Arguments for a histogenetic classification of lung carcinomas

Taking into consideration the common origin of lung carcinomas from the basal-intermediate cells of covering epithelia of bronchi and bronchioles (which have preserved their ability to divide and differentiate under different stimuli), and the development of tumors in at least two phases, the main histogenetic characteristics of lung carcinomas are discussed. There are pointed out the various and multiple promoting factors acting at the level of proliferating cell foci resulted from the initiating action of chemical carcinogens and the varied deepness of the cellular changes induced. Under these conditions, the malignantly transformed cells may remain poorly differentiated, like during the histogenesis of macrocellular carcinomas (which might be influenced in the course of proliferation, within some limits, by active factors), they may preserve the stereotype of cylindrocubic development, like during the formation of cylindrocubic carcinomas (bronchiolo-alveolar cell carcinomas included), or may suffer metaplastic changes and form subsequently epidermoid carcinomas; the inclusion of Kultschitzky-APUD cells within proliferating foci may lead to bronchial carcinoids or to microcellular carcinomas. The particular forms of lung carcinomas (giant celled, adenocystic, mucoepidermoid) histogenetically reflect the mixed or concomitant stereotypical evolutions of basal cells while preserving some secretory possibilities.