Body Mass Index and Outcomes in Breast Cancer Treated With Breast Conservation

Obesity is increasing in incidence in New Zealand. Maintaining locoregional control after breast cancer surgery is important, as this can improve overall survival. Although obesity has been associated with poorer survival in breast cancer, the correlation with locoregional control is less well evaluated and was the subject of this evaluation.

We used the New Zealand breast cancer registry to identify patients treated with breast conservation with body mass index (BMI) recorded. We retrieved patient demographic, tumor characteristic, and treatment-related information. We assessed local and locoregional control outcomes in addition to breast cancer and overall survival outcomes.

Patients (2513) were identified. The median follow-up was 5.25 years. Of these patients, 38% were obese with a BMI of ≥30 kg/m², 32% were overweight with a BMI of 25.0 to 29.9 kg/m², and 29% were either normal or underweight with a BMI of ≤24.9 kg/m². Most patients were postmenopausal (65%). The median tumor size was 16.0 mm (0.2-80 mm) and the majority were grade 2 or 3 tumors (45% and 33%). The majority (66%) were pathologically node negative and lymphovascular invasion was seen in 24%. There were 81% with estrogen receptor positivity and 358 (14.2%) were Her-2 positive. Local relapse free survival at 5 years was 91.5% (95% confidence interval [CI], 90.3-92.7) and at 10 years was 78.5% (95% CI, 75.9-81.1). Local relapse free rate at 5 years was 96.8% (95% CI, 96.0-97.6) and 10 years was 93.9% (95% CI, 92.5-95.3). We did not find BMI to be associated with local or locoregional relapse, disease free, breast cancer specific, or overall survival.

Obesity was not associated with inferior locoregional control or survival outcomes. This supports the practice of continuing to offer breast conserving treatment to women regardless of BMI.