MEDICINE / PROSTATE CANCER : High Rate of Disease Linked to Enzyme
An enzyme that acts on the male hormone testosterone may play a role in the development of prostate cancer and lead to new approaches in the prevention and treatment of the disease, according to a new USC study.
The researchers found that native Japanese men, who have some of the lowest rates of prostate cancer in the world, have far less activity of the enzyme than black Americans, who have one of the highest rates of the cancer. White Americans, who have intermediate rates of prostate cancer, had similar activity of the enzyme to black Americans.
“Understanding these international variations goes a long way toward understanding the underlying cause of prostate cancer,” said the leader of the research team, Dr. Ronald K. Ross of USC’s Kenneth Norris Jr. Comprehensive Cancer Center.
The findings will be published Saturday in The Lancet, a British medical journal.
The enzyme, known as 5 alpha reductase, converts the male sex hormone testosterone to another hormone, dihydrotestosterone, which controls the division of cells in the prostate. Dihydrotestosterone is believed to play a key role in the development of prostate cancer as well as non-cancerous enlargement of the prostate gland, which is common in men over 50.
The USC study involved laboratory analysis of blood samples obtained from 50 white and 50 black university students from the United States as well as 54 Japanese medical students. According to Ross, young adults were chosen for the study because the researchers wanted to see if the enzyme levels could predict the ethnic groups at greatest risk of developing the disease.
By two measures, the activity of the enzyme was found to be “substantially and significantly higher” in blacks and whites than in Japanese.
The researchers could not explain why the activity of 5 alpha reductase enzyme appeared to be similar in blacks and whites. However, they found that blacks had testosterone levels about 15% higher than those of whites and Japanese. The higher testosterone levels of black men, which have been reported previously, may be related to the higher rates of prostate cancer among blacks than whites, Ross said.
The study did not examine the prevention or treatment of prostate cancer. But Ross said he hoped that the results would spur investigation of drugs that block the enzyme’s action. These drugs are known as 5-alpha reductase inhibitors.
One such drug, known as finasteride, is under development by Merck & Co. of Rahway, N.J., as a treatment for non-cancerous prostate enlargement. A spokeswoman for Merck said that although there are “theoretical reasons” why this type of drug may be helpful for prostate cancer as well, the necessary studies had yet to be conducted.
The American Cancer Society estimates that 132,000 cases of prostate cancer will develop in American men in 1992 and 34,000 men will die from the disease.
