Antidepressant May Interfere With Breast Cancer
The selective serotonin reuptake inhibitor (SSRI) paroxetine (Paxil®) may decrease the effectiveness of tamoxifen, a drug used to prevent and treat breast cancer, a new study suggests. The longer paroxetine use overlapped with tamoxifen treatment, the higher the chances of untimely death related to breast cancer. To put it in perspective, the researchers estimate that one extra breast cancer death would occur within 5 years of stopping tamoxifen treatment for every 20 women using both drugs 41% of the time during treatment.
What’s the danger? Paroxetine may diminish tamoxifen’s cancer-fighting effects. It inhibits a key enzyme, CYP2D6, involved in converting tamoxifen to its active form.
These findings, published in BMJ, have major implications, assert the study authors. The prevalence of depression among women with early breast cancer is roughly twice that of the general female population. In addition, SSRIs are prescribed to women taking tamoxifen to reduce hot flashes.
In this particular study, no risks were seen with other antidepressants. But the researchers note that SSRIs inhibit CYP2D6 to varying degrees and may reduce tamoxifen’s effectiveness. Fluoxetine (Prozac®), for example, is also a strong inhibitor of CYP2D6.
The bottom line: Tamoxifen is beneficial for breast cancer treatment. In women with early stage estrogen-receptor positive breast cancer, tamoxifen reduces the risk of recurrence by about half and the risk of breast cancer death by about a third. If you’re taking tamoxifen and paroxetine or fluoxetine, talk to your doctor about switching to an antidepressant that shows little or no inhibition of CYP2D6.