Patient description: The patient is a 35-year-old woman with myasthenia gravis, class IIa. She complains of diplopia and fatigue and weakness that affects mainly her upper limbs. She had a positive anti-AChR antibody test, and her single fiber electromyography (SFEMG) was positive. She takes pyridostigmine 60 mg three times a day. But she still has some symptoms that interfere with her job. She is a research coordinator and has 3 children. Her 70-year-old father has hypertension. She does not smoke or use illicit drugs. She drinks alcohol occasionally at social events. Her physical exam and lab studies were not remarkable for any other abnormalities. BP: 110/75 Hgb: 11 g/dl WBC: 8000 /mm3 Plt: 300000 /ml Creatinine: 0.5 mg/dl BUN: 10 mg/dl Beta hcg: negative for pregnancy

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  NSCLC Stage IV Metastatic Disease Oligometastatic disease (≤5 metastases) Histological confirmed limited metastatic adult NSCLC patients, regardless of the PD-L1 status Maximum of 5 metastatic lesions, maximum two brain lesion with a total cumulative diameter of 5cm is allowed. SOC baseline imaging e.g MRI and/or PET-CT and CT-brain or MRI brain and/or CT-scan with at least covering thorax-upper abdomen-brain, within 6 weeks prior to randomisation. If a patient has unclear lesions in the liver or brain an MRI would be advised following the ESMO guidelines. o In patients with 2 lung tumours, it can be unclear if the patient has 2 concurrent primary tumours or a primary lung tumour with 1 metastasis. In this case, the local multidisciplinary tumour board will decide whether the patient has an M1 disease or not. • Previous treatment: Prior cancer treatments are allowed but must be discontinued for at least 4 weeks before randomisation. In case of maintenance chemotherapy, this therapy will only be started after the end of the L19-IL2 treatment or only in case of Anti-PD(L)1 treatment, during L19-IL2 therapy Age of 18 years or older WHO performance status 0-1 Adequate bone marrow function, evaluated in the local laboratory (Lab): Absolute Neutrophil Count (ANC) of ≥ 1.0 x 109 /L, platelet count ≥ 100 x 109/L, Haemoglobin (Hb) ≥ 6.0 mmol/L (or 9.67 g/dL) (it is allowed to give a blood transfusion if Hb is initially too low) Adequate hepatic function (evaluated in the local lab): total bilirubin ≤ 1.5 x upper limit of normal (ULN) for the institution; ALT, AST, and alkaline phosphatase ≤ 2.5 x ULN for the institution or ≤ 5 in case of liver metastasis) Adequate renal function (evaluated in the local lab): creatinine clearance of at least 40 ml/min Adequate endocrine (TSH, FT4) function, local guidelines The patient is capable of complying with study procedures  More than 10 metastatic lesions More than 2 brain metastatic lesions brain metastases with a cumulative diameter larger than 5 cm Patients with non-infectious pneumonitis, uncontrolled thyroid disease, pleuritis, pericarditis and peritonitis carcinomatosis Patients who received live vaccines 30 days or fewer prior to enrolment Patients who are already actively participating in another study Patients who need simultaneous radiation on the primary tumour and metastatic lesion(s). For these patients it might be an option to treat the primary tumour first although this is not mandatory for this study. There must be minimal four weeks between last treatment and randomisation Whole brain radiotherapy (WBRT) is not allowed, although it is accepted when given at least 4 weeks prior to randomisation or after the treatment period. Patients with stable brain metastases are not excluded Previous radiotherapy to an area that would be re-treated by (SAB)R, resulting in overlap of the high dose areas Maintenance therapy with Anti-PD(L)1 treatment combined with chemotherapy is not allowed during treatment ((SAB)R and L19-IL2 cycles)