The respiratory epithelium. V. Histogenesis of lung carcinomas in the human.

One hundred human primary lung carcinomas were studied by light and electron microscopy and by light microscopic histochemistry to demonstrate mucosubstances. The tumors were classified histogenetically and were grouped into three major categories depending on their cell of origin: 1) tumors from basal and/or mucous cells; 2) tumors from neurosecretory cells; and 3) tumors from Clara cells. Most carcinomas (88%) arose from basal and/or mucous cells. These were subdivided into epidermoid carcinomas (21%), combined epidermoid and adenocarcinomas (46%), and adenocarcinomas (21%). The criteria for epidermoid differentiation included the presence of tonofilament bundles, poorly developed endoplasmic reticulum and Golgi apparatus, and well-developed desmosomes. The criteria for adeno differentiation included well-developed endoplasmic reticulum and Golgi apparatus, poorly developed desmosomes, the presence of extracellular and/or intracellular alveoli, and/or other evidence of cellular secretion such as secretory granules. In adenocarcinomas with extracellular alveoli, typical junctional complexes were also present at the luminal aspect where the cell apexes bordered the alveolus. With these criteria, combined epidermoid and adenocarcinomas were the most common type of lung carcinoma. We anticipate that the new data will clarify categories such as small cell anaplastic carcinoma and large cell carcinoma of the World Health Organization classification. In addition, the histogenetic classification of lung tumors may be of value in the future in studies of risk factors, prognosis, prevention, and treatment of lung cancer.