SSRIs and Tamoxifen: Does the Combination Increase Recurrence?

As recently reported by CTV: {excerpts from the article; data presented at ASCO May 31/09}

ORLANDO, Fla. — Breast cancer survivors risk having their disease come back if
they use certain antidepressants while also taking the cancer prevention drug
tamoxifen, worrisome new research shows...The new study, reported Saturday at a
cancer conference in Florida (ASCO), is the largest to look at the issue. It found that
using these interfering drugs -- including Prozac, Paxil or Zoloft -- can
virtually wipe out the benefit tamoxifen provides...Breast cancer recurred in
about seven per cent of women on tamoxifen alone, and in 14 per cent of women
also taking other drugs that could interfere -- mainly the antidepressants Paxil
and Prozac, and, to a lesser extent, Zoloft...No greater breast cancer risk was
seen in women taking the antidepressants Celexa, Lexapro or Luvox with
tamoxifen, and there are reasons to think that other antidepressants may be safe
as well, Epstein said..."This is a very controversial area," said Dr. Claudine
Isaacs, a breast specialist at Georgetown University's Lombardi Comprehensive
Cancer Center. "Until these data are absolutely clear, I would avoid drugs that
impact on tamoxifen metabolism."

From OncocologySTAT:

"SRIs, however, can also inhibit the 2D6 enzyme that converts tamoxifen to its
main active metabolite, endoxifen, thus possibly decreasing its efficacy."

Massachusetts General Hospital Centre For Women's Health posted an article in June '08 regarding interactions between tamoxifen and antidepressants. I discovered this post when searching for solutions after detecting the interaction via Micromedex/Lexicomp.
{Click here for link to article}.

The following table from the above mentioned article provides some guidance when faced with such a dilemma:

CPY2D6 Inhibitors

Strong Inhibitors (Should be avoided if
possible):
Paroxetine
Fluoxetine
Bupropion
Duloxetine

Moderate Inhibitors:
Sertraline
Citalopram/Escitalopram
Doxepin

Weak Inhibitors (Use not restricted by treatment with
tamoxifen):
Venlafaxine
Desvenlafaxine

If antidepressants are indicated in the treatment of a woman currently
taking tamoxifen, the following treatment recommendations have been made:
*If possible, avoid antidepressants, including fluoxetine and paroxetine, that are
strong inhibitors of the CPY2D6 enzyme (see the list of inhibitors above)
*If the antidepressant is being used solely for the management of hot
flushes, other agents, such as gabapentin, may be used instead
*If it is not possible to avoid these antidepressants, another option for postmenopausal women
only would be to switch from tamoxifen to an aromatase inhibitor, if medically
appropriate

Please post your comments below or email me at: chrisral@cancerboard.ab.ca

* Thanks to Scott Edwards, PharmD for the link to the CTV News article.