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An Association Between Concomitant Tamoxifen and Antidepressant Use and Breast Cancer Recurrence?

An abstract presented at the annual meeting of the American Society of Clinical Oncology suggests that women taking tamoxifen plus certain antidepressants — namely, cytochrome P450 2D6 (CYP2D6) inhibitors — might face increased risk for breast cancer recurrence. A second abstract, however, refutes this finding.

In the first study, researchers retrospectively examined a U.S. health plan's database to compare the risk for breast cancer recurrence in breast cancer survivors taking tamoxifen alone and those taking tamoxifen plus a CYP2D6 inhibitor, such as an SSRI. (Tamoxifen is metabolized by CYP2D6.) They found that use of the drug combination was associated with almost twice the risk for recurrence compared with use of tamoxifen alone.

A second, smaller study (involving some 200 women using tamoxifen and CYP2D6 inhibitors) found no such association.

Asked to comment on these preliminary findings, Journal Watch Psychiatry Editor-in-Chief Peter Roy-Byrne offers that while psychiatrists know which antidepressants inhibit CYP2D6, they may not realize that this enzyme is required to convert tamoxifen to its active form. "Practically speaking," he says, "this is only a problem with fluoxetine and paroxetine, minimally with sertraline, and not at all with citalopram or escitalopram or venlafaxine and probably not bupropion. Thus, there are a lot of choices for women receiving tamoxifen."

LINK(S):

ASCO abstract of first study (Free)

ASCO abstract of second study (Free)

Associated Press story (Free)

Published in Physician's First Watch June 1, 2009