• Obesity
• Breast Cancer
• Oncology Clinical Trials

• Obesity
• Breast Cancer
• Oncology
• Oncology Clinical Trials

Obesity is a strongly associated with an increased risk of breast cancer-related mortality in premenopausal and perimenopausal women with early estrogen receptor-positive (ER+) breast cancer, regardless of treatment type, surgery type, tumor size, human epidermal growth factor 2 (HER2) status, or nodal status [Pan H et al. J Clin Oncol 2014]. On behalf of the Early Breast Cancer Trialists' Collaborative Group (EBCTCG), Dr Hongchao Pan, University of Oxford, Oxford, United Kingdom, presented data from an analysis of the effect of obesity on the prognosis of 80,000 women with early-stage breast cancer.

The study reported on data from 80,000 patients analyzed by the EBCTCG with early breast cancer who participated in a collective 70 trials and had data available on BMI, ER status, menopausal status, disease recurrence, and death. The analysis used Cox regression to determine the independent effect of obesity on mortality associated with breast cancer. Age, HER2 status, nodal status, disease grade, diameter of tumor, trial treatment, and surgery type were adjusted for in the analysis.

Obesity was found to have an appreciable adverse effect on mortality in the 20,000 premenopause and perimenopausal women with ER+ breast cancer. Among the patients, the rate of breast cancer mortality was 21.5% in obese patients (BMI ≥30 kg/m²) compared with 16.6% in women of normal weight (BMI, 20–25 kg/m²), resulting in a relative risk (RR) of 1.34 (95% CI, 1.22–1.47; p<0.00001; Figure 1). In addition, the risk of breast cancer mortality rose incrementally with increasing BMI. These effects of obesity were largely independent of the type of treatment the women were given. In contrast, obesity had little effect on mortality in the 40,000 postmenopausal women with ER+ breast cancer (RR, 1.06), and no apparent effect at all on mortality in the 20,000 women with ER-negative disease (RR, 1.00).

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Figure 1.

Effect of Obesity on Breast Cancer Mortality

BMI=body mass index; ER=estrogen receptor; RR=relative risk; 2p=2-sided p-value; SE=standard error. Reproduced with permission from H Pan, PhD.

Participants in these studies had lower rates of obesity than those seen in the general population, suggesting there may be some selection bias for trial participants.

Prof. Pan concluded that, for unexplained reasons, obesity is a strong, independent risk factor for mortality in premenopausal and perimenopausal women with early-stage ER+ breast cancer. The EBCTCG will publish these results collaboratively, after consultation about their interpretation with the hundreds of trialists from around the world who conducted the studies.

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