A drug already prescribed to shrink benign enlarged prostates has been shown to reduce the risk of a prostate cancer diagnosis by 23 percent in men with an increased risk of the disease, a large international trial has found. Results were reported in the New England Journal of Medicine.
The four-year study involved 8,231 men ages 50 to 75 who were randomly assigned to receive a placebo or a daily 0.5 mg dose of dutasteride (Avodart®), a drug approved to treat benign prostatic hyperplasia. Men in the study had elevated PSA levels (2.5 ng/ml to 10 ng/ml) but no evidence of cancer on biopsies performed within six months of enrolling in the trial.
“Many men every year are in the situation of having elevated PSA levels but a negative biopsy,” says the study’s lead author, Gerald Andriole, Jr., MD, chief of urologic surgery at Washington University School of Medicine and a researcher at the Siteman Cancer Center. “We know from experience that many of these men are likely to have microscopic prostate tumors that were missed by their original biopsy.”
The investigators performed scheduled biopsies on the men two years after they enrolled in the study and again after four years. Overall, 659 men (19.9 percent) taking dutasteride were diagnosed with prostate cancer, compared with 858 men (25.1 percent) taking a placebo. Among men with a family history of prostate cancer, the drug reduced the relative risk of a prostate cancer diagnosis by 31.4 percent.
“The most likely explanation for the study’s results is that dutasteride is keeping tumors small or even shrinking them to the point that they are unlikely to be detected by a biopsy,” Andriole says.
Dutasteride was most effective at reducing the risk of medium grade tumors, defined as 5 to 6 on the Gleason scale. These tumors account for the majority of all prostate cancers. Because midgrade tumors grow unpredictably, many men opt for aggressive treatment—surgery or radiation therapy—which can lead to incontinence and impotence.
The investigators found no significant increase in aggressive, high-grade tumors (defined as a Gleason score 7 to 10) among men who took dutasteride over four years.