Trajectories of antidepressant use after tamoxifen initiation among young and middle-aged women with breast cancer

Antidepressant treatment patterns may change after women with breast cancer (BC) initiate tamoxifen, potentially impacting health outcomes. We characterized trajectories of antidepressant use after initiating tamoxifen among young and middle-aged women with BC, identifying risk factors for trajectory group membership.

A retrospective cohort included women 18–64 years-old with BC and antidepressant treatment history who received a new tamoxifen dispensing (index date). We measured longitudinal antidepressant use post-index date as 12, monthly, proportion of days covered (PDC) measurements in a 25% random sample of IQVIA PharMetrics® Plus for Academics US claims, 2006–2022. Group-based trajectory models identified latent subgroups of antidepressant use by testing 2–6-group representations; the best model fit determined by the lowest Bayesian Information Criterion, clinical interpretability, and each subgroup comprising ≥ 5% of the cohort. Using multinomial logistic regression, baseline covariates including demographics, depression status and the CYP2D6-inhibitory strength of antidepressants were evaluated as risk factors for the trajectory of antidepressant use after tamoxifen initiation.

Our sample of 851 women followed four distinct antidepressant adherence trajectories after tamoxifen initiation: 12% exhibited immediately decreasing use [mean PDC (sd) 8% (± 7)]; 7% exhibited delayed decreasing use [41% (± 14)]; 20% exhibited dynamic-moderate use [54% (± 15)]; and 60% exhibited consistently high use [91% (+ 7)]. Age, depression, and treatment with non CYP2D6-inhibiting antidepressants were associated with women’s trajectory of antidepressant use after initiating tamoxifen.

Nearly 40% of women were nonadherent to antidepressants after tamoxifen initiation. Future research should explore cancer-related and mental health implications of this nonadherence.