CTLA4 and cancer: Tumour immune escape at this stage of the cancer immunity cycle occurs most often as a result of the inhibition of several key mechanisms and proteins, i.e., CTLA-4-mediated intracellular regulatory pathways, such as p38 MAPK/NF-ĸβ(p65), PI3K/AKT and Mdm2/p53, cyclin-dependent kinase inhibitors p27KIP1, p21CIP1/WAF1, CDK (cyclin-dependent kinase) inhibitors CDK4/6 and G1/S-specific cyclin-D3 [347,348,349,350].