A registry-based randomized screening phase II trial. A total of 68 patients with metastatic non small cell lung cancer on systemic therapy with oligoprogression to 1-5 extracranial lesions will be randomized using a 1:1 ratio to standard of care (begin next-line systemic therapy, best supportive care, continue current systemic line, based on treating physician decision) vs. receive stereotactic ablative radiotherapy to all oligoprogressive lesions while continuing their current systemic therapy.

Inclusion Criteria:

• Age ≥18 years
• Metastatic NSCLC enrolled in our CRCHUM Lung Cancer Registry and co-enrolled to the PERa registry
• Ability to provide written informed consent
• Eastern Cooperative Oncology Group (ECOG) performance status 0-3
• Oligoprogression to 1-5 extracranial lesions ≤ 5cm and involving ≤ 3 organs. Progression at the primary tumor site should be counted within the total of 5 lesions. For patients with lymph node metastases, each node is counted as one site of metastasis.
• Oligoprogression while on ICI or TKI (any line)
• Patients with brain metastasis are allowed; brain metastasis are not counted in the maximum number of lesions and should be treated as per standard of care
• All sites of disease can, in the opinion of the investigator, be safely treated and targetable with SABR (taking into account prior local therapy, organ function and underlying medical condition such as inflammatory bowel disease, pulmonary fibrosis, etc.)
• Patients with prior metastases that have been treated with ablative therapies (e.g. radiotherapy, surgery or radiofrequency ablation) before their current line of systemic therapy, are eligible.

Exclusion Criteria:

• Any lesion beyond 5 cm
• Pregnancy or breastfeeding
• Any medical condition that could, in the opinion of the investigator, preclude radiotherapy or prevent follow-up after radiotherapy.
• Presence of spinal cord compression Metastatic disease that invades the GI tract (including esophagus, stomach, small or large bowel)