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Some Antidepressants May Thwart Tamoxifen's Effect on Breast Cancer

SUNDAY, May 31 (HealthDay News) -- Common antidepressants that many breast cancer survivors use to dampen the hot flashes caused by taking tamoxifen may actually boost the odds of the disease's return, new research warns.

The finding was presented this weekend at the American Society of Clinical Oncology's annual meeting, in Orlando, Fla.

But to muddy the waters further, a second study found that the antidepressants did not impair tamoxifen's cancer-fighting powers.

Nevertheless, authors from both reports are recommending that women who have had breast cancer explore other ways to treat hot flashes.

Outside experts agreed.

"Women should talk to their medical oncologist about what antidepressant they're and what hormone therapy they're on, and make sure they're not one of the ones we're worried about," said Dr. Kelly Marcom, a breast oncologist with the Duke Comprehensive Cancer Center and director of the Duke Hereditary Cancer Clinic, in Durham, N.C.

Many breast cancer survivors take the drug tamoxifen to reduce their odds for recurrence. But tamoxifen often causes hot flashes, a side effect that can be controlled with selective serotonin reuptake inhibitor (SSRI) antidepressants such as paroxetine (Paxil) or fluoxetine (Prozac). Besides working on the neurotransmitter serotonin, these drugs inhibit an enzyme called 2D6, necessary to convert tamoxifen into its main active metabolite, endoxifen.

Women who have a gene mutation preventing the formation of 2D6 do not reap the same benefits from tamoxifen as women without the mutation, the researchers noted. Moreover, drugs that inhibit the formation of 2D6 may result in lower levels of endoxifen, although the clinical implications of that remain unclear.

The U.S. Food and Drug Administration is still weighing whether or not to add a caution about the gene variation to the tamoxifen label.

In one of the studies, Medco, a U.S. pharmacy benefits management company, reviewed the medical records of 10.7 million members of a health plan. That analysis turned up 945 women taking tamoxifen and 353 taking tamoxifen plus an SSRI/2D6 inhibitor, most commonly Prozac and Paxil.

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