Breast cancer survivors may be more likely to develop diabetes

Post-menopausal breast cancer survivors may have an increased risk of developing diabetes compared to women who haven’t had breast cancer, a study shows.

Researchers already knew that there is a relationship between breast cancer and diabetes: women with diabetes appear to have a higher risk of developing several types of breast cancer.

“This study was to see whether the reverse was true: whether cancer patients might have a higher risk of future diabetes once they survive their cancer,” says Dr. Lorraine Lipscombe, a scientist at Women’s College Research Institute (WCRI) and lead author of the study.

Rising risks

The study showed an increase in diabetes risk among post-menopausal breast cancer survivors, compared to women without breast cancer. This increased risk became stronger over time:

• Two years after their cancer diagnosis, breast cancer survivors had a seven per cent higher risk of diabetes
• 10 years after their cancer diagnosis, breast cancer survivors has a 21 per cent higher risk of diabetes

However, there was a different pattern among breast cancer survivors who had undergone chemotherapy. In this group, the diabetes risk was concentrated in the first two years after diagnosis, with a 24 per cent higher risk compared to the non-cancer group. After that, there was no increased risk in women who had chemotherapy.

The researchers aren’t sure why the pattern is different in women with chemotherapy. It could be that some aspect of chemotherapy triggers diabetes earlier in women who are vulnerable to it.

“One possibility is, we know that in most cases when a patient gets chemotherapy they get medications called glucocorticoids, or steroids, which we know increase propensity for diabetes,” Dr. Lipscombe says.

Long-term health issues

Because breast cancer patients are now surviving for much longer periods of time, Dr. Lipscombe notes that we need to pay more attention to some of the long-term health issues that may affect these women. One of those issues is an increased risk of diabetes.

“Greater attention to preventive measures such as healthy lifestyle, regular exercise and keeping to a healthy weight might help to mitigate that risk,” Dr. Lipscombe says.

She adds that breast cancer survivors may need to speak to their doctors about other risk factors they may have for diabetes, and whether they should be screened more closely for the condition.

How the study was done

Dr. Lipscombe and her colleagues at WCRI and the Institute for Clinical Evaluative Sciences used health databases from Ontario to identify 24,976 post-menopausal survivors of early-stage breast cancer who were diagnosed between 1996 and 2006. The researchers also identified a comparison group of 124,880 women the same age who did not have breast cancer. None of the women had diabetes at the start of the study.

The study followed both groups for 12 years. During that time, 14,576 women were diagnosed with diabetes: 2,440 cases in breast cancer survivors and 12,136 in the comparison group.

The study was published in the medical journal Diabetologia.