Does Breast Cancer Increase Diabetes Risks?

Breast cancer survivors appear to be at higher risk of diabetes

December 12, 2012 / Author:  / Reviewed by: Joseph V. Madia, MD

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(dailyRx News) Scientists have found that diabetes and cancer like to interact. A new study suggests women who’ve had breast cancer and their doctors need to be aware that developing diabetes is a real risk.

Post-menopausal women who’ve been treated for breast cancer are more likely to develop diabetes than women who haven’t had the disease. This increased risk for diabetes in women who received chemotherapy starts to decline after two years.

This study suggests former breast cancer patients need to be monitored for diabetes more closely.

"Ask your doctor about diabetes screening"

Lorraine Lipscombe, MD, Msc of Women's College Hospital and the Women's College Research Institute in Toronto, Canada, led the study to look at links between breast cancer and diabetes in postmenopausal women. This is one of the first such investigations.

Researchers used population data from Ontario, Canada to compare rates of diabetes among women 55 and older who had and those who never had breast cancer. They further analyzed the association among women who had received chemotherapy. Almost 25,000 of the study members had been diagnosed with and treated for breast cancer. These women were compared with about 125,000 women who had not had breast cancer. The women were followed for just under 6 years.

Among the entire group, 9.7 percent of the women developed diabetes. Risk factors among breast cancer survivors depended on types of therapy they’d received and how far out they were from diagnosis.

Compared to women without breast cancer, researchers found that women with breast cancer saw diabetes risks steadily increase starting two years after diagnosis – going from 7 percent increased risk to a 21 percent increased risk 10 years later.

Interestingly, just the opposite occurred in women who had received chemotherapy. Their risks were highest in the first two years following diagnosis and steadily declined over time, decreasing from 24 percent increased risk to 8 percent increased risk after 10 years.

dailyRx News asked breast cancer specialist, Adam Brufsky, MD, PhD of the University of Pittsburgh about this. He told us he doesn’t see more diabetes in his breast cancer patients, but acknowledges the possible connection. “This seems entirely plausible and may be related to weight gain from menopause induced by some breast cancer treatments, including chemotherapy.”

Dr. Lipscombe agrees, “It is possible that chemotherapy treatment may bring out diabetes earlier in susceptible women. Increased weight gain has been noted in the setting for adjuvant [after primary treatment] chemotherapy for breast cancer, which may be a factor in the increased risk of diabetes in women receiving treatment.”

Researchers identified other risk factors. They said drugs taken during treatment could possibly be involved in the increased risk. Glucocorticoid drugs, which are given to help control nausea during chemo, may play a role. Blood sugar spikes are one of the side effects of these drugs, which are sold under a number of brand names.

The decline in diabetes among those who had chemo may be due to the fact that the disease was detected during treatment, so they were no longer followed. Glucocorticoid effects also decline over time, according to the study authors.

Researchers were puzzled as to why women who didn’t receive chemotherapy saw increasing risks. The two diseases may share risk factors, the researchers said.

"One such risk factor is insulin resistance, which predisposes to both diabetes and many types of cancer— initially, insulin resistance is associated with high insulin levels and there is evidence that high circulating insulin may increase the risk of cancer,” Dr. Lipscombe said in a press release.

She continued, “However, diabetes only occurs many years later when insulin levels start to decline—therefore it is possible that cancer risk occurs much earlier than diabetes in insulin-resistant individuals, when insulin levels are high."

The net result of these findings is a recommendation that women who have had breast cancer be monitored more closely for diabetes, the authors conclude.

This study was published December 12 in Diabetologia, the journal of the European Association for the Study of Diabetes. Funding for this study came from Cancer Care Ontario, Ontario and a Canadian Diabetes Association/Canadian Institute of Health Research (CIHR) Clinician Scientist Award. No conflicts of interest were reported.