Incidence of squamous metaplasia in large bronchi of Japanese lungs: relation to pulmonary carcinomas of various subtypes.

The incidence of bronchial squamous metaplasia in Japanese lungs was investigated in order to clarify the significance of this lesion for the development of lung cancer of various histological subtypes. The bronchi of 104 and 32 lungs resected, respectively, for primary or metastatic tumors were step-sectioned and examined histologically. The incidence of squamous metaplasia was particularly high (83% of cases, 8-11% of sections) in male lungs bearing primary squamous or small cell carcinoma whereas it was low (43% of cases, 3% of sections) in lungs of both sexes with adenocarcinoma, the latter figures being about the same as those for lungs with secondary metastatic tumors. Although the overall incidence of lung squamous metaplasia in Japanese is much lower than in the U.S., the present data demonstrate a high level in association with squamous or small cell carcinoma, directly comparable to that of Americans. However, atypical metaplasia, or dysplasia, was encountered much less frequently than in the U.S. A topographical study of 7 minute or small squamous cell carcinomas revealed 3 to have adjacent and 2 to have nearby areas of squamous metaplasia. However, 2 cases were found to be completely free of squamous metaplastic lesion. Thus, squamous metaplasia may be associated with the development of squamous cell carcinoma but would appear not to be an obligatory step in the development of this neoplasm.