PDCD1 and neoplasm: The strong attractive character observed in the amino-acid residues Y101HC, R102HC, F103HC, D104HC, M105HC and D108HC could give the base for the development of an improved drug targeting the PD-1/PD-L1 pathway by activating an immune resistance mechanism in response to endogenous anti-tumor activity, avoiding an immunosuppressive tumor microenvironment.