CVD Plus Excess Weight Increases Breast Cancer Risk

Excess body weight is a well-known risk factor for breast cancer in postmenopausal women, but is the risk the same in women who also have cardiovascular disease (CVD) or type 2 diabetes?

The short answer is no for CVD and yes for type 2 diabetes, a recent analysis suggested.

Women with excess body weight who developed CVD had a significantly higher risk for breast cancer, according to the study, published earlier this month in Cancer. The researchers, led by Heinz Freisling, PhD, reported that each 5 kg/m² increase in BMI was associated with a 31% higher risk for breast cancer in women who developed CVD vs a 13% higher risk in women without CVD.

However, women with excess body weight who developed type 2 diabetes did not have a higher risk for breast cancer than women who did not develop diabetes.

These findings indicate that “weight control/prevention measures are particularly important for women with a history of CVD,” explained Freisling, with the Nutrition and Metabolism Branch, International Agency for Research on Cancer, part of the World Health Organization.

Research on how cardiometabolic diseases, such as CVD and type 2 diabetes, affect the association between adiposity and breast cancer risk in postmenopausal women is limited. 

Earlier work by the team had found an additive interaction between obesity and CVD and overall cancer risk as well as obesity-related cancer risk but no such additive interaction between obesity and type 2 diabetes with cancer risk. However, the research did not address whether CVD or type 2 diabetes modified the relationship between body weight and breast cancer risk, the researchers noted. 

In the current analysis, Freisling and colleagues analyzed individual participant data from the European Prospective Investigation into Cancer and Nutrition and UK Biobank on 168,547 postmenopausal women who did not have cancer, type 2 diabetes, or CVD at the outset.

After a median follow-up of nearly 11 years in both cohorts, 6793 postmenopausal women developed breast cancer.

Pooled data from both cohorts revealed that, with BMI increases of 5 kg/m², women who developed CVD had a higher risk for breast cancer (hazard ratio [HR], 1.31) than those who did not develop CVD (HR, 1.13). The combination of overweight (BMI ≥ 25) and CVD was estimated to lead to 1.53 more cases of breast cancer per 1000 people per year than expected.

However, type 2 diabetes did not modify the relationship between adiposity and breast cancer risk.

What might explain the different associations?

“We know from animal studies that CVD can lead to cancer growth through biological pathways that are not shared with adiposity. For example, a stressed heart muscle releases proteins into the blood stream that can trigger cancer growth,” Freisling said.

However, “we know from other studies that excess adiposity and diabetes affect breast cancer risk through similar biological pathways,” which “may result in the same increase in cancer risk,” Freisling said.

Overall, these findings could inform risk-stratified breast cancer screening programs, Freisling and colleagues noted. But it’s unclear how weight loss in women with and without CVD would affect their breast cancer risk. “This should be investigated in future studies,” Freisling said.

Stephanie Bernik, MD, who was not involved in the research, said the findings are “interesting” but cautioned against drawing any firm conclusions from the study.

“I think the bottom line is we need to look into it a little more deeply and uncover the mechanism for the association,” said Bernik, chief of the breast service at Mount Sinai West and associate professor of surgery, Icahn School of Medicine at Mount Sinai, New York City. “For now, perhaps physicians could be more aware that if someone has obesity and cardiovascular disease, they may be at higher risk for breast cancer.”

The study had no commercial funding. Freisling and Bernik had no conflicts of interest.