Does Switching from Tamoxifen to an Aromatase Inhibitor Result in Weight Change in Postmenopausal Breast Cancer Patients

Background: Women treated with early stage breast cancer often gain weight following diagnosis. Tamoxifen and aromatase inhibitor (AI)-treated patients experience similar weight gains in randomized clinical trials after five years of adjuvant therapy. How switching therapies affects weight change is uncertain. Purpose: To determine the degree of weight change at the time of switching from tamoxifen to an aromatase inhibitor during adjuvant hormonal therapy, and to identify possible associations. Methods: Retrospective review of postmenopausal women with non-metastatic, invasive, hormone receptor-positive breast cancer sequenced from tamoxifen to an AI. Weights and height were recorded while on tamoxifen, 12 and 6 months prior to switching, at the time of the switch and 6 and 12 months post-switch. Variables included age at diagnosis, adjuvant chemotherapy, body-mass index (BMI), antidepressant use, co-morbidities, and menopausal status. Results: Data on 80 eligible patients revealed mean weight change from 12 months prior to 12 months post-switch was 0.7 kg (95%CI: -0.16, 1.5 kg, p=.11) with most of the change occurring before the switch. No significant difference was found between weights obtained from the time of switch to 12 months after (mean change -0.1 kg; 95% CI: -0.74, 0.53, p=.75). No association with age, stage, BMI, menopausal status, specific AI, duration of tamoxifen, adjuvant chemotherapy, alcohol or antidepressant use was found. Conclusions: While patients switching from tamoxifen to an AI experienced modest weight gain in the 12 months prior to the switch, they did not experience further significant weight change after 12 months on an AI.