Finasteride reduces the risk for prostate cancer and it may improve the probability of early diagnosis of aggressive tumors that do develop by improving the efficacy of digital rectal examination, according to an article in the September 18 issue of the Journal of the National Cancer Institute.

Previous work had shown that finasteride is effective for benign prostatic hypertrophy and reduces the risk of developing prostate cancer by 25 percent. The current study, from the Southwest Oncology Group, strongly suggests that finasteride also raises the probability that physicians will find fast-growing prostate cancers at an early stage.

“It appears that a man concerned about prostate-cancer risk, who is having a prostate-specific antigen test on a regular basis, will not only reduce his risk of prostate cancer if he takes finasteride, but will help find the cancers that pose the highest risk,” said Ian M. Thompson, MD, the study’s senior author and a urologist at the University of Texas Health Science Center in San Antonio.

"This report provides an important interpretation of results that confounded an overall favorable interpretation of the Prostate Cancer Prevention Trial initially, and should help lessen fears that finasteride somehow causes more aggressive prostate cancer,” added Frank L. Meyskens, Jr., MD, Southwest Oncology Group associate chair for cancer control and prevention.

The Southwest Oncology Group, headquartered at the University of Michigan and one of the nation’s largest National Cancer Institute-sponsored clinical trial networks, conducted the study to further analyze data from its National Cancer Institute-sponsored 18,882-man seven-year Prostate Cancer Prevention Trial, which in 2003 found that finasteride was an effective prevention agent. The Food and Drug Administration has not approved finasteride for use in cancer prevention; the drug is approved for treating enlarged prostates.

Four years ago, Southwest Oncology Group researchers closed the Prostate Cancer Prevention Trial (PCPT) early to report that finasteride could decrease risk for prostate cancer by roughly 25 percent.

But that positive overall result - which potentially could keep around 50,000 men from developing prostate cancer each year ? was clouded by a troubling finding: Men who took the drug but still developed prostate cancer by the end of the study had higher rates of high-grade tumors than did men in the placebo group.

The follow-up study, along with two others published recently, strongly suggests that finasteride makes it easier for physicians to detect high-grade cancers early by improving screening tests and prostate biopsy itself. The two previous studies show that finasteride improves the effectiveness of the two main measures of possible problems: digital rectal examination and the prostate specific antigen blood test, which measured hormone changes associated with the disease. In some men who have low prostate specific antigen test results, cancer is present but not found in time.

“Finasteride makes the prostate specific antigen test perform better, so we can find the cancer earlier,” Thompson said. “Our current study also shows that by shrinking the prostate gland, finasteride makes a biopsy more sensitive for any cancers that are present.” That increased accuracy is very important, he adds, because if a biopsy reveals a slow-growing cancer but fails to spot a fast-growing one, a doctor and patient may take a “wait and see” approach when prompt treatment is actually needed.

In part because of concerns about possible drawbacks, most urologists, when asked about finasteride, say they seldom prescribe it as a prevention drug, despite the positive 2003 findings, Thompson said. Now, with several studies allaying concerns about the drug’s possible drawbacks, including concerns about sexual dysfunction, Thompson believes men should be told routinely about the potential benefits of finasteride when they come to the doctor’s office for screening in much the same way patients at risk of heart disease are told about the benefits of statin drugs.

Researchers in the follow-up study analyzed tissue from biopsies and in men in the finasteride and placebo groups to compare hormonal levels and disease extent. They compared prostate size at the time of biopsy in the two groups. They also examined tumor grade and extent in men in the study who went on to have their prostates removed.

They found no significant differences in degenerative hormone changes when they examined high-grade tumor biopsies in men in both groups. However, the men taking finasteride had smaller prostates. Their biopsies correctly identified a higher proportion of high-grade tumors found later when their prostates were removed compared with men in the placebo group.

In the study, the researchers concluded that finasteride may have contributed to the increased rate of high-grade cancers detected in the earlier trial by making the prostate smaller, helping the biopsy find the cancer. They did not find evidence that the drug caused changes in tumor composition that might contribute to aggressive cancer, although they don’t entirely rule out the possibility that finasteride may have led to high-grade prostate cancer in some men in the study.

“The results suggest that high-grade cancer was detected earlier and was less extensive in the finasteride group than in the placebo group,” the researchers concluded.