The impact of body size changes on recurrence risk depends on age and estrogen receptor status in primary breast cancer

Purpose To investigate the prognostic impact of body size changes during the first postoperative year in breast cancer. Methods A cohort of 1,317 primary breast cancer patients included in Sweden (2002–2014) underwent body size measurements at the preoperative and 1-year visits (n = 1,178). Landmark survival analyses were used to investigate how postoperative weight gain or loss (> 5%) or change in waist–hip ratio (WHR) categories (≤ 0.85 or > 0.85) impact prognosis. Results Median age at inclusion was 61 years and body mass index 25.1 kg/m2. After a median follow-up of 5.0 years from inclusion, 165 recurrences and 77 deaths occurred. Weight gain (17.0%) conferred over twofold recurrence risk only in patients Pinteraction = 0.033). Weight loss (8.6%) was only associated with a poor prognosis in patients ≥ 70 years, but not after restriction analysis. Weight change did not impact prognosis in patients 50 to Pinteraction = 0.007), with higher recurrence risk in patients with ER+ tumors and lower recurrence risk with ER− tumors. Conclusion Both changes in terms of weight and WHR category yielded independent prognostic information. Further research is imperative before recommending weight loss for all overweight breast cancer patients.