To examine the possible association between epithelial proliferation and disease progression in the oral mucosa using the actual proliferation index. The actual proliferation index was measured by the Ki-67 labeling index and argyrophilic nucleolar organizer region count per nucleus. Immunohistochemistry was carried out for Ki-67 by using the molecular immunology borstel-1 clone in 20 leukoplakias, 20 oral squamous cell carcinomas, and 10 normal oral mucosae. The argyrophilic nucleolar organizer region count per nucleus, Ki-67 labeling index, and actual proliferation index were significantly higher in oral squamous cell carcinoma, followed by leukoplakia and normal oral mucosa. Leukoplakia with dysplasia showed a significantly higher Ki-67 labeling index and actual proliferation index, compared to leukoplakia without dysphasia. There was a significant correlation of Bryne's histological malignancy grading with the argyrophilic nucleolar organizer region count and the Ki-67 labeling index. There was a significant positive correlation between the argyrophilic nucleolar organizer region count and the Ki-67 labeling index among all groups. Leukoplakia or suspected epithelial dysplasia should be stained for argyrophilic nucleolar organizer regions and Ki-67. The actual proliferation index is not only useful as a prognostic factor, but could also be a promising treatment determining modality for patients with premalignant and malignant lesions.
