Tamoxifen Linked to Difficult-To-Treat Tumor

EW YORK (Reuters Health) - Breast cancer patients who take tamoxifen, a drug that can shrink tumors in half of the women who take it, have a lower risk of a cancer recurrence than those who do not take the drug. However, if a tamoxifen user develops a tumor in the other breast, it may be of a more difficult-to-treat type, according to a study released on Tuesday.

However, researchers caution that the results are preliminary and the evidence is insufficient to change current treatment practices.

Tamoxifen, an estrogen-like drug, has been found to be very effective at treating women with breast tumors that contain estrogen receptors. Such receptors trigger tumor growth in response to the estrogen in a woman's body, and blocking this effect with tamoxifen causes tumors to shrink.

In the new study, researchers found that women treated with tamoxifen were less likely to develop a new tumor in their healthy breast that was estrogen receptor-positive compared with women not given the drug. In general, women with breast cancer are two to six times as likely as women in the general population to develop a tumor in their other breast.

However, the tamoxifen-treated women seemed to be at greater risk of developing a second tumor that lacked estrogen receptors. Specifically, the tamoxifen-treated women were five times as likely to develop an estrogen receptor-negative tumor in their other breast than women who did not take tamoxifen. Tumors that lack estrogen receptors are less common and generally harder to treat than those that have the receptors.

In the study of nearly 9,000 women over 50, 89 tamoxifen users developed a second tumor, as did 100 women not given tamoxifen. Of those women, 112 had estrogen receptor-positive tumors, 20 had estrogen receptor-negative tumors and the remaining tumors could not be classified.

The findings are published in the July 4th Journal of the National Cancer Institute

According to Dr. Christopher Li and associates, from Fred Hutchinson Cancer Research Center, in Seattle, Washington, the findings could be important, given that women with estrogen receptor-negative cancer have an 8% to 35% lower 5-year survival rate than women with estrogen receptor-positive tumors.

``Since this is the first study to assess this issue in detail, further studies are required to confirm our results,'' Li told Reuters Health. ``However, even if supported, we do not believe that this finding should change current clinical practices as tamoxifen has clearly been shown to reduce the risk of recurrence and the risk of developing a second cancer and to improve survival.''

In a related editorial, Dr. Sandra Swain, from National Cancer Institute, in Bethesda, Maryland, takes issue with the study's findings, citing what she deems to be significant limitations. For example, the researchers could not determine how long the patients took tamoxifen and relies on a small number of patients for its conclusions.

``Consequently,'' Dr. Swain writes, ``the study does not provide reliable evidence that is sufficient to make any conclusions regarding the estrogen receptor status of contralateral breast cancer in women treated with tamoxifen.''

SOURCE: Journal of the National Cancer Institute 2001;93:1008-1012,963-