Drug may prevent cancer in some

WASHINGTON — Scientists have discovered the first drug that promises to prevent prostate cancer, but deciding who should use it won't be easy: Sexual side effects aside, it may actually increase aggressive tumors in some men.

The drug is finasteride, already sold as a treatment for enlarged prostates under the brand name Proscar and, in a much lower dose, as Propecia for baldness.

Men who took Proscar daily for seven years cut their chances of getting prostate cancer by nearly 25 percent compared with men given a dummy pill, researchers reported Tuesday in the New England Journal of Medicine.

The results were strong enough that the study of 18,000 men age 55 and older, originally scheduled to run for another year, was stopped this month.

"This trial proves prostate cancer, at least in part, is preventable," said Dr. Peter Greenwald, cancer prevention chief at the National Cancer Institute, who participated in the study himself and so far is cancer-free. "It's a huge step forward."

Because 220,000 U.S. men are diagnosed annually with prostate cancer, Proscar has "extraordinary public health potential," said lead researcher Dr. Ian Thompson of the University of Texas Health Sciences Center in San Antonio.

Proscar works by preventing testosterone from changing into another hormone that fuels prostate enlargement and cancer growth. In the study, it worked equally well for men at low risk of cancer, and those at high risk — black men and those whose fathers and brothers had the disease.

But some troubling findings have critics questioning just how often Proscar should be used:

• Men who developed prostate cancer while taking Proscar were more likely to have tumors that appear aggressive, what doctors term "high grade." Some 6.4 percent of Proscar patients were diagnosed with those aggressive tumors, compared with 5.1 percent of men given a dummy pill. No one knows if it was a fluke — or if Proscar, a hormonal treatment, alters the prostate in a way that favors growth of more aggressive tumors.

• The medical importance of the overall cancer reduction isn't clear because of another quirk — researchers diagnosed prostate cancer in four times more placebo patients than expected.

Many were small, early stage tumors found only because every study participant received a prostate biopsy even if blood tests for cancer-signaling PSA were normal — biopsies that in the real world never would have occurred.