Analysis of the histological findings on an objective basis, using a cluster analysis programme, provided an encouraging degree of separation into the diagnostic groups. When a number of known carcinoma cases were included in the cluster analysis as " markers ", a small number of leukoplakia and keratosis cases were placed by the computer into the same cluster as these " markers ". Of the original 187 cases originally diagnosed as leukoplakia or keratosis, 4.8% are known to have developed a carcinoma, but of the 11 cases the computer placed in the same cluster as the " marker " cases of carcinoma, 36% have subsequently developed carcinoma. Thus, in the cluster analyses, the computer is tending to " recognize " those cases that later developed carcinoma, and to separate them from the bulk of the cases in which malignant change has not occurred.
An immunocytochemical study was carried out on normal salivary gland tissue and ten salivary gland pleomorphic adenomas. Antibodies to myosin were used to stain myoepithelial cells. Duct cells were stained using an antibody to total keratin and a subpopulation of basal duct cells with an antibody to 45/46K keratins. Basement membranes were stained with anti-type IV collagen. The results demonstrated that myoepithelial cells are relatively rare in the majority of pleomorphic adenomas and that many of the cells which have been classically described as myoepithelial in routine histological preparations do not clearly show this type of differentiation. However, the tumors presented a spectrum of differentiation patterns from those that were mainly ductal to the rare tumour which was largely myoepithelial. It is further suggested that the 45/46K keratin antibody is capable of identifying a subpopulation of cells which could possibly be important in the histogenesis of this tumour.
SUMMARY.-In a retrospective survey of 235 cases in which the diagnosis on biopsy was lichen planus, keratosis or leukoplakia, the histological features were re-assessed as objectively as possible and without reference to the original diagnosis.The tissue changes were recorded under39 headings, and many were assessed on a roughly quantitative basis. In addition, two clinical features were included; whether the biopsy was from the buccal mucosa (as opposed to some other intraoral site) and whether the lesions involved multiple intraoral sites. For each possible pair of diagnostic categories (keratosis and leukoplakia, lichen planus and keratosis, lichen planus and leukoplakia) the recorded findings were subjected to discriminant analysis in order to provide a quantitative assessment of the value of each individual feature for discriminating between the two diagnostic groups. The computer programme also provided for the application of these calculated values to yield a " score " for each case, and for an assessment of the significance of the separation of the diagnostic groups thus achieved. In general, the values calculated by the computer for the discriminatory value of each tissue change accorded with our subjective impressions, but a number of features that were given a relatively high value had not previously been recognized as important in differential diagnosis.A discriminant analysis was also performed on those cases of leukoplakia known to have later developed a carcinoma, in comparison with the leukoplakia cases that did not develop carcinoma. High values were accorded mainly to the well-known features of epithelial atypia, but a similar high value was indicated for the presence of Russell bodies. We had not previously realized that the presence of Russell bodies was of prognostic significance in this context. When the total scores for the groups of cases were analysed, it was found that the separation of each pair of diagnostic groups was significant at the 1% level. The separation of leukoplakia cases that subsequently developed carcinoma, from those that did not develop carcinoma, was significant at the 5% level. In this latter analysis, a better separation might be achieved with larger numbers of cases, but there will always be the complicating factor that an unknown number of leukoplakia cases would develop carcinoma if the patient had received no treatment.IN previous papers (Kramer et al., , 1970Kramer, 1969) we have shown that cluster analysis, applied to the process of histopathological diagnosis, enabled us to examine the validity of certain aspects of our diagnostic criteria. Dis-
An antiserum against epithelial membrane antigen has been used to stain a variety of lesions arising in the salivary glands. In normal major and minor glands staining was localised to the ductal systems. There was no evidence of myoepithelial cell staining. The mucous elements of the submandibular and sublingual glands were negative, but in the mucous elements of the minor glands there was focal cytoplasmic positivity. There was no cytoplasmic staining of serous elements in major or minor salivary glands. In pleomorphic adenomas the luminal membrane of ductal elements was strongly positive, with focal cytoplasmic positivity in some myxoid areas. In mucoepidermoid tumours both adjacent cell membranes and cytoplasm were strongly positive. The ductal structure of adenoid cystic carcinomas were clearly delineated while the pseudoducts produced by enclosed areas of stroma were negative. All mesenchymally derived tumours were negative and a tumour previously considered as a chondroma was strongly positive. The results are discussed in relation to phenotypic heterogeneity and the histogenesis of salivary gland tumours.
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