[Pathology and molecular biology of lung cancer].

Therapy and prognosis of lung cancer depend crucially on tumor size, tumor stage, and the histomorphological tumor type at the time of primary diagnosis. A tumor weighing only 1 g and barely detectable by clinical examination consists of about 1 x 10(9) tumor cells. The primary histological diagnosis is generally based on small biopsies 1-2 mm in diameter, which allow the assessment of only a few up to some hundred tumor cells in a section of 4 microns. Until 20 years ago light microscopic and histochemical investigations were the basis for sophisticated morphological tumor diagnosis. In recent years electron microscopy, immunohistochemistry, cytometry, and molecular biology have extended our knowledge of the complex tumor biology, with the range of phenotypes and genotypes indicating enormous tumor heterogeneity. The value, expressiveness, and prognostic importance of these laborious and expensive techniques must be examined in studies, keeping in mind new aspects of tumor classification. Histological and cytological findings are still the decisive basis for the primary diagnosis of the pathologist in any given case.