PDCD1 and cervical squamous intraepithelial neoplasia: As mentioned above, increased levels of PD-1 expression on the T-cells and APC cells, and also hyper-activation of the Wnt pathway during chronic HPV infection, are positively associated with tumor cell metastasis and HPV-associated cancers such as cervical cancer and cervical intraepithelial neoplasia (CIN) grade [1,9].