Stereotactic ablative body radiotherapy (SAbR) for oligometastatic cancer

The metastatic state of most solid cancers traditionally has been regarded as an incurable dissemination of disease, with treatment focused on delaying progression rather than eliminating all tumour burden. In this setting, local therapies including surgery and radiotherapy are directed at quality of life end points and not at improvement in survival. However, improvements in imaging and systemic therapy have highlighted populations of patients with lower burden of metastatic disease, termed oligometastatic, who may present an exception. This condition is hypothesized to bridge the gap between incurable metastatic disease and locoregional disease, where miliary spread either has not occurred or remains eradicable. Consequently, elimination of such low-burden residual disease may cure some patients or delay further progression. Accordingly, use of local therapies with the intent of improving survival in oligometastatic disease has increased. Technological advances in radiation delivery with stereotactic ablative body radiotherapy (SAbR) in particular have provided a non-invasive and low-morbidity option. While observational studies have provided interesting preliminary data, significant work remains necessary to prove the merits of this treatment paradigm. This review discusses the data for the oligometastatic state and its treatment with SAbR, as well as challenges to its investigation.