[Morphological classification of oral leukoplakia (author's transl)].

656 cases of oral leukoplakia were analysed according to macroscopic aspects, microscopic growth patterns and histologicalcytological differentiation, and the relationship to cancer of the oral cavity was studied. Homogeneous and speckled leukoplakia can be distinguished macroscopically, while flat (70%), papillary-endophytic (22%) and papillomatous-exophytic (8%) types can be distinguished by their growth pattern. Histological-cytological characteristics consist of epithelial hyperplasia (hyperkeratosis with ortho- or parakeratosis; akanthosis) and epithelial dysplasia (dyskeratosis, basal-cell hyperplasia, loss of polar arrangement of the basal cells, cell polymorphism, increased mitosis rate). No or little dysplasia was demonstrated in 74% of leukoplakias, moderate in 17% and marked in 6%. Carcinoma-in-situ, defined as high-grade dysplasia with additional loss of epithelial layering, was found in 3%. Precancerous leukoplakia (in almost 10% of cases, counting high-grade dysplasias and carcinoma-in-situ) must be delineated as a special group. Numerous correlations were found between dysplastic leukoplakias and oral cavity cancer as regards localisation, age and sex distribution. In the various leukoplakia forms there was an increased incidence of marked stroma reactions and of Candida colonisation with increased degrees of dysplasia.