A study examining the association of treatment outcome and body mass index (BMI) among breast cancer patients receiving adjuvant therapy found no difference in terms of benefit from therapy based on patients’ BMI. The results are published in the Journal of Clinical Oncology.
While obese breast cancer patients (BMI > 30 kg/m2) had a slight disadvantage in terms of overall survival (hazard ratio [HZ] = 1.19) compared to patients with a normal body weight (BMI < 25 kg/m2), no difference in overall survival was detected between normal BMI and overweight patients (HZ = 1.02).
Early breast cancer patients treated with either 5-year adjuvant letrozole(Drug information on letrozole) or tamoxifen(Drug information on tamoxifen) monotherapy in the Breast International Group I-98 trial were followed for a median of 8.7 years. Marianne Ewertz, MD, of the department of oncology at the Odense University Hospital and University of Southern Denmark, and colleagues examined whether BMI was associated with differential disease-free survival, overall survival, and distant recurrence-free interval. Half of the 4,780 patients in the study received letrozole and half were treated with tamoxifen.
While studies have shown obesity is a prognostic factor of early-stage breast cancer, it is not clear how obesity can influence the biology of breast cancer or whether it affects its treatment. It also not clear whether BMI can influence the efficacy of different adjuvant therapies—chemotherapy or hormonal therapy. The Arimidex, Tamoxifen Alone or in Combination (ATAC) trial showed tamoxifen to be effective for all breast cancer patients while anastrozole(Drug information on anastrozole) was found to be less effective in postmenopausal breast cancer patients who were overweight (BMI > 30 kg/m2). The authors of this previous study had suggested that anastrozole, which suppresses estrogen, may not work as efficiently in breast cancer patients who are obese. Data from another trial, the Austrian Breast and Colorectal Cancer Study Group (ABCSG) 12 trial had similar results. The 2011 study found premenopausal women who were overweight had a poorer overall survival compared to normal-weight women in the study. All patients were treated with goserelin(Drug information on goserelin) in combination with anastrozole.
The current Breast International Group I-98 trial shows that obese breast cancer patients have a poorer overall survival compared to their normal weight counterparts—obese patients are more likely to have a distant recurrence. The results provide further evidence that obesity is an independent negative prognostic factor for death from breast cancer. However, treatment outcomes in both the tamoxifen and letrozole groups were similar regardless of whether the patient was obese or of normal weight.
In the context of the previous studies showing differential results for obese compared to normal weight women, Ewertz and colleagues suggest that letrozole may be more active as a hormonal therapy compared to anastrozole, resulting in more efficient estrogen suppression.