New concepts and insights into the role of radiation therapy in extracranial metastatic disease

Abstract

Stereotactic ablative radiotherapy (SABR) is a form of very precise radiotherapy that delivers high doses to tumors while sparing adjacent organs at risk. Recent data show that SABR is a low-toxic and highly effective local treatment for metastatic localizations in various organs, obtaining local control rates of approximately 80%. Experimental evidence also suggests that SABR may play an important therapeutic role in oligometastatic/oligorecurrent/oligoprogressive patients, a subset of cancer patients who are probably in an intermediate disease state between localized disease and widespread dissemination. There is a strong biological and clinical rationale in combining the high local control rates achievable with SABR with effective systemic therapies, and recent results of pilot studies indicate that SABR may have a potential impact on prognosis in this subgroup of patients, being ‘curative’ in around 20–25% of cases. This paper reviews and discusses basic concepts and clinical applications of SABR in oligometastatic patients.

Keywords::

• biology of metastases
• extracranial metastases
• oligometastases
• radiosurgery
• stereotactic ablative radiotherapy

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • An increasing number of patients present with oligometastatic disease at diagnosis, or oligoprogressive/oligorecurrent disease after systemic and/or locoregional first-line therapies.

• • Fractionated or single-fraction stereotactic ablative radiotherapy (SABR) is safe and effective in controlling metastatic nodules arising in different organs, and represents a valid alternative to surgery. Local control is approximately 80%. Multiple sites can be treated simultaneously over a few days.

• • A longer disease-free interval, breast cancer histology, less than three metastases are factors associated with a better outcome after SABR.

• • The combination of SABR and systemic therapies may potentially offer an advantage in progression-free survival and overall survival, as demonstrated by preliminary experiences. The safety is not proven for all agents and the combination is not established as superior to systemic therapy alone or SABR alone.

• • Current and future prospective trials will clarify the impact of ablative therapies in combination with systemic therapies on clinical outcomes in oligometastatic patients.