Men who took finasteride, already prescribed under the brand name Proscar to treat enlarged prostates, daily for seven years cut their chances of getting prostate cancer by nearly 25 percent, the study found.
“These are very important results. This is the first intervention that has proved to reduce a man’s risk of prostate cancer,” lead researcher Dr. Ian Thompson of the University of Texas Health Sciences Center at San Antonio told a news conference Tuesday.
The results were pronounced enough that the National Cancer Institute, who sponsored the study of 18,000 men age 55 and older, stopped the trial this spring, a year ahead of schedule.
The New England Journal of Medicine will publish the results of the study in its July 17, 2003 issue, but researchers announced the findings Tuesday to coincide with the early termination of the trial.
During the study, scientists found that 18 percent of those who took finasteride developed prostate cancer — compared with 24 percent of men who took the placebo.
Finasteride, which is also sold in a lower-dose form as the baldness drug Propecia, works by preventing testosterone from changing into another hormone that fuels prostate enlargement and cancer growth.
Although the research appeared to show finasteride did prevent some prostate cancers, many doctors emphasized that it is still unclear whether men should take the drug to avoid the disease.
Men who developed prostate cancer while taking finasteride were more likely to have more aggressive — or “high grade” — tumors. Some 6.4 percent of finasteride patients were diagnosed with those aggressive tumors, compared with 5.1 percent of men in the control group. Researchers were unable to determine if finasteride, a hormonal treatment, alters the prostate in a way that favors growth of more aggressive tumors.
“The reason men on finasteride had more high-grade tumors is currently unknown, but the researchers are studying several possibilities… The drug affects the appearance of prostate cancer cells, and this may lead to a false estimate of tumor grade, which is determined visually by a pathologist.” the National Cancer Institute said in a statement.
Study leader Thompson assessed finasteride’s effectiveness with an estimate: track 1,000 men starting at age 63, and 60 of them will get prostate cancer by age 70, and 18 of those cancers will be high-grade. Give those same 1,000 men finasteride every day, and only 45 would get prostate cancer by age 70 — but 22 of them would be high-grade, he said.
The study also found many more men had developed small, early-stage tumors than expected. Researchers diagnosed prostate cancer in 24 percent of men in the study who were taking placebos, a rate four-times higher than usual.
Doctors found many of these cancers because every study participant received a prostate biopsy even if the blood tests doctors often used to screen for prostate cancer came back normal. In a traditional setting, researchers said doctors would not have ordered the further tests.
“It looks like Proscar prevented little tiny, insignificant cancers, but did nothing for high-grade cancers or maybe even allowed them to become more common,” cautioned Dr. Peter Scardino of New York’s Memorial Sloan-Kettering Cancer Center, in an editorial accompanying the research. “That doesn’t sound like a very good trade-off to me.”
The study did not gauge whether taking finasteride helped men live longer, added Dr. Herman Kattlove of the American Cancer Society, who predicted a “huge debate” over the use of the drug.
“If it were free of side effects, it would be another story,” he told the Associated Press, citing the impotence and loss of libido reported among finasteride users.
Researchers agreed the treatment needed to be discussed by doctors and patients.
“There are very few prevention strategies that are not trade-offs,” said Thompson, stressing that the use of finasteride is an individual decision based on their own risk of prostate cancer and tolerance of the drug’s side effects.
Prostate cancer kills almost 29,000 men in the U.S. each year. The risk of cancer increases with age, but there is currently no accurate way to predict who needs aggressive therapy and who has a slow-growing, unthreatening tumor. Treatments cause major side effects such as incontinence and impotence.