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CHICAGO – Many men with prostate cancer put off using chemotherapy as long as possible, fearing its side effects.

But a new study has found that men given chemotherapy early in their treatment for advanced disease lived a median of nearly 14 months longer than those who did not get early chemotherapy. The result could upend the established treatment practice, researchers said here Sunday.

“We haven’t seen survival benefits like that for any therapy in prostate cancer,” said Dr. Michael J. Morris, an associate professor at the Memorial Sloan-Kettering Cancer Center, who was not involved in the study but was selected to publicly comment on it at the annual meeting of the American Society of Clinical Oncology.

Another study presented Sunday found that drugs called aromatase inhibitors might be better than the standard drug tamoxifen in preventing a recurrence of disease in premenopausal women with early breast cancer.

Both studies were featured in the plenary session Sunday, meaning they were deemed among the most noteworthy of the more than 5,000 studies presented at the meeting. In a conference that typically celebrates the latest and greatest drug, all four studies chosen for the plenary session this year are about better ways of using older drugs, showing that there can be a lot to learn even after drugs get to market.

Dr. Nicholas J. Vogelzang, an author of the study on prostate cancer, said that the findings would change practice and that he had already started discussing this option with patients. The challenge, he said, is getting men to agree.

The study’s findings apply to a fairly narrow group of patients – men whose cancer has already spread beyond the prostate gland at the time of diagnosis, or whose cancer has come back after surgery or radiation treatment and still remains susceptible to hormone therapy.

The study, sponsored by the National Cancer Institute, involved 790 men who received either hormone therapy only or hormone therapy in addition to at most six infusions of docetaxel spaced three weeks apart.

Those who received the chemotherapy lived a median of 57.6 months, compared with 44.0 months in the control group, a difference of 13.6 months. The difference in survival was even greater – 17 months – for the patients whose cancer had spread more extensively. Morris of Sloan-Kettering said those men were the best candidates for early chemotherapy.

Aromatase inhibitors are generally considered a better choice than tamoxifen for postmenopausal women. But aromatase inhibitors work only when women have low estrogen levels, which usually rules them out for premenopausal women.

The new study – actually two studies being analyzed together to accumulate nearly 4,700 patients – involved suppressing the functioning of the ovaries so that the younger women could take an aromatase inhibitor.

Five years of an aromatase inhibitor in addition to ovarian suppression proved superior to five years of tamoxifen in addition to ovarian suppression. After five years, 91.1 percent of those who received the aromatase inhibitor, exemestane, were free of cancer, compared with 87.3 percent of those who received tamoxifen with ovarian suppression. (In the United States, tamoxifen is typically used without ovarian suppression.)

Some experts said they were a bit skeptical that the results would change practice, noting that so far there was no difference between the groups in how long the women lived. And side effects must be evaluated, they said. Those include both the joint pain caused by aromatase inhibitors as well as the hot flashes and bone loss that could come from putting women into early menopause so they could use the aromatase inhibitor.