COMPARING THE EFFECTS OF AROMATASE INHIBITORS AND SELECTIVE OESTROGEN RECEPTOR MODULATORS ON BODY COMPOSITION, EXERCISE TOLERANCE AND MARKERS OF CARDIOVASCULAR RISK IN FEMALES WITH BREAST CANCER

INTRODUCTION Adjuvant endocrine therapy (AET) blocks the action of estrogens and is commonly prescribed in hormone receptor-positive breast cancer. Given the putative cardioprotective role of estrogens in females, AET may exacerbate the negative metabolic side-effects of anthracycline chemotherapy. This study examined the early effects of combined anthracycline chemotherapy and AET on body composition, exercise tolerance and markers of cardiovascular risk in a cohort of females with breast cancer. METHODS This was a secondary analysis of the BReast cancer EXercise InTervention (BREXIT) Trial. Females with breast cancer (n=105, aged 51 ± 8 years, BMI 27.4 ± 5.1, mean ± SD) scheduled for anthracycline chemotherapy participated in this study. Aerobic exercise capacity, body composition, physical function, and blood pressure were measured before anthracycline treatment and after 4- and 12-months follow-up. Linear mixed models assessed whether aromatase inhibitors (AI) or selective estrogen receptor modulators (SERMS) affected exercise tolerance, body composition and markers of cardiovascular risk compared to non-endocrine breast cancer treatments. RESULTS Twelve months of anthracycline treatment combined with AI or SERMs decreased total body lean mass by 1.4 kg (2%; interaction p=0.01) and 1kg (1%; interaction p=0.16) respectively, when compared to non-endocrine therapies. There were trends for AET to decrease total fat (-1.5%, interaction p=0.05) and android fat (-2.3%, interaction p=0.07) mass compared to non-endocrine therapy after 12 months. AIs significantly increased both systolic (5.8mmHg, interaction p=0.05) and diastolic (4.0mmHg, interaction p=0.05) blood pressure after 12 months of treatment compared to SERMs or non-endocrine therapies. There was no effect of either AET or SERMS on VO2peak, leg press or seated row 1RM, 30 second sit to stand or handgrip strength. DISCUSSION AND CONCLUSION Short-term treatment with adjuvant endocrine therapies may accelerate muscle loss and increase blood pressure compared to non-endocrine therapies. However, these changes were not associated with worsening of physical function.