Wednesday July 30 6:49 PM EDT

-- A combination of radiation therapy and a drug that reduces testosterone secretion improves the survival chances of men with locally advanced prostate cancer, a new study shows.

Use of the drug goserelin along with pelvic irradiation resulted in 17% greater five-year survival (79% versus 62%) than radiation alone.

Moreover, the study reported in this week's issue of The New England Journal of Medicine, found the proportion of surviving patients who were free of cancer at five years was also greater in the combination treatment group -- 85% versus 48% in the radiation only group.

Because the hormone testosterone is associated with the development of prostate cancer, some men whose disease threatens to extend beyond the gland itself undergo orchiectomy -- surgical removal of the testes. Because the testes are the main site of testosterone production, the surgery results in drastically reduced blood levels of the hormone. But treatment with goserelin also effectively reduces testosterone production, thus offering an alternative to surgery.

An international team of researchers led by Dr. Michel Bolla of University Hospital in Grenoble, France, say studies have shown that blocking testosterone often helps keep advanced localized prostate tumors in check when patients are also treated with radiation.

But the researchers say "the question remains whether hormonal therapy should be reserved for relapse or used early in asymptomatic (without symptoms) patients with locally advanced disease who are receiving external radiation treatment."

The new study sought to determine if the drug would significantly improve disease-free and long-term survival if started early in treatment -- during the first week of radiation -- compared with radiation alone.

The researchers randomly assigned 415 men, most of whom had advanced localized prostate cancer, to receive either external pelvic radiation therapy (over seven weeks) or radiation combined with goserelin. Patients ranged in age from 51 to 80, and were followed for about 45 months.

Bolla and his collaborators found that the men given the combined treatment had better "local control" (97% versus 77%) of their cancer -- that is, it remained within the prostate capsule. More of them also had freedom from disease at five years (85% versus 48%), and better overall (five-year) survival -- 79% versus 62%.

Commenting on the report, Drs. John Blasko and Paul Lange of the University of Washington in Seattle note that the difference in five-year survival "is a finding unique to this study."

However, they caution that there may be an unwanted long-term effect after drug treatment is stopped; specifically, "suppression of testosterone may last a long time and can sometimes be permanent," especially in men who have had some radiation to their testes during prostate treatment.

"Here, quality of life issues are key, because the long-term side effects of (stopping testosterone production) are important," Blasko and Lange explain. Without testosterone, men lose body hair and beard growth, skin becomes smooth, and sexual drive and performance reduced.

In addition, they point out that more studies are needed to determine if the combination treatment helps prevent the spread of cancer cells throughout the body.

SOURCE: The New England Journal of Medicine (1997;337:295-300, 340-341)