Breast cancer and diabetes: New study finds stronger link

December 12, 2012 | by Roberta Nichols

The association between diabetes and cancer is growing stronger. Researchers have now found that breast cancer survivors are at increased risk for developing diabetes.

Already, women with diabetes have been found to have an estimated 20 percent higher risk of post-menopausal breast cancer. The new findings – published in Diabetologia, the journal of the European Association for the Study of Diabetes – is among the first to establish post-menopausal breast cancer survivors’ risk of, in turn, developing diabetes.

In this study, researchers followed the cases of women age 55 and older in Ontario, Canada, from 1996 to 2008. They compared data from 24,976 post-menopausal women with newly diagnosed breast cancer with data from 124,880 post-menopausal women without breast cancer.

Post-menopausal breast cancer survivors may find themselves having to check their blood glucose several times a day. New research shows they're at an increased risk of diabetes. Post-menopausal breast cancer survivors may find themselves having to check their blood glucose several times a day. New research shows they're at an increased risk of diabetes.

Researchers found that the risk of diabetes among breast cancer survivors began to increase two years after diagnosis.  The highest risk was in the first two years in those who received adjuvant therapy such as chemotherapy and radiation.

“Our study suggests that greater diabetes screening and prevention strategies among breast cancer survivors may be warranted,” the researchers wrote.

Joanne Mortimer, M.D., director of the Women’s Cancers Program at City of Hope,  says increased monitoring is crucial for breast cancer patients.

“Treatment for early stage breast cancer results in long-term complications, including diabetes,” said Mortimer, who was not involved in the new study. “The problem is to sort out why.”

One reason breast cancer patients might be more prone to diabetes could be weight gain, said Mortimer, pointing out that women on treatment generally add pounds.  This could be caused by going into menopause or from anti-nausea drugs (“glucocorticoids”), which can make blood sugar soar.

Weight gain also could be caused by endocrine therapy, such as the aromatase inhibitors that halt  tumors’ growth by stopping certain hormones from turning into estrogen. “So there are a million reasons why these folks could become diabetic,” Mortimer said. “Recognizing the problem is critical if we are ever going to sort out the causes.”

The study reinforces the need for continued medical surveillance of patients, she said.  “It is important that women are followed longitudinally to work out what components of their treatment precede the development of diabetes.”

As for what’s most likely to cause breast cancer survivors to get diabetes?

“My bet is on the hormones, either putting young women into menopause and/or aromatase inhibitor hormones which are known to cause weight gain ... which, of course, increases the risk of diabetes,” said Mortimer.

For more information about diabetes and breast cancer, visit City of Hope's programs online.

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