ANTI DEPRESSANTS MAY LOWER EFFECTS

[Opus]

Bad combo? Some antidepressants may hamper breast cancer drug
Science News, Jan 8, 2005 by N. Seppa

By impeding estrogen's cancer-promoting properties, the drug tamoxifen has enabled thousands of breast cancer patients to fend off recurrences. But taking tamoxifen increases the frequency of hot flashes, and many women use antidepressants to limit this side effect.

Researchers now report that popular antidepressants called selective serotonin reuptake inhibitors (SSRIs) might diminish the effectiveness of tamoxifen by limiting its conversion into medicinally important agents.
Most Popular Articles
in Reference


David A. Flockhart of the Indiana University School of Medicine in Indianapolis and his colleagues there and elsewhere measured one of these compounds, called endoxifen, which binds to estrogen receptors on cells and slows cancerous growth. In the Jan. 5 Journal of the National Cancer Institute, they report that women taking tamoxifen and an SSRI had lower blood concentrations of endoxifen than did similar women on tamoxifen who weren't using an SSRI.

The scientists also determined that a woman's genes can hinder her conversion of tamoxifen to endoxifen. Women with certain variant forms of a gene called CYP2D6 showed diminished endoxifen concentrations. Lab studies had shown that the enzyme encoded by CYP2D6 is one of the substances that break down tamoxifen to create endoxifen.

About two-fifths of women have one of the enzyme-disabling variants of CYP2D6, says Flockhart. The findings could explain some of the variability in tamoxifen's effectiveness from patient to patient, he says.