For many male baby boomers, the fates of rock star Frank Zappa and '60s guru Timothy Leary warned of a dangerous killer: prostate cancer, the most common cancer to strike nonsmoking men. Now researchers suggest a new way to spot those at high risk for this disease. They report in tomorrow's issue of Science that a protein called insulin-like growth factor-I (IGF-I) may serve as an early sign of prostate cancer risk, much as cholesterol serves as a heads-up for heart disease.
Many aging baby boomers are familiar with the blood test for prostate specific antigen (PSA); high levels are a sign that cancer may already lurk in their prostates. But mass-screening of PSA is not cost-effective. And because many prostate cancers don't advance to life-threatening disease even if left untreated, the test probably leads to many unnecessary surgeries.
Seeking a new angle on resolving these dilemmas, senior author Michael Pollak, a clinical oncologist at McGill University, turned to IGF-I, which stimulates the growth of prostate cells. The team studied nearly 15,000 men enrolled in the Physicians' Health Study at Harvard, who gave blood samples in 1982. Ten years later, 520 had been diagnosed with prostate cancer. When Harvard graduate student June Chan compared the 1982 IGF-I levels of 152 of these men to age-matched controls, she found that the 25% who fell at the high end of the IGF-I range were 4.3 times more likely to have developed prostate cancer than were the men at the low end.
"Of all the associations [with prostate cancer] we have looked at, this is one of the strongest," says Ann Hsing, an epidemiologist who studies prostate cancer at the National Cancer Institute. And in most cases it appears that the men didn't have cancer in 1982. That means "IGF is telling you something before the disease occurs," says team member Edward Giovannucci of Harvard. An IGF-I test might be used to identify high-risk men who need close monitoring or to recognize potentially aggressive tumors while they're still small.