Study Finds Danger With Cancer Drug

Women who take the drug tamoxifen after having cancer removed from one breast may run a higher risk of developing a relatively more dangerous form of cancer in the other breast, according to a new study.

The findings contradict previous research and are drawn from the analysis of a small number of patients, which increases the chance they may be a fluke.

Researchers at the Fred Hutchinson Cancer Research Center in Seattle report that they found clear evidence that tamoxifen significantly lowers the risk of new disease, but the study also demonstrates the need to find drugs that are effective against tumors resistant to tamoxifen.

“Half of the women who take tamoxifen develop resistance, but this resistance is not understood,” said Christopher Li of the Hutchinson center. He said the new study, appearing today in the Journal of the National Cancer Institute, is consistent with a theory that tamoxifen supports the growth of breast tumors that are not sensitive to estrogen, the female hormone.

“This is a preliminary study. My colleagues and I do not think these findings should change current therapy,” said Li, an epidemiologist.

More than half of the nearly 200,000 American women newly diagnosed with breast cancer each year will eventually take tamoxifen. The drug’s purpose is to suppress the growth of any cancer cells that may remain after the original tumor is surgically removed. A secondary goal is to prevent any new cancers from developing in the untreated breast.

Tamoxifen’s usefulness in performing both tasks is unquestioned. An analysis of 55 studies enrolling a total of 37,000 patients recently showed that taking the drug for five years cut by nearly half the chance that a woman’s original cancer would recur or that a new tumor would arise.

The new study examined the experience of about 9,000 women from the state of Washington who were treated for breast cancer during the 1990s.