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Breast cancer survivors more likely to develop diabetes

February 2013

Chemotherapy accelerates onset – better diabetes screening needed for all survivors

Women who have survived breast cancer are more likely to develop diabetes that women who have not had breast cancer, according to researchers at Women’s College Research Institute (WCRI) and the Institute for Clinical Evaluative Sciences (ICES).

“We found that the risk of diabetes among breast cancer survivors compared to women without breast cancer began to increase two years after diagnosis, with a 7 per cent increased risk that rose to 21 per cent after 10 years,” says Dr. Lorraine Lipcombe, study lead, scientist at Women’s College Research Institute and director of the Centre for Integrated Diabetes Care at Women’s College Hospital.

Lipscombe’s past research has already shown that women with diabetes have higher risk of postmenopausal breast cancer. Her latest study exploring the link between diabetes and breast cancer demonstrates that the trend goes both ways. The population-based study examined the incidence of diabetes among women in Ontario aged 55 years or older with breast cancer from 1996 to 2008 to that of age-matched women without breast cancer. Published in Diabetologia, it is the largest study so far to explore this relationship.

Onset of diabetes related to chemotherapy

Not only did the researchers find that breast cancer can increase the risk of diabetes, but the patterns of disease onset differed in patients who had undergone chemotherapy.

“The findings suggest that chemotherapy treatment may bring out diabetes earlier in susceptible women,” says Lipscombe, who is also an assistant professor of Medicine at the University of Toronto.

“We found that in women who received adjuvant chemotherapy, the onset of diabetes tended to happen much sooner.”

For these women (4,404 patients), the risk of developing diabetes was highest in the first two years after diagnosis (a 24 per cent increased risk compared with controls), but declined to 8 per cent increased risk after 10 years.

Lipscombe says that researchers are still unsure of the exact nature of the relationships between these diseases.

“Insulin resistance is a common risk factor in both diabetes and breast cancer, and this may partially explain why these diseases are related,” she says.

Chemotherapy patients are commonly prescribed glucocorticoid drugs to treat nausea. These drugs can trigger weight gain and contribute to blood sugar imbalances that may increase the risk of developing diabetes in women who are predisposed.

“The effects of glucocorticoids are known to wear off over time,” says Lipscombe. “This could explain why, in women who’ve had chemotherapy, we found that the risk of diabetes was highest in the year or two immediately following their treatment.”

“These findings support a need for closer monitoring of diabetes among breast cancer survivors,” she says.

This study was made possible with data provided by the Institute for Clinical Evaluative Sciences (ICES) and Cancer Care Ontario (CCO) and through funding support to ICES from an annual grant by the Ministry of Health and Long-Term Care (MOHLTC). Funding was provided by CCO and the Ontario Institute for Cancer Research (through funding provided by the MOHLTC and the Ministry of Research and Innovation of the Government of Ontario) and a Canadian Diabetes Association/Canadian Institutes of Health Research (CIHR) Clinician Scientist Award.

View Diabetologia article

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