Breast Cancer Drug Tamoxifen Appears To Raise Risk Of Developing New Type Of Tumor, Study Finds

Main Category: Breast Cancer
Also Included In: Endocrinology
Article Date: 27 Aug 2009 - 5:00 PDT

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Breast cancer patients taking a long-term course of the estrogen-blocker tamoxifen, which has been used widely to prevent recurrences of hormone-sensitive breast cancer, might have four times the risk of developing "an uncommon but aggressive" new tumor that is not estrogen-sensitive, according to a new study published Tuesday in the journal Cancer Research, the New York Times reports. According to the Times, the study by Christopher Li -- an associate member of the Fred Hutchinson Cancer Research Center in Seattle -- and colleagues was an observational study and not a randomized, controlled clinical trial.

For the study, the researchers analyzed medical histories of more than 1,000 women who were diagnosed with estrogen-sensitive breast cancer between ages 40 and 79. Most of the women who took hormonal therapy used tamoxifen. The researchers compared data on 358 women who developed a new tumor in the second breast with 674 women who did not. After comparing data, the researchers found that the women who took tamoxifen for five years or more were 60% less likely than those who had not to develop a new estrogen-sensitive tumor in the second breast and 40% less likely to develop a new tumor of any kind in the second breast, according to the Times. In addition, women in this group "were possibly four times as likely as nonusers to develop a new tumor that was not estrogen-sensitive," the Times reports. Such tumors often are uncommon and more difficult to treat. One in seven of the women who developed tumors in the second breast had this particular type of tumor, the study found.

The Times reports that some experts have questioned the study's findings because only a small number of women developed the new, unusual tumor and those who took tamoxifen for up to four years did not experience the problem. "You have to keep in mind, this drug isn't being given to women to prevent cancer in the other breast -- it's to prevent cancer from spreading to the bones and the liver and the lungs," Eric Winer, director of the breast oncology center at the Dana-Farber Cancer Institute, said. He added, "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."

In addition, the new study's authors also suggested that their findings should not change how the drug has been used because its benefits have been widely noted, the Times reports. Li said, "All treatments have risks associated with them," adding, "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" (Caryn Rabin, New York Times, 8/26).

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