Clinical and pathological observations have unequivocally indicated an increase in the incidence of malignant neoplasia during the last two decades. Despite important advances in surgery, radiotherapy and chemotherapy, mortality from tumours still tends to increase. Cancer research has therefore concentrated not only on early diagnosis and therapy but also, in line with recent trends in medical science, on the prevention of oncogenesis. One effi cient prophylactic approach is the treatment of preblastomatoses, which include the preneoplastic lesions of the mouth. The most frequent oral pre cancerosis, leukoplakia, has been studied extensively during the last 20 years with regard to its pathogenesis,clinical course,and response to therapy. In Hungary, studies of oral leukoplakia have a century-long tradition. The term leukoplakia was coined by the Hungarian dermatologist Ern/) Schwimmer who recognized the precancerous nature of the condition and its relationship to tobacco smoking exactly 100 years ago. In the middle of this century another Hungarian scientist, Karoly Balogh established that most leukoplakias have two stages, - reversible and irreversible - and that early lesions may heal spontaneously after the elimination of irritational factors. The incidence of leukoplakia in random population groups was determined for the first time in the world by the Hungarian investigator Pal Bruszt, and reported to be 3.6 %. Subsequent studies in other countries confirmed a range of 0.2-8.1 %, depending on geographical and environ mental conditions, way of life, and relevant habits.

Inhalt
The definition, nature and frequency of oral leukoplakia. Objectives.- I. Results of clinical follow-up studies in oral leukoplakia.- Malignant trasformation rate.- Age and Sex distribution.- Site of leukoplakia and carcinoma.- Correlation between the clinical type and malignant transformation of oral leukoplakia.- Latency period.- II. The role of etiological factors.- The etiological importance of smoking habits.- The etiological importance of mechanical factors.- The etiological importance of differences in electrical potential.- The role of inflammatory and atrophic changes of the oral mucous membrane in the pathogenesis of leukoplakia.- III. Transformations in the clinical type of leukoplakia during longitudinal studies.- IV. Comparative study of the clinical types and histological characteristics of oral leukoplakia.- Epithelial changes.- Connective tissue changes.- Comparative analysis of non-dysplastic cases.- Incidence of epithelial dysplasia and longitudinal study of leukoplakias with dysplasia.- V. Cytological studies in oral leukoplakia.- Studies of the keratinization pattern in oral leukoplakia.- The value of cytodiagnostics in the detection of cancer development from oral leukoplakia.- VI. Electron microscopic studies of oral leukoplakias.- Transmission electron microscopic (TEM) studies.- Morphometric (stereological) investigations.- Scanning electron microscopic (SEM) examinations.- VII. Oral white lesions other than leukoplakia.- Clinical (longitudinal) studies on patients with oral lichen planus.- Simultaneous occurrence of leukoplakia and oral lichen.- Investigations of white sponge naevus (leukoedema exfoliativum mucosae oris).- Morsicatio buccarum et labiorum: a clinicopathological examination.- VIII. The therapy of oral leukoplakia.- IX.Summary.- References.- Colour photos.