Proliferative verrucous leukoplakia (PVL) is a particular form of leukoplakia with a very high risk of malignant transformation. Therefore, this lesion may provide clues to understanding malignant transformation of the precancerous lesion "leukoplakia". To define the process of the malignant transformation of PVL, serial sections of a rare case of tongue PVL were examined pathologically, ultrastructurally, and immunohistochemically with the use of nuclear protein"Ki-67", a widely accepted

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... of cell proliferation. The patient was a 55-year-old man. The lesion was white and verrucous. The tissue showed various pathologic characteristics, such as those of simple hyperplasia, severe dysplasia, verrucous hyperplasia, and squamous cell carcinoma. Ki-67 positive nuclei increased parallel to the degree of malignancy. Ultrastructurally, the tumor cells extended cytoplasmic processes to stromal tissue, indicating a highly invasive nature. The data are presented in detail here. Moreover, based on this case, methods for treatment are discussed. We concluded that cases of PVL, such as the presented one, that were suspected clinically should be treated similarly to malignant tumors.