All patients will undergo two 89Zr-atezolizumab PET scans, one at baseline and one after two doses carboplatin induction treatment. The 89Zr-atezolizumab PET scan will be performed 4 days after tracer injection. Procedures within the ImaGelato study will be completed after the two 89Zr-atezolizumab PET scans, but patients will continue treatment with carboplatin combined with atezolizumab in the GELATO trial.

Patients receive a total amount of 10 mg unlabeled atezolizumab, this will be added to the tracer to prevent rapid clearance during imaging. A labeled dose of 37 Megabequerell (MBq) 89Zr-atezolizumab (±10%; 1 Millicurie) will then be administered. The tracer will be administered intravenously (i.v.). All patients will undergo two 89Zr-atezolizumab PET scans, one at baseline and one after two doses carboplatin induction treatment. After each tracer injection, 89Zr-atezolizumab PET scans will be performed on day 4 (96 ± 6h after tracer administration).

Change in tumor uptake between 89Zr-atezolizumab PET scan at baseline and after two carboplatin induction treatments, defined as decline or increase of standardized uptake value (SUV) of 30% or more, described as per lesion and per patient. For the two different time points we will calculate the SUV for all lesions and patients. Relative decrease or increase in SUV units between different time points will be calculated for all lesions and patients, and recorded as percentage of SUV decrease or increase.

Relation of 89Zr-atezolizumab tumor uptake (at baseline, after carboplatin induction, and change between the two scans) per lesion and per patient with response to carboplatin-atezolizumab per lesion and per patient. For the 89Zr-atezolizumab PET scans, uptake will be quantified with SUV units for both time points.