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.”

The mission of the American Association for Cancer Research is to prevent and cure cancer. Founded in 1907, AACR is the world’s oldest and largest professional organization dedicated to advancing cancer research. The membership includes nearly 27,000 basic, translational, and clinical researchers; health care professionals; and cancer survivors and advocates in the United States and more than 70 other countries. AACR marshals the full spectrum of expertise from the cancer community to accelerate progress in the prevention, diagnosis and treatment of cancer through high-quality scientific and educational programs. It funds innovative, meritorious research grants. The AACR Annual Meeting attracts more than 17,000 participants who share the latest discoveries and developments in the field. Special Conferences throughout the year present novel data across a wide variety of topics in cancer research, treatment, and patient care. AACR publishes five major peer-reviewed journals: Cancer Research; Clinical Cancer Research; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Epidemiology, Biomarkers & Prevention. Its most recent publication and its sixth major journal, Cancer Prevention Research, is the only journal worldwide dedicated exclusively to cancer prevention, from preclinical research to clinical trials. The AACR also publishes CR, a magazine for cancer survivors, patient advocates, their families, physicians, and scientists. CR provides a forum for sharing essential, evidence-based information and perspectives on progress in cancer research, survivorship, and advocacy.

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