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Obesity does not increase a woman's risk of death from early breast cancer, according to a new study.
"At the moment, obesity alone is not a factor that should guide adjuvant treatment decisions," said Dr Ivana Sestak, a breast cancer epidemiologist at Queen Mary, University of London. "Much stronger factors," such as nodal status and tumour size and grade, far outweigh the effect of obesity in terms of clinical practice, she said.
Dr Sestak was not involved with the new study, which was published online in the Journal of Clinical Oncology.
The analysis used data on participants in the phase III BIG 1-98 trial, which compared tamoxifen with letrozole among 4 760 postmenopausal women with endocrine-responsive early invasive breast cancer. Women in the trial were treated for five years and followed for a median of 8.7 years.
How the study was done
The authors of the current report, led by Dr Marianne Ewertz at the University of Southern Denmark, stratified patients by BMI at randomisation: 40% were normal weight (BMI <25 kg/m2), 36% were overweight (BMI 25 to <30 kg/m2), and 23% were obese (BMI at least 30 kg/m2).
Overall survival was not significantly worse for obese or overweight patients compared to normal weight patients, although there was a nonsignificant trend toward poorer survival in the obese group.
The investigators also compared overall survival among patients in each treatment arm and found that BMI did not affect the relative efficacy of either tamoxifen or letrozole. For example, overall survival was similar for all women on letrozole, regardless of BMI.
Incomplete oestrogen suppression has been suggested as a driver of worse outcomes among obese women on anastrozole, a similar drug in the class of aromatise inhibitors.
"Overweight and obese women have a poorer outcome than normal weight women, but the exact reasons behind this are very complex, and at least in part related to higher oestrogen levels," Dr Sestak said. "We need to understand better if overweight and obese women really need higher doses of an aromatise inhibitor for complete oestrogen suppression or if only specific aromatise inhibitors are capable of doing so."
Dr Marianne Ewertz, the study's lead author, did not reply to an email from Reuters Health requesting comment on the study.
(Reuters Health, October 2012)
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