Hyperplasia of distal airway epithelium due to aging among residents in the area where the incidence of lung cancer is high.

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(1) We scrutinized the histological changes of lungs obtained from surgical materials or autopsy cases of the people in Okinawa and Nagasaki where lung cancer is prevailing and compared them with that in Chiba where the incidence of lung cancer is relatively low. (2) The lungs from Okinawa had multiple hyperplastic foci of distal airway epithelium and its severity was great. (3) The incidence of hyperplastic foci was low among Chiba residents. Although the incidence of lung cancer among Nagasaki residents was high, the incidence of hyperplastic foci was as low as that among Chiba residents. Therefore, the high incidence of hyperplastic foci is specific not to the area where lung cancer is prevailing but to the lungs from Okinawa residents. (4) Although the origin of both hyperplastic foci and lung cancer is speculated to be proliferative epithelial cells, there was no histological evidence that the former was antecedent of the latter. Hyperplastic foci was observed more frequently in the lung of adenocarcinoma than in that of epidermoid carcinoma and atypical hyperplastic foci had close histological resemblance to adenocarcinoma. (5) Theseverity of hyperplasia was greater as the age of the people increased. This tendency was similar to the fact that the incidence of lung cancer becomes higher as the age of the patients increases. (6) We studied the changes of lungs of stray dogs in Okinawa, but lung cancer was rarely observed. However, hyperplastic foci were observed showing the possibility that there are external causes which are responsible for this change. We must examine the lungs of dogs in otherareas to prove this possibility. (7) There was no relationship between smoking and the occurrence of hyperplastic foci. Not only the importance of external causes but that of internal causes must be evaluated to clarify the reason of high incidence of lung cancer in Okinawa. We are now continuing the research focusing on the possible internal causes.