Management of adjuvant endocrine therapy (AET) side effects in patients with breast cancer: A single cancer center experience

e12503 Background: Up to 50% of breast cancer survivors are unable to complete the recommended 5-year course of adjuvant endocrine therapy (AET), usually due to side effects. Patients who develop side effects may change to a different medication (‘switch’) or may treat side effects with additional medications or non-pharmacologic strategies. While there are numerous evidence-based treatments available for side effects of AET, the benefit of switching AET is less well known. We have previously reported on the association between switching and early discontinuation of AET. Here, we provide further insight into the use of switching vs side effect management at our cancer center. Methods: We conducted a retrospective chart review of patients diagnosed between 2011-2014 with early stage, ER+/HER2- breast cancer. Clinical data extracted by chart review included side effects and treatment history. Patients were grouped based on whether they received a switch vs side effect management and compared for variables of interest using Chi-squared tests and confidence intervals. Multiple logistic regression was used to assess long-term adherence, adjusting for side effect type and severity. Results: A total of 228 patients with early-stage ER+/HER2- breast cancer were evaluated. Among them, 162 patients (71.0%) received treatment for side effects. A medication switch was offered in 98/162 (60.5%) cases, with side effect management (SEM) alone offered in the remaining (39.5%). Patients who switched were more likely to have reported severe side effects compared to patients who received SEM alone (OR 4.56, 95% CI (2.1, 9.8), p < 0.001). Hot flashes were more frequent in patients who received SEM compared with those switching (89% vs 59%, respectively, p < 0.001), while arthralgias were more frequent in the patients who were offered a switch (70% vs 47%, p = 0.002). ‘Other’ side effects were also more frequent in patients who switched (58% vs 30%, p < 0.001). Among patients who discontinued therapy early, the majority did so within the first 12 months (18/43, 42%). The long-term adherence rate was 73% overall, and it was significantly lower in the subset of patients who received a switch compared to those who received SEM – 62% vs 91% respectively, p < 0.001. Significance was maintained after adjusting for side effect type and severity with multiple logistic regression, p = 0.013. Conclusions: Despite limited evidence, rates of switching are high in clinical practice. Switching is more common in patients with severe symptoms, and those who report arthralgias and uncommon side effects. Switching was associated with poor long-term adherence. Due to the potential for selection bias, conclusions are limited as to whether switching itself is ineffective. A prospective randomized trial is under development at our cancer center to address this question.