(CSPOT39) Trajectories of Antidepressant Use After Tamoxifen Initiation Among Young and Middle Age Women with Breast Cancer

Background: One in three women diagnosed with breast cancer take antidepressants during active cancer treatment but it is unclear whether patterns of utilization change following tamoxifen initiation. Variations in the utilization of tamoxifen and antidepressants in clinical practice may stem from factors such as CYP2D6-inhibition and disease severity.

Objectives: We aimed to characterize trajectories of antidepressant use after tamoxifen initiation among young and middle age women with breast cancer.

Methods: A retrospective cohort study included women, 18-64 years-old, with ductal, invasive, or metastatic breast cancer who received a new tamoxifen prescription (index date) after a 12-month baseline in which they had filled ≥2 antidepressant prescriptions. We used a 25% random sample of IQVIA PharMetrics® Plus for Academics US claims from 2007 to 2021. Antidepressant use was defined as the proportion of days covered (PDC) in each of the twelve, follow-up months after tamoxifen initiation. Group-based trajectory modeling was performed using polynomial functions of the longitudinal PDC measures. We compared 2-6-group finite mixture models to determine which model best fits the longitudinal antidepressant utilization data. Model fit was evaluated based on lowest Bayesian Information Criterion, clinical interpretability, and having ≥10% of the sample in each identified trajectory group.

Results: Our final model showed 851 women following four distinct trajectories of antidepressant use after initiating tamoxifen. Eleven percent exhibited immediately decreasing use [PDC 6% (+6)], 6% exhibited delayed decreasing use [PDC 34% (+12)], 19% initially decreased but subsequently increased use i.e., decreasing-increasing use [PDC 51% (+15)], and 63% exhibited consistently high use [PDC 90% (+8)]. Women with baseline depression were observed more frequently within the consistently high trajectory group (62%), relative to the decreasing-increasing (59%), delayed decreasing (50%) and immediately decreasing (38%) groups, p < .01.

Conclusions: Nearly 40% of women with breast cancer do not persist with prior antidepressant use after tamoxifen initiation. Future research should aim to understand predictors of trajectory group membership - to identify subpopulations that could benefit from targeted interventions to improve antidepressant adherence.