Purpose: This study was performed to characterize the impact of obesity on the risk of breast cancer recurrence and death as a result of breast cancer or other causes in relation to adjuvant treatment.
Patients and methods: Information on body mass index (BMI) at diagnosis was available for 18,967 (35%) of 53,816 women treated for early-stage breast cancer in Denmark between 1977 and 2006 with complete follow-up for first events (locoregional recurrences and distant metastases) up to 10 years and for death up to 30 years. Information was available on prognostic factors and adjuvant treatment for all patients. Univariate analyses were used to compare the associations of known prognostic factors and risks of recurrence or death according to BMI categories. Cox proportional hazards regression models were used to assess the influence of BMI after adjusting for other factors.
Results: Patients with a BMI of 30 kg/m(2) or more were older and had more advanced disease at diagnosis compared with patients with a BMI below 25 kg/m(2) (P < .001). When data were adjusted for disease characteristics, the risk of developing distant metastases after 10 years was significantly increased by 46%, and the risk of dying as a result of breast cancer after 30 years was significantly increased by 38% for patients with a BMI of 30 kg/m(2) or more. BMI had no influence on the risk of locoregional recurrences. Both chemotherapy and endocrine therapy seemed to be less effective after 10 or more years for patients with BMIs greater than 30 kg/m(2).
Conclusion: Obesity is an independent prognostic factor for developing distant metastases and for death as a result of breast cancer; the effects of adjuvant therapy seem to be lost more rapidly in patients with breast cancer and obesity.