PDCD1 and nonpapillary renal cell carcinoma: We will particularly focus on the presentation of different immune checkpoint proteins expressed in ccRCC that are involved in the negative regulation of the immune response, including Programmed cell Death Protein 1 (PD-1), Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4), Lymphocyte-Activation Gene 3 (LAG-3), T-cell Immunoglobulin and Mucin domain 3 (TIM-3), and T cell immunoreceptor with Immunoglobulin and Immunoreceptor Tyrosine-based Inhibitory Motif (ITIM) domains (TIGIT).