Association of obesity with breast cancer outcome in relation to cancer subtypes.

11557 Background: Obesity at breast cancer (BC) diagnosis is associated with poor outcome, although the magnitude of effect in different BC subtypes is uncertain. Here we report on the association of obesity at BC diagnosis with disease-free (DFS) and overall survival (OS) in the following subtypes: (i) hormone receptor (ER/PgR) +ve, HER2-ve, (ii) HER2+ve, any ER/PgR and (iii) triple negative (TN). Methods: We searched MEDLINE, EMBASE and COCHRANE databases to December 31, 2018 and meeting presentations (past 5 years) using predefined search terms. Study eligibility, data abstraction were performed independently by two authors; those reporting hazard ratios (HR) for obesity and DFS/OS in BC subtypes were included. Using Review Manager pooled HRs were computed and weighted using generic inverse variance in fixed and random effects models (results were similar, random effects are presented). Results: Of 10,702 titles, 26 studies (108,793 patients) were included. Pooled HR for DFS for obese vs non-obese were (i) ER/PgR+ve HER2-ve 1.21 (95% Confidence interval, CI; 1.12-1.31, p < 0.00001), (ii) HER2+ve, any ER/PgR 1.16 (95%CI, 1.06-1.26; p = 0.0006) and (iii) TN, 1.13 (95%CI; 1.05-1.22 p = 0.002). Pooled HRs for OS were (i) ER/PgR+ve, HER2-ve 1.45 (95%CI; 1.30-1.62 p < 0.00001), (ii) HER2+ve any ER/PgR 1.21 (95%CI; 1.10-1.34 p = 0.0001) and (iii) TN 1.13 (95%CI, 1.04-1.23, p = 0.003).PooledHR for OS (but not DFS) were somewhat higher in observational vs interventional studies in (i) ER/PgR+ve, HER2-ve 1.57 vs 1.36, HER2+ve any ER/PgR (ii) 1.37 vs 1.09 but not (iii) TN 1.12 vs 1.22 (p = 0.21, 0.03 and 0.48, respectively). Conclusions: Obesity was associated with a worse outcome in all BC subtypes. Higher HR for OS in observational studies in (i) ER/PgR+ve, HER2- and (ii) HER2+ve any ER/PgR BC may reflect selection of healthier patients for intervention trials.