Histological classification and histogenesis of lung cancer

This article includes a summary on the present state of histological classifications and histogenetic aspects of malignant lung tumours. The development of histological classifications during the past 50 years is presented in brief retrospect. Based on the 1981 WHO classification, such frequent histological tumour types as squamous cell carcinomas, small cell carcinomas, different types of adenocarcinomas, and large cell carcinomas, are discussed with the aid of selected microphotographs. Histochemical and electronoptical findings are considered. Discussed in particular are the difficulties of a uniform histological grading, as well as the frequency and categorization of combined tumour types. The consideration of histogenetic aspects is supported by morphological and epidemiological findings, and the results of animal experiment on preneoplastic mucosal lesions. DNA measurements on the heterogeneity and polyclonality of tumours are discussed in light of recent developments.