Histological features of differentiated dysplasia in the oral mucosa: a review of oral invasive squamous cell carcinoma cases diagnosed with benign or low-grade dysplasia on previous biopsies.

The diagnosis of oral squamous cell carcinoma is sometimes delayed. Recently, the concept of differentiated dysplasia in the oral mucosa was proposed, and we attempted to elucidate the histologic features of differentiated dysplasia in the oral mucosa. Two pathologists reviewed 38 small biopsy cases of patients diagnosed with benign to low-grade dysplasia in the first biopsy, but were diagnosed with invasive carcinoma after excisional biopsy within 2 years. Of these, 29 cases were suspected of having differentiated dysplasia, which histologically showed "abnormal variation in nuclear size and shape," "increased number and size of nucleoli," and "loss of polarity of basal cells." In addition to the features observed in classic dysplasia, "premature keratinization in single cells" and "loss of epithelial cell cohesion" were characteristically observed. These 2 findings were often observed only in the lower half of the epithelium, but not in the full layer of the epithelium. Histological findings of oral differentiated dysplasia were very similar to those of differentiated vulvar intraepithelial neoplasia. "Premature keratinization in single cells" and "loss of epithelial cell cohesion" are specific pathological findings of oral differentiated dysplasia. Oral differentiated dysplasia is considered as a part of the broad spectrum of oral dysplasia that exhibits morphological characteristics different from classic dysplasia rather than being a separate entity. The diagnosis of oral differentiated dysplasia is expected to reduce the delayed diagnosis and improve the prognosis and post-treatment quality of life of patients with oral cavity cancer.