Treatment Strategies for Oligometastatic Breast Cancer

Abstract

Oligometastatic breast cancer, typically defined as the presence of 1-5 metastases, represents an intermediate state between locally advanced and widely metastatic disease. Emerging research suggests that oligometastatic cancer has a unique molecular signature distinct from widely metastatic disease, and that it carries a superior prognosis. Owing to its more limited capacity for widespread progression, oligometastatic disease may benefit from aggressive ablative therapy to known metastases. Options for ablation include surgical excision, radiofrequency ablation, and hypofractionated image-guided radiotherapy (HIGRT). The phase II SABR-COMET trial, which enrolled patients with oligometastatic disease of multiple histologies and randomized them to HIGRT vs. standard of care, found a notable survival advantage in favor of HIGRT. Other data suggest that HIGRT may synergize with immunotherapy by releasing powerful cytokines that increase anti-tumor immune surveillance and by recruiting tumor infiltrating lymphocytes, helping to overcome resistance to therapy. There are many ongoing trials exploring the role of ablative therapy, most notably HIGRT, with or without immunotherapy, for the treatment of oligometastatic breast cancer.We believe that patients with oligometastatic breast cancer should be offered enrollment on prospective clinical trials when possible. Outside the context of a clinical trial, we recommend that select patients with oligometastatic breast cancer be offered treatment with a curative approach, including ablative therapy to all sites of disease if it can be safely accomplished. Currently, selection criteria to consider for ablative therapy include longer disease-free interval from diagnosis to metastasis (>2 years), fewer metastases, and fewer involved organs. Undoubtedly, new data will refine or even upend our understanding of the definition and optimal management of oligometastatic disease.

Keywords: Ablative therapies; Breast cancer; Oligometastasis; Radiosurgery; SABR; SBRT.