant baseline predictors for gaining more than 5 kg of weight after 12 months of follow-up were: being younger than 60 years old, smoking and mastectomy. All three trials demonstrate that weight gain occurs primarily within the first 12 months of active treatment in a subset of patients. In the prevention trials, weight gain does not differ between anastrozole, tamoxifen and placebo and also did not differ between anastrozole and tamoxifen in the treatment trial. Keywords Breast cancer Á Weight changes Á Endocrine treatment Introduction Weight gain is commonly reported by breast cancer patients after diagnosis. Gains are greatest amongst patients receiving adjuvant chemotherapy (3–7 kg) [1–3] and are on average more modest with adjuvant endocrine therapy (1–2 kg) [4]. However, subsets of patients gain a signifi- cant amount of weight on endocrine therapy [5]. Patients taking tamoxifen or anastrozole perceive these agents to cause weight gain, which is a major concern [6, 7] and may limit persistence to these agents. Excess weight at diag- nosis [8, 9] and weight gain during treatment has been associated with an increased relapse rate and poorer sur- vival [10–14]. Most reports on weight gain with tamoxifen [2, 15–17] do not have a no-treatment comparison group, making it difficult to attribute the weight gain entirely to tamoxifen. However, no weight gain with tamoxifen was observed in Presented at the 2011 ASCO Breast Cancer Symposium, San Francisco, CA, September 13–15 2011. I. Sestak (&) Á J. Cuzick Centre for Cancer Prevention, Wolfson Institute of Preventive Medicine, Queen Mary University, Charterhouse Square, London EC1M 6BQ, UK e-mail: i.sestak@qmul.ac.uk M. Harvie Á A. Howell Nightingale Screening Centre and Genesis Prevention Centre, University Hospital of South Manchester Wythenshawe, Manchester, UK J. F. Forbes School of Medical Practice and Population Health, University of Newcastle, Newcastle, Australia M. Dowsett Department of Academic Biochemistry, Royal Marsden Hospital, London, UK 123 Breast Cancer Res Treat DOI 10.1007/s10549-012-2085-6