Stereotactic ablative body radiotherapy: A paradigm shift – or even a potential cure – for oligometastatic cancer?

By Brit Cooper Jones

When you or a loved one is diagnosed with cancer – particularly cancer that has metastasized, or spread, to other sites – it can be a devastating diagnosis. Typically, once cancer has spread throughout the body, there are fewer treatment options available. It often means a cure is not possible. But there may be some hope on the horizon for patients with certain types of metastatic disease.

“Oligometastatic disease” is defined as a cancer that has metastasized to a limited number of sites. Sometimes surgery can be used to remove oligometastatic disease. But what about when surgery is not possible – perhaps because the location is too difficult to access, or because a patient’s age or other health conditions may make surgery too risky? In cases like these, stereotactic ablative body radiotherapy might represent a new option.

And what exactly is “stereotactic ablative body radiotherapy” (SABR) – also known as stereotactic body radiotherapy (SBRT)? It is a form of radiation therapy that precisely delivers high doses of radiation to specific body sites, and over a shorter treatment period than with conventional radiotherapy. The method of delivery – which relies on image guidance (e.g., X-ray, CT, or MRI) as well as a method of keeping the patient still (e.g., compression, a body frame, or an immobilization device) – is what allows these high doses to be delivered while sparing normal tissue.

SABR holds promise because of its potential to treat metastatic tumours that would be impossible to surgically remove. This, in turn, may offer a potential cure for certain types of oligometastatic cancer. (And, if not a cure, it might offer prolonged survival or, in more severe cases, palliation and symptom relief for metastatic tumours causing pain or other complications.)

However, despite the hope and promise of SABR, there remain key questions. What does the research show about the clinical effectiveness of SABR for different types of cancers and metastatic tumours (e.g., cancer that has spread to the lungs, liver, bones, or lymph nodes)? If SABR were to be funded in Canadian jurisdictions, which patients should be eligible to receive this treatment? If most of treatment centres were in urban areas, how would access to treatment be made equitable to all patients? What would the staff training requirements, equipment purchasing requirements, economic considerations, and implementation considerations be?

To help answer these questions, and to guide decisions about the optimal use of SABR for oligometastatic cancer in Canada, decision-makers and the health care community turned to CADTH – an independent agency that finds, assesses, and summarizes the research on drugs, medical devices, tests, and procedures – to find out what the evidence says.

CADTH started with a Rapid Response report (a rapid literature review with critical appraisal) that was published in February 2019. However, the report was inconclusive. Three low-quality retrospective studies and one economic evaluation were identified, but these likely did not represent the full breadth of research on the topic for two reasons. First of all, the search criteria were limited to studies that explicitly described the patient population as “patients with oligometastatic cancer.” This approach would have missed studies that did not use that exact terminology. Secondly, SABR for oligometastatic cancer is a highly active area of research with over 60 clinical trials currently underway; so additional, potentially high-quality studies may be published soon. In a supplementary literature search conducted by CADTH since the publication of the initial Rapid Response report, additional citations were already identified as the body of literature continues to grow.

CADTH is now proceeding with a health technology assessment (HTA) on the topic of SABR for oligometastatic cancer. Given the rapid evolution of this particular field, the clinical component of the HTA will take the form of a “living systematic review”. That is, CADTH will continually look for new clinical research to ensure the HTA findings remain current and reflect the most up-to-date evidence. The HTA will also include an Environmental Scan of current implementation status and practice uses, as well as barriers and facilitators to implementing SABR

Subscribe to New at CADTH to stay updated on CADTH’s latest reports, including the SABR Health Technology Assessment when it becomes available.

See CADTH’s Rapid Response report on the topic of SABR for oligometastatic cancer as well as CADTH’s Scoping Brief for the Health Technology Assessment. If you would like to learn more about CADTH, visit, follow us on Twitter @CADTH_ACTMS, or speak to a Liaison Officer in your region:

Brit Cooper Jones is a knowledge mobilization officer at CADTH.