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.

Transient commensal clonal interactions can drive tumor metastasis.

The extent and importance of functional heterogeneity and crosstalk between tumor cells is poorly understood. Here, we describe the generation of clonal populations from a patient-derived ovarian clear cell carcinoma model which forms malignant ascites and solid peritoneal tumors upon intraperitoneal transplantation in mice. The clonal populations are engineered with secreted Gaussia luciferase to monitor tumor growth dynamics and tagged with a unique DNA barcode to track their fate in multiclonal mixtures during tumor progression. Only one clone, CL31, grows robustly, generating exclusively malignant ascites. However, multiclonal mixtures form large solid peritoneal metastases, populated almost entirely by CL31, suggesting that transient cooperative interclonal interactions are sufficient to promote metastasis of CL31. CL31 uniquely harbors ERBB2 amplification, and its acquired metastatic activity in clonal mixtures is dependent on transient exposure to amphiregulin, which is exclusively secreted by non-tumorigenic clones. Amphiregulin enhances CL31 mesothelial clearance, a prerequisite for metastasis. These findings demonstrate that transient, ostensibly innocuous tumor subpopulations can promote metastases via "hit-and-run" commensal interactions.