Effect of adjuvant endocrine therapy: single-agent vs. switching on breast cancer-free and overall survival - a retrospective cohort study.

Background: Patients with hormone-dependent breast cancer (HDBC) are prescribed adjuvant endocrine therapy (AET) in the form of tamoxifen or aromatase inhibitors (AI), either as single-agent endocrine therapy (SAET) or with a switch between them. However, the decision to maintain either strategy remains controversial. We aimed to compare breast cancer-free survival (BCFS) and overall survival (OS) in Mexican patients with HDBC under AET, be it as SAET or switching mode. Materials and methods: We retrospectively analyzed a cohort of 300 patients diagnosed between 2009 and 2014. The association of BCFS and OS with clinical variables was analyzed with Cox and binary logistic regression models. Results: In the univariate Cox models, compared to AI-based SAET, only tamoxifen-based SAET [hazard ratio (HR): 1.93, 95% confidence interval (CI): 1.13-3.3] exhibited association with BCFS; this became non-significant in the multivariate model. In the multivariate logistic models, compared to AI-based SAET, both tamoxifen-based SAET [odds ratio (OR): 2.2, 95% CI: 1.2-4.2] and switching (OR: 2.8, 95% CI: 1.3--.9) schemes were associated with recurrence or death events. Additionally, patients with an AET duration longer than 36 (OR: 0.18, 95% CI: 0.06-0.54) and 60 (OR: 0.26, 95% CI: 0.09-0.75) months had 82% and 74% lower odds of experiencing recurrence/death, respectively. Conclusions: The data revealed discrepancies between the logistic and Cox regression models regarding the administered AET. These findings may reflect differences in patient selection, and treatment adherence or duration. The data also underscore the relevance of considering AET duration, as extended treatment (> 36 and > 60 months) consistently demonstrated protective effects regardless of regimen.