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Breast cancer survivors may be more likely to develop diabetes

Dec, 13, 2012

By Patricia Nicholson

New research from Women’s College Research Institute and the Institute for Clinical Evaluative Sciences indicates that post-menopausal breast cancer survivors have an increased risk of developing diabetes compared to women who haven’t had breast cancer.

These research findings build on what is already known about a relationship between breast cancer and diabetes.

“There’s increasing evidence showing that patients with diabetes have a higher risk of several types of cancer, and worse prognoses when they get it compared to those without diabetes,” says Dr. Lorraine Lipscombe, a scientist at Women’s College Research Institute and lead author of the study. “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.”

The results showed a small but significant increase in diabetes risk among post-menopausal breast cancer survivors.

Dr. Lipscombe and her colleagues used health databases from Ontario to identify 24,976 post-menopausal survivors of early stage breast cancer diagnosed between 1996 and 2006, and 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.

During 12 years of followup, 14,576 women were diagnosed with diabetes: 2,440 cases in breast cancer survivors and 12,136 in the comparison group. The researchers found that the breast cancer survivors were more likely to develop diabetes than the comparison group. The risk was 7 per cent higher in breast cancer survivors two years after diagnosis, but increased over time to 21 per cent higher 10 years after diagnosis.

“Among postmenopausal breast cancer survivors we found that compared to age-matched women who didn’t have breast cancer, they had a small but significant increase in developing diabetes over time, and the risks started to go up in the majority of women after two years from their cancer diagnosis,” Dr. Lipscombe says. “But we also found that among the women who got chemotherapy the risk actually increased early on after their diagnosis.”

There was a different pattern among breast cancer survivors who underwent chemotherapy. In this group, the diabetes risk was concentrated in the first two years after diagnosis, with a 24 per cent higher risk of diabetes among breast cancer chemotherapy patients compared to the comparison group. There was no increased risk after that two-year period in women who had chemotherapy.

“We don’t know why that is but we wonder if something about the chemotherapy might have unmasked or brought out diabetes in women who were vulnerable to getting it, and brought it out at that stage instead of later,” Dr. Lipscombe says. “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 notes that the study cannot determine the reasons for the relationship between breast cancer and diabetes, but says one possibility is that there are shared risk factors between the two conditions, such as obesity and insulin resistance, and this may lead to a common risk for both breast cancer and diabetes.

“This study raises awareness of an association between cancer and diabetes that warrants further research,” says Dr. Lipscombe, adding that the results also suggest that as breast cancer patients are surviving more long-term, there is a need to pay more attention to some of the long-term health consequences that may affect these women.

“Further work needs to be done to understand what those consequences are, but in the mean time one potential issue for them is an ongoing increased risk of diabetes, and so 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. “We also need to understand what are some of the other risk factors for that population that may put them at higher risk, and so they need to speak to their doctors about what their risk factors might be and whether they should be screened more closely for diabetes.

The study was published in the journal Diabetologia on Dec. 12, 2012.

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  • Women's College Hospital