Body mass index and risk of recurrence and mortality of luminal, triple-negative, and HER2- overexpressing breast cancer

Abstract

Breast cancer is a leading cause of death of women worldwide, and there is an understanding that risk factors for breast cancer recurrence and mortality differ by subtype. The most common subtypes are: luminal (estrogen receptor positive and/or hormone receptor positive), estrogen receptor negative and her2-overexpressing (H2E), and triple negative (TN). Overweight and obesity, as measured by body mass index (BMI), has been suspected to be associated with an increased risk of breast cancer recurrence and mortality but results have been inconsistent by subtype. We conducted a longitudinal cohort study to assess the association between BMI and breast cancer recurrence and breast cancer specific mortality (BCSM), stratified by breast cancer subtype using multi-variable adjusted Cox proportional hazards models. Our population consisted of 1,938 luminal (156 recurrences, 173 breast cancer deaths), 686 H2E (59 recurrences, 60 deaths), and 1,193 TN (260 recurrences, 273 deaths) patients. Mean follow up time was 4.1 years for recurrence and 10.4 years for BCSM. Compared to normal weight women, neither overweight nor obesity was associated with a significantly increased risk of recurrence for luminal subtype, (HR=1.15, 95% CI 0.78-1.71 and 1.23, 95% 0.84-1.79, respectively), while obesity (HR= 2.21, 95% CI 1.13-4.32), but not overweight (HR=1.42, 95% CI 0.70-2.88) was associated with recurrence in H2E patients. Overweight (HR=0.61, 95% CI 0.44-0.85) was inversely associated with recurrence in patients with TN breast cancer, while no association was observed for obese patients (HR=0.89, 95% CI 0.67-1.19). The pattern of results by subtype for BCSM was similar to that observed for recurrence. These findings add to the literature on associations between BMI and subtype specific recurrence and mortality risks and provides further evidence that associations differ by subtype, with moderate to strongly positive associations for obesity in H2E patients, and weaker associations for other subtypes.