Association of C-peptide concentration with prostate cancer incidence in a prospective cohort

While studies have consistently shown that men with diabetes are at a decreased risk for prostate cancer, the reasons have been unclear. By evaluating prostate cancer data from a large, long-term cohort study, researchers at Johns Hopkins University have shown that those with high concentrations of C-peptide – a marker of high insulin secretion that is a hallmark of diabetes – had a measurable decrease in prostate cancer risk.

“Metabolic perturbations influence cancer risk, that much is becoming clear to us, and we are learning more about the fundamental issues in biology that guide prostate cancer development,” said Gabriel Lai, a doctoral student in the Department of Epidemiology at Johns Hopkins Bloomberg School of Public Health. “One interesting possibility is that, over time, diabetics generally have less testosterone in their bloodstream than non-diabetics, which might lower risk of prostate cancer.”

Lai and his colleagues used data from a large-scale study known as CLUE II, which had enrolled almost 23,000 adults in Washington County, Maryland in 1989. With funding from the National Cancer Institute, they examined the history of 264 men with confirmed prostate cancer and matched them with a group of 264 men without prostate cancer with a similar distribution of age and race.

For each participant, the researchers measured the amount of C-peptide in the blood they donated when they enrolled in the study. Researchers consider C-peptide to be a surrogate marker for insulin secretion because both molecules derive from the same precursor molecule, with insulin degrading faster than C-peptide. They found that patients that had elevated levels of C-peptide in their bloodstream when they started the study were about one-third less likely to develop prostate cancer later. This was true even among men without diabetes.

The researchers also report a markedly lower risk of non-metastasized prostate cancer. Men with higher C-peptide levels in their blood were half as likely to develop organ-confined prostate cancer, Lai says.

“Even though diabetes and obesity are often linked to different types of cancer, our findings illustrate the idea that the link between cancer and metabolic diseases is not the same for every variety of cancer,” Lai said. “Obviously, having high levels of insulin does not promote health but perhaps such disorders can provide insight into the mechanisms of prostate cancer to help us learn how to eventually prevent prostate cancer.”

Contact: Greg Lester
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American Association for Cancer Research