Obesity linked to mortality in premenopausal, ER-positive early breast cancer
Obesity was an independent risk factor for breast cancer mortality among premenopausal women with ER-positive disease, according to results of a meta-analysis.
Researchers did not observe the association among postmenopausal women with ER-positive disease, or in women with ER-negative disease.
“Obesity is reportedly associated with worse prognosis in early breast cancer, but this association could depend strongly on ER positivity and ovarian activity,” Hongchao Pan, PhD, lead study author and a researcher at the University of Oxford in the United Kingdom, said during a press conference. “Previously studies of this were inconclusive.”
Pan and colleagues evaluated Early Breast Cancer Trialists’ Collaborative Group data on 80,000 women enrolled in 70 trials. The researchers compared outcomes of women who had a normal weight (BMI range, 20 to 25), those who were overweight (BMI range, 25 to 30) and those who were obese (BMI ≥30) who received the same treatment in the same clinical trial.
Mean follow-up was 8 years.
In women with ER-positive disease (n=60,000), BMI was significantly associated with breast cancer mortality among those who were pre- and postmenopausal (P˂.00001 for both). However, when researchers controlled for tumor characteristics, obesity was only significantly associated with breast cancer mortality among the 20,000 women with ER-positive disease who were premenopausal (RR=1.34; 95% CI, 1.22-1.47).
Among 40,000 postmenopausal women with ER-positive disease, researchers observed a trend toward greater breast cancer mortality among those with BMI ≥30, but this association was not statistically significant (RR=1.06; 95% CI, 0.99-1.14).
Pan and colleagues reported little association between breast cancer mortality and BMI among the 20,000 women with ER-negative disease, and they observed no association after they controlled for tumor diameter and nodal status.
When researchers evaluated BMI in analyses controlled for age in place of menopausal status, obesity was associated with breast cancer mortality in women with ER-positive disease until age 55 years.
“Obesity substantially increases blood estrogen levels only in postmenopausal women, so we were surprised to find that obesity adversely impacted outcomes only in pre-menopausal women,” Pan said in a press release. “This means we don’t understand the main biological mechanisms by which obesity affects prognosis.”
For more information:
Pan H. Abstract #503. Scheduled for presentation at: 2014 ASCO Annual Meeting; May 30-June 3, 2014; Chicago.
Disclosure: The study was funded by the British Heart Foundation, Cancer Research UK and the UK Medical Research Counsel. The researchers report no relevant financial disclosures.