Cancer Experts Say Tamoxifen Still Safe Despite New Potential Risk

Washington, DCThe complicated world of pharmaceutical drugs was further complicated yesterday after a drug commonly used for the treatment of breast cancer—and still regarded as safe—was found to potentially carry a new risk.

A new study published yesterday in 'Cancer Research' revealed that tamoxifen, which blocks the effects of estrogen, also increases the odds that long-term users could develop an uncommon, but aggressive new tumor.

According to a summary of the findings published this morning in the New York Times, women who were long-term users of tamoxifen were potentially four times as likely as nonusers to develop a new tumor that was not estrogen-sensitive. Such tumors are rare, with one in seven women studied developing a cancer in the second breast actually having the kind of tumor that fell into that category.

However, for the women affected the tumor, albeit rare, is harder to treat.

There are several caveats. The same study, which assesses the likelihood of developing a new cancer in the second breast, found that women who took tamoxifen for five years or longer were 60 percent less likely than nonusers to develop a new estrogen-sensitive tumor in the second breast and 40 percent less likely to develop a new tumor of any kind in the second breast.

And medical experts were quick to point out that the study disagrees with gold-standard clinical trials that have repeatedly found that tamoxifen reduced the recurrence and spread of common breast cancers. Given that the study was an observational study only, the findings should not affect current clinical practise due to the fact benefits of tamoxifen, manufactured by Astra Zeneca and marketed under various trademarks, are well established.

"All treatments have risks associated with them," said Dr. Christopher I. Li, an associate member of the Fred Hutchinson Cancer Research Center in Seattle and the first author of the study. "Here we're adding another potential risk to the risk side of the equation for tamoxifen. But the broader context is that tamoxifen lowers a patient's risk of dying of the disease."

Cancer experts are reported to have expressed concern that the findings, which one doctor described as a potential 'statistical fluke,' would prompt current tamoxifen patients to stop taking the drug.

They should do no such thing. Dr. Eric Winer, director of the breast oncology center at the Dana-Farber Cancer Institute in Boston said,"We know from other studies that in this setting, tamoxifen is able to lower the chance the cancer will spread to other parts of the body and improve overall survival."