IMMUNOSABR is geared towards opening up a new paradigm in treating metastatic cancer by obtaining clinical proof of concept for a novel bi-modal curative treatment strategy. High precision stereotactic ablative radiotherapy (SABR) is combined with immunotherapy to form a powerful synergistic anti-tumour strategy. The approach relies on the direct cytotoxic effect of SABR, the abscopal effect of radiation observed at distance from the irradiated metastatic site(s), and the effect of the tumour-specific immunocytokine L19-IL2 (watch our animation explaining the concept at https://youtu.be/6wDE6RkrikA). Palliative treatment is the current standard of care for patients with metastatic non small cell lung cancer (NSCLC), unless there is an actionable mutation. By using the concept of limited metastatic disease (≤10 sites, WHO 0-1: “oligo+”) we aim to develop a therapy with curative intent. IMMUNOSABR will gather evidence for the clinical efficacy of our bi-modal treatment strategy in a multicentre randomised phase II study (clinicaltrials.gov no. NCT02735850) in patients with limited metastatic NSCLC. IMMUNOSABR is complemented by two strong biomarker work packages which focus on developing an ambitious personalised biomarker strategy, to identify patients who can benefit from the novel treatment strategy. This includes promising non-invasive imaging techniques and state-of-the-art immunological monitoring approaches on tumour tissue and blood. IMMUNOSABR will spur further development of L19-IL2 as a commercial drug and translate the bi-modal treatment strategy towards clinical implementation.