104P Obesity and recurrence in postmenopausal, estrogen-receptor-positive breast cancer patients treated with adjuvant aromatase inhibitors: A Danish population-based cohort study

Clinical studies confirm that obesity is a key risk factor for recurrence in postmenopausal women with estrogen receptor (ER)-positive breast cancer. Concerning evidence suggests that women with obesity do not obtain similar protection from aromatase inhibitors (AI) as healthy-weight women. We examined a cohort of postmenopausal women diagnosed with stage I-III ER+ breast cancer from 1998-2016, treated with AIs in the adjuvant setting. The study was conducted using data from the Danish Breast Cancer Group and information on height and weight was supplemented with data from the Danish Anesthesiology database. Body mass index (BMI) was classified as I) healthy-weight (18.5-24.9 kg/m2), II) overweight (25-29.9 kg/m2), III) obesity (30-34.9 kg/m2), and IV) severe obesity (≥ 35 kg/m2) using the World Health Organization guidelines. Follow-up began six months after breast cancer surgery and continued to the first event of recurrence, contralateral breast cancer, another malignancy, death, emigration, end of clinical follow-up, or 25th September 2018. We used Cox regression to estimate crude and adjusted hazard ratios (HRs) with 95% confidence intervals (95% CI). The model was adjusted for patient, tumor and treatment characteristics. From the original 44,449 eligible patients, we enrolled patients who were postmenopausal, had ER-positive breast cancer, were treated with AIs, and had information on BMI (N=13,261). There were 442 recurrences over 37,668 person-years of follow-up among patients with healthy-weight, 339 recurrences in 27,061 person-years among patients with overweight, 165 recurrences in 11,843 person-years in patients with obesity and 82 recurrences in 5,234 person-years in patients with severe obesity. Multivariable analyses revealed increased recurrence hazards associated with overweight (HR: 1.09 [95% CI: 0.95-1.26]), obesity (HR: 1.22 [95% CI: 1.02-1.46]) and severe obesity (HR: 1.42 [95% CI: 1.12-1.80]), compared with healthy-weight. Obesity was associated with an increased risk of breast cancer recurrence among postmenopausal ER+ early-stage breast cancer patients treated with AIs.