Use of Breast Cancer Drug Beyond 5 Years Discouraged : Medicine: Tamoxifen provides little benefit beyond that time and could be harmful, officials say. But it’s a ‘potent weapon’ when used early.

The National Cancer Institute on Thursday warned against prolonged use of the widely prescribed breast cancer drug tamoxifen, saying that taking it provides little benefit after five years and could be harmful.

New studies showed no difference in benefit for women with early breast cancer who stopped after five years on the drug, compared to those who continued longer, the institute said. Furthermore, research has indicated that the drug increases chances of developing uterine cancer, the institute reported.

But institute officials stressed that tamoxifen produces “a proven survival benefit” for early breast cancer patients when taken for a period shorter than five years. The drug is widely used after breast cancer surgery as additional therapy to prevent recurrence of the disease.

“Tamoxifen remains one of our most potent weapons against breast cancer and these new results should in no way diminish its use,” said Dr. Jeff Abrams of the institute’s division of cancer treatment and diagnosis.

Breast cancer is the most common cancer among women, with 182,000 new cases diagnosed this year and 46,000 deaths. It is the second most deadly cancer for women after lung cancer.

The new recommendation, sent to 22,000 oncologists nationwide in a “clinical alert,” will only affect women with early breast cancer. It will have no impact on use of the drug in a continuing major study of its preventive effects on 16,000 women who do not have breast cancer but are at high risk of developing it, the institute said.

In this trial, which began in 1992, researchers hope to determine whether using tamoxifen also can prevent heart disease and make bones less susceptible to fractures. The study was designed to limit tamoxifen use to five years.

“This new information does not affect the overall risk/benefit profile seen for five years of tamoxifen use and supports our continued evaluation of this drug as a possible preventive agent in the context of a well-designed clinical trial,” said Dr. Leslie Ford of the institute’s division of cancer prevention and control.

Moreover, its use in the prevention study is “based on the premise that the benefits of tamoxifen will outweigh the risks of the drug in women who are at increased risk of breast cancer,” she said.

The institute’s action followed a decision by the National Surgical Adjuvant Breast and Bowel Project to halt a clinical trial comparing the use of tamoxifen over a period of five years to its use over 10 years.

That study looked at use of the drug after surgery by women whose cancer had not spread to adjacent lymph nodes and whose cancer cells have sites that bind to and interact with estrogen. Researchers found no additional benefit for women taking tamoxifen for more than five years.

Those findings were supported by a second trial conducted in Scotland that showed significant survival benefit after five years, as well as cardiovascular benefits. But women who stopped taking the drug after five years had a lower rate of cancer recurrence (70%) than those who continued tamoxifen treatment longer (62%), the institute said.

“The results of the Scottish trial are less definitive . . . but the trend in results favoring five years of treatment supports our recommendation to stop adjuvant tamoxifen therapy at five years,” Abrams said.

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In women with an initial breast cancer, tamoxifen use for as long as five years also has been shown to reduce the risk of a second breast cancer in the opposite breast by about 40%, the institute said.

However, some clinical studies have shown that the drug can raise the risk of developing uterine cancer two to three times that of the general population, similar to that of post-menopausal women who take estrogen replacement therapy. Thus, because there are no demonstrable benefits to taking the drug beyond five years, women should stop after that time, the institute said.

Patients taking tamoxifen are routinely urged to report any unusual vaginal bleeding to their physicians, since this could be an early warning sign of uterine cancer, and annual examinations by a gynecologist are strongly recommended, the institute said.