Identifying the Predictive Factors of Response to PD-1 or PD-L1 Antagonists

Inclusion Criteria: 1. Age ≥18 years old. 2. Histological confirmed diagnosis of one of the following: * Non-resectable (stage III) or metastatic (stage IV) melanoma, * Metastatic, EGFR- and ALK-negative, non-small cell lung cancer with a high level of PD-L1 expression (defined as a "tumour proportion score" of greater than or equal to 50%) which has not been previously treated with chemotherapy in the metastatic setting, * Head and Neck squamous cell carcinoma that is that is recurrent or progressing following reference chemotherapy and that is not amenable to surgery or radiation therapy. 3. Indicated for treatment with a PD-1 or PD-L1 antagonist according to the European Marketing Authorisation or the conditions of a Temporary Authorisation of Use. 4. Estimated life expectancy ≥16 weeks. 5. Eastern Cooperative Oncology Group (ECOG) performance status score ≤2. 6. Presence of at least one tumour lesion (except bone lesions) accessible to biopsy, if a biopsy is required (see below). 7. Willing and able to provide a pre-treatment biopsy sample, if a biopsy is required. Note: where an archived tumour sample is available, this archived sample can be used in place of a fresh biopsy sample, if the patient has not received any antineoplastic therapy since the collection date. 8. Measurable disease according to RECIST v1.1 (Eisenhauer, 2009). 9. Beneficiary of social insurance coverage. 10. Comprehension of French. 11. Provision of written informed consent (signed and dated) prior to the initiation of any protocol specific procedure. Exclusion Criteria: 1. Any contraindication to treatment with a PD-1 or PD-L1 antagonist. 2. Any contraindication to a biopsy including: platelets \<80 x 10⁹/L, International Normalised Ratio (INR) \>1.5 or prothrombin time (PT) \>1.5 x upper limit of normal range (ULN), prolonged partial thromboplastin time (PTT) in the absence of factor XII deficiency or antiphospholipid antibodies, ongoing treatment with anticoagulants. 3. Bone metastasis as the only disease site available for biopsy. 4. Previous treatment with a PD-1 or PD-L1 antagonist. 5. Individuals deprived of liberty or placed under the authority of a tutor. 6. Any condition which in the Investigator's opinion makes it undesirable for the subject to participate in the trial or which would jeopardize compliance with the protocol.