A possible link between men who have had vasectomies and the subsequent development of prostate cancer has been suggested in two separate studies published in the December issue of the American Journal of Epidemiology. But in the same issue, an adjunct associate professor of epidemiology and biostatistics at the University of North Carolina warns in an accompanying commentary that the findings are "far too preliminary to warrant any change in medical practice."

Vasectomy, a relatively simple form of male sterilization in which the tube that carries sperm to the penis is cut, has become an increasingly popular method of birth control. About 455,000 procedures are performed in clinics and doctors' offices annually.

Prostate cancer, which strikes one in 11 men, is the leading cancer among men and the third leading cause of cancer death; about 106,000 cases are diagnosed each year and about 30,000 deaths are recorded annually.

The link between vasectomy and prostate cancer was an unexpected finding in the first study, according to its lead author Lynn Rosenberg, assistant director of the Slone Epidemiology Unit at the Boston University School of Medicine. The group observed the association in a comparison of 220 newly diagnosed prostate cancer patients, 571 men who did not have cancer and 960 who had other malignancies between 1976 and 1988. The researchers were looking for links between various diseases and risk factors, but not specifically those related to prostate cancer.

The second study, directed by Curtis Mettlin, an epidemiologist at the Roswell Park Cancer Institute in Buffalo, was designed to test the possibility that vasectomy was a risk factor for prostate cancer. He compared 614 men with prostate cancer who were hospitalized at Roswell Park between 1982 and 1988 with 2,588 control patients who had other cancers. Mettlin found twice the risk of prostate cancer among those who had undergone vasectomies.

Population studies such as these are "provocative" and should be followed by larger studies and biological research before any final conclusions are drawn, epidemiologist Harry A. Guess said in his commentary.