BETHESDA, Md--Physicians have long hypothesized that natural variation in sex hormones may influence prostate cancer risk, said Meir Stampfer, MD, of the Harvard School of Public Health. Efforts to prove this, however, have yielded unclear results. Now, by examining the interrelationship of different sex hormones, Dr. Stampfer and his colleagues have achieved what he calls the first clear demonstration that circulating levels of sex hormones can predict a man's risk of developing prostate cancer.
The finding further suggests the need for studies of how lifestyle practices might change circulating hormone levels, he said at the General Motors Cancer Research Foundation annual conference.
Previous studies failed to demonstrate a convincing link for a variety of reasons, Dr. Stampfer said. Some were simply too small. Often the blood used was collected after diagnosis of prostate cancer, and concern lingered that the cancer therapy or the cancer itself had altered sex hormone levels among the participants in the study.
Dr. Stampfer and his colleagues, who included Peter H. Gann, MD, ScD, turned to the Physicians' Health Study. In 1982, 14,916 of the 22,071 male US physicians in the study, all with no prior cancer, provided samples of their blood, which were frozen and stored. Study participants answered follow-up questionnaires every 6 months. The Harvard team matched 222 physicians who developed prostate cancer in the following decade with 390 healthy, cancer-free participants.
Blood from each man was thawed and measured for testosterone; DHT (dihy-drotestosterone, the active form of testosterone in the prostate); AAG (3-alpha-androstanediol glucuronide, an androgenic metabolite of testosterone); estradiol(Drug information on estradiol); prolactin; and SHBG (sex hormone binding globulin).
"Our thinking was that the androgens--testosterone, DHT, and AAG--would be associated with an increased risk of prostate cancer and that estradiol would be associated with a decreased risk," he said. Since SHBG "binds more to testosterone than to estradiol, we thought that the net effect of SHBG would be to reduce prostate cancer."