Exploratory Interventional Study of Prognostic Serum Biomarkers of Cancer Progression

Primary objective To study the relationship between the blood levels of soluble PDL1 and β2-microglobulin measured at the diagnostic stage, and the clinical course of a metastatic solid tumor (non-small cell lung cancer, kidney cancer, or melanoma) treated with a 1st line therapeutic immune checkpoint inhibitor. The secondary objectives are: * To study the relationship between the blood levels of soluble PDL1 and β2-microglobulin measured during treatment, and the clinical course of a metastatic solid tumor treated with a first-line therapeutic immune checkpoint inhibitor. * To study the correlation between the soluble PDL1 level and the tumor PDL1 level. * To study the correlation between the blood levels of soluble PDL1 and β2-microglobulin. * To study the relationship between the blood levels of soluble PDL1 and β2-microglobulin measured during the treatment, and the tolerance of treatment with immune checkpoint inhibitor in 1st line therapy.