Paroxetine Does Not Reduce Tamoxifen’s Effectiveness in Breast Cancer Survivors

Breast cancer survivors who suffer from depression can safely take both tamoxifen and a concomitant selective serotonin reuptake inhibitor (SSRI) antidepressant, according to a large population-based observational study presented at the 2013 annual meeting of the Multinational Association of Supportive Care in Cancer.

Depression affects about half of all women with breast cancer, and many of them take antidepressants to alleviate their mood symptoms. Depressed mood is a potential side effect in women with estrogen receptor–positive (ER+) breast cancer who are typically treated with hormonal therapy to prevent recurrence.

So, while tamoxifen reduces the risk of breast cancer, it can also have effects on mood that lead women to use antidepressants. SSRIs, however, are known to inhibit CYP2D6, an enzyme needed to metabolize tamoxifen, raising concerns about whether concomitant SSRIs interfere with the protective effects of tamoxifen. However, no large studies had previously addressed breast cancer recurrence in women who take both tamoxifen and antidepressants.

“Depression is commonly treated with antidepressants, especially SSRIs. Women and their providers can gain reassurance from this study that using an SSRI and tamoxifen at the same time does not pose a greater risk of breast cancer recurrence,” stated lead author Reina Haque, PhD, of Kaiser Permanente Southern California.

About 7000 women in the Kaiser Permanente managed care system are diagnosed with breast cancer each year, she explained. “Nearly 50% of women with a recent breast cancer diagnosis experience depression, and the incidence of depression increased 4-fold in breast cancer survivors compared to women with no history of breast cancer,” she said.

The present study, Antidepressants and Breast Cancer Pharmacoepidemiology (ABC2), examined this association in a cohort of 16,887 breast cancer survivors diagnosed between 1996 and 2007, and followed through 2009. The study was based on electronic health records of these survivors. Median age at diagnosis was 63 years; about 6% had ductal carcinoma in situ; 50% had stage I disease; and 44% had stage II.
Subsequent breast cancer was reported in 2946 women; 2504 developed recurrent or metastatic disease, and 457 developed contralateral breast cancer.

A multivariate analysis found no in- creased risk of subsequent breast cancer among 16,887 women who took both paroxetine and tamoxifen for at least 25% of the days for each of the 5 years on tamoxifen. The same results were found among 12,076 women with good adherence to tamoxifen who also took paroxetine for at least 25% of the 5 years of tamoxifen treatment.

“Using one of the most complete pharmacologic databases of insured patients, we observed no significantly increased risk of subsequent breast cancer in women who used paroxetine and tamoxifen concurrently. This study demonstrates the safety of using SSRIs and tamoxifen together,” Haque stated. “This study has implications for clinical decision-making and improving quality of life among breast cancer survivors,” she said.

Reference
Haque R, Shi J, Fletcher SW, et al. Tamoxifen & antidepressant drug interactions in a cohort of breast cancer survivors cared for in large healthcare delivery systems in California. Support Care Cancer. 2013;21(suppl 1):S205. Abstract 0586. Presented at: 2013 Multinational Association of Supportive Care in Cancer Annual Meeting; June 27-29, 2013; Berlin, Germany.