Endocrine therapy in obese patients with primary breast cancer: another piece of evidence in an unfinished puzzle

Obesity, defined as a body mass index (BMI) ≥30 is an independent risk factor in breast cancer and is correlated with shorter survival and enhanced recurrence rates. The present subgroup analysis of the German BRENDA-cohort aimed to investigate the correlation between BMI, recurrence-free survival (RFS) and adjuvant endocrine therapy. In this subgroup analysis, 4,636 patients were retrospectively examined using multivariate analyses. Overall 3,759 (81.1%) patients had a BMI <30 (non-obese) and 877 (18.9%) a BMI ≥30 (obese). In the group of all 3,896 (84.0%) patients with hormone-receptor-positive (HR+) breast carcinomas a significant reduction in RFS was demonstrated for those who were obese (P = 0.002; HR = 1.45 (95% CI: 1.15–1.83)), also after adjustment for Nottingham Prognostic Index (NPI) (P = 0.028; HR = 1.30 (95% CI: 1.03–1.65)). In hormone-receptor-negative (HR−) patients BMI had no influence on RFS (P = 0.380; HR = 1.20 (95% CI: 0.80–1.81)). Considering menopausal status, a significantly shorter RFS was seen in postmenopausal obese than in non-obese patients (P < 0.001; HR = 1.61 (95% CI: 1.24–2.09)), whereas the premenopausal patient group only showed a trend towards a shorter RFS (P = 0.202; HR = 1.44 (95% CI: 0.82–2.53)). The group of HR+ postmenopausal patients with normal or intermediate weight showed a non-significant statistical trend towards a survival benefit for aromatase inhibitors (AI) compared to tamoxifen (RFS: P = 0.486; HR = 1.29 (95% CI: 0.63–2.62), while obese patients tended to benefit more from tamoxifen (RFS: P = 0.289; HR = 0.65 (95% CI: 0.29–1.45)). In accordance with recently published results we demonstrated a negative effect of a high BMI on outcome in primary breast cancer. Furthermore the efficacy of AI seems dependent on BMI in contrast to tamoxifen. Prospective studies to optimise the therapy of obese breast cancer patients are urgently needed.