Background

Antidepressants are co-prescribed with tamoxifen at rates around 30%, to manage depression, anxiety and menopausal symptoms that are commonly encountered in breast cancer.  CYP2D6 converts tamoxifen to its most active metabolite, endoxifen.  Some antidepressants inhibit CYP2D6, raising concerns that they may reduce tamoxifen’s efficacy, increasing breast cancer recurrence and mortality.  However, research to date on clinical outcomes has yielded conflicting results and remains inconclusive.  Our study explores how Australian oncologists interpret and apply this conflicting evidence in their clinical practice.

Methods

A cross-sectional survey with quantitative and qualitative components was designed and pilot-tested.  It was distributed electronically by COSA to it's breast cancer interest group (140 doctors, various disciplines), then MOGA (to 425 medical oncologists).  Survey Monkey collected responses between September 2011 and January 2012.  Data was analyzed by descriptive statistics, with two researchers independently coding qualitative information.

Results

80 clinicians participated: 77.5% (62) were medical oncologists, 10% (8) surgical, and 6.3% (5) radiation oncologists.  Depression was the leading indication for co-prescribing antidepressants and tamoxifen, followed by menopausal symptoms, then anxiety.  87.3% (69) of subjects reported being aware of potential interactions between tamoxifen and certain antidepressants, while 12.7% (10) were not aware.  87.3% (62) cited venlafaxine as their preferred antidepressant with tamoxifen; while citalopram, mirtazapine, desvenlafaxine, and escitalopram were mentioned less frequently.  Regarding antidepressants to avoid with tamoxifen: 42.5% (31) listed paroxetine, 38.4% (28) fluoxetine, 13.7% (10) ‘SSRIs’, 11% (8) sertraline, and 4.1% (3) ‘CYP2D6 inhibitors’.  23.3% (17) of respondents reported they would not avoid any antidepressants due to concerns about interactions with tamoxifen.

Discussion

Most participants were concerned about potential interactions and observed cautions to avoid using strong CYP2D6 inhibitors, particularly paroxetine and fluoxetine, with tamoxifen.  However, awareness was suboptimal and further research is required, particularly regarding newer antidepressants like duloxetine and bupropion, which were rarely mentioned by clinicians despite being moderate and strong CYP2D6 inhibitors, respectively.  For postmenopausal women, aromatase inhibitors may be preferable to tamoxifen if CYP2D6-inhibiting antidepressants are considered essential.

No disclosures.