No one should be surprised that the more sexual partners a man has, the greater his risk of contracting HIV, not to mention syphilis, gonorrhea and other venereal diseases. According to a new study, however, there may be a surprise addition to this list — prostate cancer.

The authors of the study, professor Karin Rosenblatt of the University of Illinois, and Janet Stanford and Kristine Wicklund of Seattle's Fred Hutchinson Cancer Research Center, claim to have found "a direct relationship between the number of lifetime female sexual partners and the risk of prostate cancer in middle-aged men."

..."while many studies have examined the cancer risk of sexual factors such as age at first intercourse, number of sexual partners and exposure to sexually transmitted diseases"...

Published in the June 15 issue of the American Journal of Epidemiology, the study was based on a survey of 1,456 men ages 40-64 in King County, Washington. The study group consisted of 753 men who had been diagnosed with prostate cancer between 1993 and 1996. The control group of 703 men was chosen at random and had an age distribution similar to that of the study group.

Analysis of the survey showed a strong relationship between risk and number of female sexual partners, with those who reported 30 or more sexual partners having more than twice the risk of getting prostate cancer. They found no relationship between prostate cancer and the frequency of intercourse.

Asked for his take on the study, TheDoctor's expert in this field, Dr. Robert G. Lerner, Professor of Medicine at New York Medical College, said that "while many studies have examined the cancer risk of sexual factors such as age at first intercourse, number of sexual partners and exposure to sexually transmitted diseases, the amount of risk associated with these turns out to be small, compared to the well known risk factors of age, race and differences between countries."

Dr. Lerner also pointed out that "there are several possible interpretations of the results of this latest study. One is that there could be an undetected infectious cause of the increased risk; another is that increased sexual activity might not be a risk factor in itself, but may be simply a marker of high testosterone levels, which are a known risk factor for prostate cancer."

Professor Rosenblatt also counseled that although the data from her study were a definite cause for concern, they should not be overplayed. "I'm not sure we've figured out the mechanism with this," she said, "and also some studies don't show any association and some studies do, so I think there needs to be a little more research in this area."

Reviewed by Robert G. Lerner, M.D.