Preventing metastatic recurrence in low-risk ER/PR + breast cancer patients—a retrospective clinical study exploring the evolving challenge of persistence with adjuvant endocrine therapy

PURPOSE: In the genomic era, more women with low-risk breast cancer will forego chemotherapy and rely on adjuvant endocrine therapy (AET) to prevent metastatic recurrence. However, some of these patients will unfortunately relapse. We sought to understand this outcome. Preliminary work suggested that early discontinuation of AET, also known as non-persistence, may play an important role. A retrospective analysis exploring factors related to our breast cancer patients’ non-persistence with AET was performed. METHODS: Women who underwent Oncotype-DX® testing between 2011 and 2014 with minimum 5 years follow-up were included. ‘Low risk’ was defined as Oncotype score < 26. Outcomes of recurrence and persistence were determined by chart review. Patient, tumor and treatment factors were collected, and persistent versus non-persistent groups compared using multivariable ANOVA and Fisher Chi square exact test. RESULTS: We identified six cases of distant recurrence among low-risk patients with a median follow-up of 7.7 years. Among them, five of six patients (83%) were non-persistent with AET. The non-persistence rate in our cohort regardless of recurrence was 57/228 (25%). Non-persistent patients reported more severe side effects compared with persistent patients (p = 0.002) and were more likely to be offered a switch in endocrine therapy, rather than symptom-relief (p = 0.006). In contrast, persistent patients were 10.3 times more likely to have been offered symptom-alleviating medications compared with non-persistent patients (p < 0.001). A subset analysis revealed that patients who persisted with therapy had a higher Oncotype-DX® score than patients who discontinued early (p = 0.028). CONCLUSION: Metastatic recurrence in low-risk breast cancer patients may be primarily due to non-persistence with endocrine therapy. Further work is needed to optimize care for patients who struggle with side effects. To our knowledge, these are the first published data suggesting that Oncotype-DX® score may influence persistence with AET.