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

Purpose: 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.

Methods: 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.

Results: 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.

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