DIVERGENT DIFFERENTIATIVE HISTOGENETIC LINES IN LUNG-TUMORS - IDENTIFICATION OF HISTOTYPES WITH PURE OR MIXED ULTRASTRUCTURAL PHENOTYPE AND THEIR PROGNOSTIC-SIGNIFICANCE

We performed an electron microscopic study of 50 lung tumors, previously diagnosed by light microscopy, and compared the results of the two techniques. Data analysis identified two ultrastructural phenotypes: pure and mixed. The former was characterized by a constant differentiative pattern and the latter by diverging differentiative histogenetic lines. We observed six differentiative lines as follows: squamous, glandular, neuroendocrine, villopodial, intestinal, and apocrine sudoriparous. Features of divergent differentiative lines were observed in 36 cases (64%), throughout the histotypes, sometimes with coexpression of more than one differentiation in a single case and/or cell. Adenocarcinoma was the histotype most frequently observed in pure form whereas most squamous cell carcinomas showed a mixed phenotype. This suggests that the histotype of the different lung tumors arises from a single glandular pluripotent cell, able to differentiate toward divergent differentiative lines. The clinical stage at onset and at the end of the follow-up indicates that the biologic behavior of lung tumors varies according to whether the ultrastructural phenotype is pure or mixed.