Diabetes and obesity increase risk for breast cancer development

Researchers of the study, reported at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium, held Dec. 6-10, 2011, also looked at overall cancer incidence and discovered that use of one diabetes drug was associated with a lower rate of any cancer, while another was associated with an increased risk.

Researchers evaluated health care data from a region of 1.5 million people living in Southwestern Sweden to provide a comprehensive picture of cancer risk.

"We are looking at everybody, and we found that diabetes in adult women and obesity in women aged 60 and older significantly increased breast cancer risk," said Håkan Olsson, M.D., professor in the departments of oncology and cancer epidemiology at Lund University. "This is useful information for women who want to know their risk and who can take steps to lower it."

He and his colleagues examined records of 2,724 patients up to 10 years before they developed cancer and 20,542 patients who never developed the disease.

They found that obesity in women after age 60 increased risk for developing breast cancer by 55 percent. "At the most, 15 out of 100 obese women would get breast cancer compared with slightly less than 10 out of 100 in the general population," Olsson said.

Women with diabetes had a 37 percent increased risk for developing breast cancer if their diabetes had been diagnosed up to four years before cancer was diagnosed.

Women with abnormally low levels of blood lipids (mostly cholesterol) had a 25 percent greater risk for developing breast cancer, while high levels of blood lipids appeared to be associated with a lower risk for breast cancer. The mechanisms behind these effects are unclear, and the finding needs to be replicated in a different population-based study, Olsson said.

Researchers also looked at the national drug prescription registry to examine the link between risk for all cancers and use of two diabetes drugs, glargine and metformin. In this study, investigators found that glargine use, which had been associated with increased cancer development in previous European studies, almost doubled the risk for development of any cancer, while metformin was linked to an 8 percent lower risk for cancer in patients with diabetes.

Olsson said more research is needed to clarify the specific cancers at increased risk. The number of patients in this study who developed breast cancer using these medications was too small to make any link to breast cancer risk, specifically, he said.

Provided by American Association for Cancer Research