Antidepressant can block activation of tamoxifen, resulting in higher breast cancer mortality

-- A. Agrawal, PhD

Tuesday, February 9, 2010 (Last Updated: 02/10/2010)

TUESDAY, Feb. 9 (HealthDay News) -- Women with breast cancer who take tamoxifen and the antidepressant paroxetine (Paxil), which has been hypothesized to reduce the effectiveness of tamoxifen, may be at higher risk of dying of breast cancer, according to research published online Feb. 8 in BMJ.

Catherine M. Kelly, M.D., from the Sunnybrook Health Sciences Centre in Toronto, and colleagues analyzed data from 2,430 elderly women (66 years or older) with breast cancer who were treated with tamoxifen and a single selective serotonin reuptake inhibitor, most commonly paroxetine, between 1993 and 2005.

The researchers found that 15.4 percent of patients died of breast cancer during a mean follow-up of 2.38 years. After adjusting for several factors, overlapping treatment with tamoxifen and paroxetine was associated with a higher risk of death from breast cancer, and a greater extent of overlap was associated with a greater risk of death. For the median overlap of 41 percent, the authors estimated that there would be one additional breast cancer death for every 19.7 patients within five years of stopping tamoxifen treatment.

"Paroxetine use during tamoxifen treatment is associated with an increased risk of death from breast cancer, supporting the hypothesis that paroxetine can reduce or abolish the benefit of tamoxifen in women with breast cancer," Kelly and colleagues conclude. "This observation is consistent with the critical role of CYP2D6 in the metabolic activation of tamoxifen, and highlights a drug interaction that is extremely common, widely underappreciated and uniformly avoidable."

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Specialties Oncology
Internal Medicine
Family Practice
OBGYN & Women's Health

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