More breast cancer diagnosed in women with diabetes

Women with recently diagnosed diabetes may be more likely to also get a breast cancer diagnosis than those without diabetes, suggests a new study from Canada.

It's not the first time diabetes has been linked to new cases of breast or other cancers. But the findings also hint that at least part of the reason why doctors find more breast cancer in diabetics is because they're looking harder - and not necessarily because diabetes itself raises a woman's cancer risk.

"The relationship that we see (between diabetes and cancer), we wondered if it was something about the fact that people with diabetes go to the doctor's office more often," said Jeffrey Johnson, from the University of Alberta in Edmonton, who worked on the study.

"When a new diagnosis of diabetes is made, people undergo a lot of tests and general health exams." That may include breast cancer screening with mammograms, he added.

Previous studies found that people with diabetes have a higher risk of colorectal, liver and pancreatic cancers, along with breast cancer.

Researchers then suggested that certain behaviors might increase the risk of both types of diseases, including smoking, being sedentary and not eating well, and that those would explain the link.

Diabetes mellitus and breast cancer. Type 2 diabetes is a serious health problem that affects more than 7% of adults in developed countries. Up to 16% of patients with breast cancer have diabetes, and two major risk factors for type 2 diabetes-old age and obesity-are also associated with breast cancer. Three mechanisms have been postulated to associate diabetes with breast cancer: activation of the insulin pathway, activation of the insulin-like-growth-factor pathway, and regulation of endogenous sex hormones. Comparative cohort studies and case-control studies suggest that type 2 diabetes may be associated with 10-20% excess relative risk of breast cancer. Gestational diabetes mellitus, but not type 1 diabetes, might also be associated with excess risk of breast cancer. Moreover, diabetes and its complications can adversely affect cancer therapy and the use of screening, which will thus affect the outcome of patients with breast cancer.

###

Wolf I, Sadetzki S, Catane R, Karasik A, Kaufman B.

Institute of Oncology, Chaim Sheba Medical Center, Tel-Hashomer, Israel. wolfi@cshs.org

It's also possible that changes in insulin and blood sugar levels that come with diabetes make it easier for breast tumors to grow, Johnson said.

While those explanations could still be partly behind the increase in breast cancer researchers have noticed, extra doctor's visits and tests "certainly seems to contribute to some extent."

Johnson and his colleagues consulted a database including about 170,000 women in British Columbia - half with a recent type 2 diabetes diagnosis and half without diabetes - and tracked them for the following four to five years. During that time, about 2,400 women, or 1.4 percent, were diagnosed with breast cancer.