Kelly, C., Juurlink, D., Gomes, T., Duong-Hua, M., Pritchard, K., Austin, P., & Paszat, L. (2010). Selective serotonin reuptake inhibitors and breast cancer mortality in women. BMJ, 340, c693.

Researchers sought to show that  some SSRI antidepressants reduce tamoxifen’s effectiveness by inhibiting its bioactivation by cytochrome P450 2D6 (CYP2D6).

The study enrolled postmenopausal women with breast cancer using tamoxifen therapy and a single SSRI antidepressant (paroxetine fluoxetine, sertraline, citalopram, fluvoxamine, or venlafaxine.)

The study included women living in Ontariowho were 66 years or olderand treated with tamoxifen for breast cancer between 1993 and 2005 and with a single SSRI. (24,430 women were identified; 2,430 entered into study; mean age was 74 years).

Inclusion criteria: Postmenopausal women with breast cancer newly treated with tamoxifen (defined as no tamoxifen prescription in the preceding year) and a single SSRI antidepressant (paroxetine fluoxetine, sertraline, citalopram, fluvoxamine, or venlafaxine)

Exclusion criteria: Antidepressant use of duloxetine or escitalopram

Ontario Cancer Registry provided the data.

This was a retrospective cohort study.

The study examines the total duration of tamoxifen therapy (index date: date tamoxifen was last dispensed plus an additional 60 days) and the extent to which co-prescription of potentially interacting medications occurred during the course of treatment. The primary outcome was death from breast cancer

Of 2,430 women treated with tamoxifen and single SSRI, 374 (15%) died of breast cancer during follow up. Absolute increases of 25%, 50%, and 75% in the proportion of time on tamoxifen overlappingthe  use of paroxetine were associated with 24%, 54%, & 91% increases in the risk of death from breast cancer. (p < 0.05) No such risk was seen with other antidepressants

Reported study limitations included lack of information on breast cancer stage and lack of information on indication for antidepressant use.