Obesity Raises Mortality in Young ER+ Breast Cancer Patients

An analysis of 80,000 women with early-stage breast cancer shows that obesity raises the risk of dying from breast cancer for pre-menopausal women diagnosed with estrogen receptor (ER)-positive disease. Obesity, defined as a body mass index of at least 30 kg/m², had a minimal effect on patients with ER-negative or post-menopausal ER-positive breast cancer.

The 20,000 younger women with early-stage breast cancer included in this study had a 34% higher likelihood of breast cancer-related death compared with the other breast cancer patients in the study, according to study author Hongchao Pan, of the Clinical Trial Service Unit at the University of Oxford in the United Kingdom. Pan presented the results of this 70-clinical trial analysis at a press conference in advance of the annual meeting of the American Society of Clinical Oncology (ASCO). These results will also be presented at the annual meeting, which will take place in Chicago from May 30–June 3.

The analysis was part of the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) study.

In the analysis, the 10-year breast cancer mortality for pre-menopausal women with ER-positive disease was 21.5% for obese women compared with 16.6% for non-obese women.

After adjustment for nodal status and tumor size, the 40,000 women with post-menopausal ER-positive disease had a 6% increase in risk of dying from their breast cancer if they were obese. Among women with ER-positive disease, regardless of menopausal status, obesity was important up to about the age of 55 years. The difference in the effect of obesity between pre- and post-menopausal ER-positive breast cancer patients was highly significant.

“This is the opposite of what we expected,” said Pan during the press conference. “We expected a bigger effect in post-menopausal women, but instead we saw a bigger effect in pre-menopausal women.”

No increase in risk was found among women with ER-negative disease.

This current study only addressed the impact of obesity on an existing breast cancer diagnosis and outcome and not the impact of obesity on the risk of being diagnosed with breast cancer.

“This is something that we will continue to watch, and of course, we will have to look at this in the context of other causes of mortality for people who are overweight as well as to look at results of other data sources,” said Peter P. Yu, MD, ASCO president-elect and director of cancer research at the Palo Alto Medical Foundation in California, who moderated the session but was not involved in the study.

“The bottom line is that obesity remains a negative prognostic feature, ” said Yu, “and something that we will need to address at a societal level.”