For example, Ries et al compared PD-1 and PD-L1 expression in OLK that had undergone malignant transformation within 5 years and in OLK without malignant transformation, finding that increased levels of PD-1 and PD-L1 are related to malignant transformation in OLP and may represent a promising prognostic indicator to determine the risk of malignant progression of OLK within 5 years 69. The gene discussed is PDCD1; the disease is oral lichen planus.