Breast cancer patients are nearly 50 percent more likely to die of any cause if they also have diabetes, according to a comprehensive review of research conducted by Johns Hopkins physicians.
The findings, published in the January issue of the Journal of Clinical Oncology, suggest future research could focus on whether high levels of insulin in patients with type 2 diabetes could play a role in promoting tumor growth.
The researchers who conducted the review also found that diabetics tend to be diagnosed with later-stage breast cancers and to receive altered, potentially less effective treatment regimens.
"When patients are faced with a diagnosis of breast cancer, which they see as an imminent threat to their lives, diabetes care often goes on the back burner," says study leader Kimberly S. Peairs, M.D., an assistant professor of medicine at the Johns Hopkins University School of Medicine. "This research suggests we may need to proactively treat the diabetes as well as the cancer," she adds, noting that diabetes is a systemic disease that has many different effects on the body.
Peairs and her team conducted a systematic review and meta-analysis of previously published research on breast cancer and diabetes, ultimately looking in depth at eight studies. In six of seven studies of breast cancer patients, preexisting diabetes was associated with significantly higher long-term, all-cause mortality.
Diabetes and cancer are major causes of illness and death worldwide. In 2007, in the United States alone, roughly 24 million people had diabetes (about 8 percent of the population) and 2.5 million were survivors of breast cancer. Diabetics are known to have a higher risk of breast cancer, Peairs says.
Peairs says her research suggests that diabetics diagnosed with breast cancer may get less effective treatment because practitioners may be concerned about these patients suffering more side effects from chemotherapy or radiation treatments as a result of the metabolic condition. Patients also may be more likely to be hospitalized, get infections, and/or become anemic — complicating their care. Peairs says the higher death rate may also be linked to the fact that they come to breast cancer treatment less healthy than their counterparts without diabetes, which is associated with obesity, high cholesterol and high blood pressure.
Women with diabetes may also be at greater risk of chemotherapy-related toxicity, which may explain — and even justify — some of the less aggressive treatment, she says.
Peairs says more research should reveal whether increased insulin production in type 2 (adult onset) diabetics contributes to worse outcomes among diabetic breast cancer patients. Small studies suggest that some diabetes drugs may be associated with worse outcomes for cancer patients while other medications may actually improve survival.
She noted that the popular drug metformin, which makes diabetes patients more insulin-sensitive thereby lowering the amount of unused insulin in the body, may be associated with better survival outcomes.
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