Background: Recently, we have demonstrated that BMI significantly impacts on the efficacy of anastrozole but not tamoxifen (TAM) in premenopausal breast cancer patients. As aromatase inhibitors (AIs) are a mainstay in the treatment of endocrine responsive postmenopausal breast cancer patients, it is of certain interest, if this influence of BMI on endocrine therapy is also true for the postmenopausal situation. Methods: For analysis of the ABCSG 6 and 6a trial, patients were classified as normal weight (BMI 18.5-24.9 kg/m2) or as overweight (BMI ≥25kg/m) according to WHO criteria. The underweight population was excluded from the analyses.

We retrospectively analysed the ABCSG 6 trial, which examined the efficacy of TAM versus TAM + aminoglutethimide (first generation AI) in endocrine responsive postmenopausal breast cancer patients. All patients have been censored after 60 months since the majority of patients without events have been re-randomized into trial ABCSG 6a after 5 years. Further, we retrospectively analysed the ABCSG 6a trial, which examined 3 additional years of anastrozole versus no further treatment after 5 years of endocrine treatment.

Results: 1,566 patients (311 events/214 deaths) and 477 patients (108 events/64 deaths) were included in the analyses of the ABCSG-6 trial and the ABCSG-6a trial, respectively. About two thirds of all patients in both trials were overweight and one third was normal weight. Analysing the ABCSG 6 trial, no difference in disease free survival (DFS) and overall survival (OS) between normal weight and overweight patients treated with TAM versus TAM + aminoglutethimide could be observed. Analysing the ABCSG-6a trial, normal weight patients treated with anastrozole showed a remarkable and significant reduced risk in DFS and OS compared to control (HR 0.464, 95%CI 0.242 0.842 p=0.02 and HR 0.372, 95%CI 0.16 0.863, p=0.02). In contrast, in overweight patients anastrozole compared to control did not improve DFS and OS (HR 0.991, 95%CI 0.611 1.608, p=0.97 and HR 0.871, 95%CI 0.456 1.662, p=0.67). Conclusion: BMI impacts on the efficacy of anastrozole but not tamoxifen in postmenopausal breast cancer patients. It seems that overweight patients in contrast to normal weight patients do not benefit from additional 3 years of anastrozole after 5 years of endocrine therapy.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD09-05.