PTEN and neoplasm: The PD-1/PD-L1(B7-H1) interaction leads to the inhibition of local anti-tumour immunity through the attachment of a phosphate residue to PD-1 and the recruitment of protein tyrosine kinases, e.g., protein tyrosine phosphatases (PTPs), including SHP2, these being the enzymes that remove groups from phosphorylated tyrosine residues on proteins of key cell pathways, such as PI3K/AKT/mTOR and Ras-Raf/MEK/ERK.