A Study to Evaluate GEH200520/GEH200521 (18F) Safety and Tolerability When Used for PET Scans in Patients With Solid Tumour Malignancies

Inclusion Criteria:

• The subject is able and willing to comply with all study procedures as described inthe protocol, including the imaging day pre-visit requirements, and has read,signed, and dated an informed consent form prior to any study procedures beingperformed.

• The subject is male or female, ≥18 years of age.

• Subject has a life expectancy ≥12 weeks.

• Subject has Eastern Cooperative Oncology Group (ECOG) performance status 0-1.

• Subject has an unresectable or metastatic solid tumour or a local and resectablehead and neck squamous cell carcinoma, or an unresectable stage III-IV melanoma.

• Subject is eligible for ICI treatment per Investigator judgement.

• Subject has at least 1 measurable tumour lesion documented on CT/magnetic resonanceimaging (MRI) RECIST v1.1 during the last 12 months.

• Subject has a tumour lesion(s) of which a biopsy can safely be obtained according tostandard clinical care procedures.

• Subject is male or female that agrees to adhere to the protocol contraceptionmethods.

Exclusion Criteria:

• Subject is unable to undergo all procedures in the study and/or is unable to remainstill and tolerate the imaging procedure.

• Subject has 12-lead ECG significant findings during screening, per Investigator'sassessment.

• Subject is not stable due to medical condition or therapy that, in the opinion ofthe Investigator, could compromise subject safety or protocol objectives.

• Subject has active autoimmune disease or a documented history of autoimmune diseaseor syndrome that requires systemic steroids or immunosuppressive agents.

• Subject has serious non-malignant disease or conditions that, in the opinion of theInvestigator, could compromise subject safety or protocol objectives.

• Subject has B or T cell lymphoma.

• Subject has brain or bone-marrow metastasis that, in the opinion of theInvestigator, could compromise subject safety or protocol objectives.

• Subject has signs or symptoms of systemic infection within 2 weeks prior to imagingday.

• Subject has history of severe allergic, anaphylactic, or other hypersensitivityreactions to chimeric or humanised antibodies or fusion proteins or known allergy tothe study IMP ingredients and/or the proposed ICI therapy.

• Subject has any other diseases, metabolic dysfunction, physical examination finding,or clinical laboratory finding giving reasonable suspicion of a disease or conditionthat contraindicates the use of the ICI treatment, or that may affect theinterpretation of the results or render the subject at high risk from complications.

• Subject has laboratory values out of range per protocol.

• Subject has any safety laboratory test results (blood chemistry, haematology, andurinalysis) that, in the opinion of the Investigator, could compromise subjectsafety or protocol objectives.

• Subject has had any major surgery within 4 weeks prior to enrollment.

• Subject has been enrolled in another interventional clinical study within the 30days before screening for this study, except for the study site IIS.

• Subject is pregnant or planning to become pregnant or is breastfeeding.

• Subject has a history of alcohol or drug abuse within the last year.

• Subject has had treatment with systemic immunostimulatory agents within 6 weeks or 5half-lives of the drug, whichever is shorter, prior to dosing with the IMP.

• Subject has had treatment with systemic immunosuppressive medications within 2 weeksprior to dosing with the IMP.

• Subject has received acute, low-dose, systemic immunosuppressant medications that,in the opinion of the Investigator, could compromise protocol objectives.

• Subject has used systemic corticosteroids to treat inflammatory or autoimmunesymptoms.