High Insulin-Like Hormone Linked to Risk of Prostate Cancer

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Oct. 7 (Bloomberg) -- Higher than normal levels of an insulin-like hormone in the blood may signal an increased risk of prostate cancer, according to a new analysis of 12 studies.

The findings give doctors a possible target, the hormone called insulin growth factor or IGF-I, to stop prostate cancer, one of the most common malignancies in men. IGF-I is a protein in blood responsible for cell growth in adults, said the lead researcher, Andrew Roddam of the University of Oxford in England. This may cause cancerous tumors in the prostate to grow.

The risk for developing prostate cancer rose by 38 percent in men with high-normal levels of the hormone compared with those in the low-normal range, Roddam said. The analysis drew from multiple studies done in several countries. It appears in today's issue of the Annals of Internal Medicine.

``Knowledge that IGF-I is clearly associated with prostate cancer risk will be a step forward for those developing drugs which target the IGF-I receptor, a number of which are currently in clinical trials,'' Roddam said in a telephone interview.

Prostate cancer usually strikes men later in life. The walnut-sized prostate gland is part of the male reproductive system. About 186,320 new cases will be diagnosed this year in the U.S. and 28,660 men will die from it, according to the American Cancer Society. Doctors have identified only a few factors that raise risk for the disease including age, race and family history, the researchers said.

Lowering Hormone Level

Future studies could also examine whether changing a man's diet and lifestyle would lessen levels of IGF-I, Roddam said.

``There has been some suggestion that IGF-I levels are related to lifestyle and dietary factors,'' said Roddam, a statistical epidemiologist at the University of Oxford in England, in an Oct. 3 e-mail. ``These relationships need further work to understand them better. We are currently planning a program of work looking at the influences of diet and lifestyle on IGF-I levels.''

Researchers in the study analyzed data from 12 trials done in the U.S., Europe and Australia that included a total of 3,700 men with prostate cancer and 5,200 control patients without. All the men in the studies had their blood drawn. Those that developed prostate cancer received their diagnosis five years after their blood was taken, according to the study.

The analysis showed men in the highest quintile for IGF-I levels were 38 percent more likely to get prostate cancer than men with the lowest quintile for the hormone levels.

Risk Increase Consistent

The increased risk was consistent in both young and old men, men who were normal weight and overweight and regardless of whether they smoked or consumed alcohol or not, the study showed. The only possible difference in risk seen was according to how aggressive the cancer cells were, Roddam said. The association between IGF-I and prostate cancer risk was stronger in men who developed slow-growing cancer than those who had a more aggressive form of the disease, according to the article. Those findings, Roddam said, may just be due to chance.

Because all of the hormone levels seen in men who developed cancer were still in what's considered a normal range before their diagnosis, testing those levels isn't an effective screening tool for prostate cancer, Roddam said. Current screening techniques using the prostate-specific antigen test, or PSA, are ``more powerful,'' he said.