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Article Title

Tamoxifen and Antidepressant Drug Interactions in a Large Cohort of Breast Cancer Survivors

Publication Date

4-30-2015

Keywords

breast cancer, medical treatment

Abstract

Background/Aims: Considerable controversy exists on whether certain antidepressants reduce tamoxifen’s effectiveness in lowering recurrence or subsequent breast cancer. Previous studies have been limited by small sample sizes, poor measurement of medication use, or inadequate statistical analysis. Our goal was to determine whether taking tamoxifen and antidepressants concomitantly is associated with an increased risk of subsequent breast cancer in survivors.

Methods: We assembled a cohort of 16,887 women who were diagnosed with their first primary breast cancer (Stage 0–II) from 1996 to 2007 and treated with tamoxifen and followed through 12/31/2009 at Kaiser Permanente Southern and Northern California. We collected demographic, tumor, pharmacy and cancer treatment information. The outcome measure was risk of subsequent breast cancer. The main independent variables were fractions of overlap when both tamoxifen and antidepressant treatments were prescribed. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated using Cox regression models.

Results: Overall, 2,946 women (17%) developed subsequent breast cancer during the 14-year study period. We observed a small nonsignificant increased risk of subsequent breast cancer in women who concurrently used paroxetine in the first full year of tamoxifen use. For every 25% increase in percent days overlap of tamoxifen and paroxetine use, the risk increased insignificantly by 6% (HR: 1.06, 95% CI: 0.98–1.14). However, the risk attenuated with longer tamoxifen duration.

Discussion: We observed a slight increased risk of subsequent breast cancer in women who concurrently used paroxetine in the first year of endocrine therapy. Nevertheless, taking tamoxifen for a longer duration mitigated such risks.

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