KRT13 and squamous cell carcinoma: However, in mucosal epithelium without any morphologically recognizable dysplasia, either classic or differentiated, retained CK13 expression defines patients with a very low risk for malignant transformation, since none of the 22 patients without morphological recognizable dysplasia with retained CK13 staining developed squamous cell carcinoma, within a follow-up after initial oral leukoplakia diagnosis of at least 9 years.