[Ultrastructural study of small cell carcinoma (author's transl)]

Fifty bronchopulmonary tumors were studied by light and electron microscopy: 39 carcinomas (25 small cell carcinomas, 8 undifferentiated carcinomas, 6 poorly differentiated squamous cell carcinomas) and 11 carcinoid tumors (5 central, 4 peripheral, 1 atypical, 1 of the tumorlet type). The results indicate that small cell carcinoma is a precise entity characterized by the presence of neurosecretory granules in the cytoplasm. Ultrastructurally carcinoid tumor resemble small cell carcinomas and there is a continuous spectrum of differentiation between the less undifferentiated neuro-endocrine tumors, i.e. the small cell anaplastic carcinomas, and the higher differentiated types, i.e. the carcinoids. The diagnostic and prognostic value of the ultrastructural findings are discussed.