Prostate cancer is one of the most common cancers in men, affecting about 160 per 100,000 every year and killing 26. While doctors can screen for it, many prefer not to do so because most tumors grow slowly and never cause any harm.
The researchers tracked more than 22,000 Californian men who had been evaluated for infertility between 1967 and 1998.
Over the decade following the evaluation, 1.2 percent of the infertile men developed prostate cancer, compared to only 0.4 percent of the fertile men. Both of those figures are higher than would be expected in the general population, possibly because these men are more likely to visit health-care professionals and get diagnosed.
After accounting for age, infertility increased the chances of being diagnosed with aggressive tumors 2.6 times. For slow-growing cancers, the risk climbed 1.6 times, the authors report in the journal Cancer.
"The absolute risk of men developing prostate cancer is still very small," said Dr. Thomas Walsh of the University of Washington, who led the research. "What is surprising is that we see this high rate of high-grade prostate cancer."
He said the specific effect on aggressive tumors was important for two reasons. First, it means the increased risk is not just a result of infertile men being screened more often because of their visits to the urologist. Had that been the case, researchers would expect to see the same increase in slow-growing cancers.
Second, infertility might point to more lethal cancers, singling out men who should give an extra thought to screening.
It is not yet clear what could account for the link between infertility and prostate cancer. But researchers speculate that damages to the male sex chromosome -- for instance through exposure to environmental toxins in the womb -- may be involved.
Other risk factors for prostate cancer include older age, being African American, family history and obesity.
The American Urological Association - of which Walsh is a member -- recommends screening for men aged 40 or older. However, Walsh said he did not believe that all young men with fertility problems should be screened.
Still, he said that if the findings are confirmed, doctors might consider lowering the screening threshold when seeing infertile patients.
Dr. Otis Brawley, chief medical officer of the American Cancer Society, agreed. The Cancer Society recommends that doctors discuss the pros and cons of screening with patients at age 50.
"A man who has infertility problems should take (the new findings) into consideration when thinking about prostate cancer screening," Brawley, who was not involved in the study, told Reuters Health.
The treatments for prostate cancer -- surgery or radiation -- may lead to incontinence and erectile dysfunction in about a third of patients.
"We treat a lot of prostate cancers that don't need to be treated," said Brawley. "We desperately need studies that will point to markers of aggressiveness."
SOURCE: Cancer, online March 22, 2010.