[Electron microscopic study of atypical squamous metaplasia of bronchial epithelium, bronchial carcinoma in situ and microinvasive carcinoma during development of pulmonary squamous cell carcinoma].

Cytomorphological differences among severely atypical squamous metaplasia of bronchial epithelium, bronchial carcinoma in situ and microinvasive carcinoma were examined cytologically and electron microscopically. Cytomorphological features were studied by a light microscopy and an electron microscopy in bronchial brushing and histopathological preparations obtained from a patient with bronchial carcinoma in situ and two patients with microinvasive carcinoma. Cytologically, carcinoma in situ cells showed about same size and represented round to oval nuclei whose chromatin revealed finely granular and uniform pattern. Microinvasive carcinoma cells varied markedly in size. Nuclear pleomorphism was also marked in cells whose chromatin revealed sometimes coarsely granular and irregular pattern. The ultrastructural features of microinvasive carcinoma were more irregular in nuclear outline, abundant in the number of perichromatin granules and predominant in formation of fibrillar center than those of carcinoma in situ. Cytomorphological features were studied by a light microscopy and a transmission electron microscopy in bronchial brushing and biopsy preparations obtained from bronchial carcinoma in situ and atypical squamous metaplasia induced in dogs by means of bronchial submucosal injections of 20-methylcholanthrene. Both the carcinoma in situ and the severely atypical squamous metaplasia cells showed the same cytologic findings in that cells were about same size, nuclei were round to oval in shape and chromatin was finely granular, while the nucleoli of carcinoma in situ cells were relatively prominent. However, ultrastructural features indicated that there were differences, although some similarities exist, between in situ and severely atypical squamous metaplasia in nuclear form, number of perichromatin granules and enlargement of the nucleoli. From these findings, it was suggested that there were cytomorphological differences between carcinoma in situ and microinvasive carcinoma from cytological and ultrastructural aspects. We conclude that differentiation between carcinoma in situ cells and those of severely atypical squamous metaplasia is sometimes difficult when based only on cytologic features but there were cytomorphological differences at the ultrastructural level.