PDCD1 and colorectal carcinoma: The receptors/surface enzymes that play such a dominant role in CRC include PD-1, T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT), TGFβ receptor II, glycoprotein A repetitions predominant (GARP), CD39, CD73, A2A adenosine receptors, and C-C motif chemokine receptor 8 (CCR8).