Study: Drug Fights Late Recurrence Of Breast Cancer

TORONTO -- A study found that an additional drug prevented breast cancer from coming back after survivors thought they had the disease beaten.

The drug letrozole is for women whose cancers grow in the presence of the female hormone estrogen. It inhibits the formation of estrogen.

In a clinical trial including more than 5,000 women worldwide, a daily letrozole pill was prescribed to women whose cancer had been spotted early, and who had completed five years on another estrogen inhibitor, tamoxifen.

Participants in the clinical trial were enrolled through hospitals, cancer centers and institutes throughout Canada, the United States, England, Belgium, Ireland, Italy, Poland, Portugal and Switzerland.

Living five years without a recurrence is a standard milepost for successful treatment for most cancer types, but breast cancer can recur even after that. While tamoxifen is widely used to prevent breast cancer recurrence in postmenopausal women, it stops being effective after five years because, researchers believe, tumors become resistant to it.

However, the Canadian-led international clinical trial found that women who got letrozole had about half as many recurrences compared with women who did not get letrozole.

The clinical trial was halted early because of the positive results, and researchers are notifying the 5,187 women worldwide who have participated in the study. Women on letrozole will continue taking the drug and those on the placebo can begin taking the drug if they wish.

The study was released online Thursday by the New England Journal of Medicine.

"More than half of women who develop recurrent breast cancer do so more than five years after their original diagnosis," said Dr. Paul Goss, the study's lead researcher from Princess Margaret Hospital in Toronto. "For years, we have thought that we had reached the limit of what we could do to reduce the risk of recurrence with five years of tamoxifen. Our study ushers in a new era of hope by cutting these ongoing recurrences and deaths from breast cancer after tamoxifen by almost one half."

The side effects of letrozole are very similar to those experienced by women undergoing menopause. They were generally mild in study participants. Women in the study will continue to be followed to more thoroughly assess any effects of long-term use of letrozole on bone strength or other organs.

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