胃ポリープの時代的変貌―病理からみて

Historical Changes of Benign Gastric Polyps

　ポリープとは，広義には「粘膜面からみた肉眼的な限局性粘膜隆起」で，その構成成分は問われない．しかし，狭義には「上皮性成分から成る肉眼的な限局性粘膜隆起」とされている．本稿ではポリープを狭義で使用する．

　さて，胃ポリープの時代的変遷を病理学的側面からみるのが著者に与えられた主題である．これには次のような種類の論点がある．

　Histologic classification of gastric polyps had been in confusion. However, in 1955 to 1965, they were roughly divided into two types: hyperplastic polyp and adenoma.

　Since about 1966 in Japan each type had been differentiated by endoscopic biopsy. Malignant transformation of benign gastric polyps had been generally believed to be high till about 1964 in the world. Many exact data on gastric polyps in resected stomachs were accumulated in Japan from 1968 to 1975. They disclosed low frequency of malignant transformation of benign gastric polyps, that is, 4～9% in adenoma and O～5% in hyperplastic polyp.

　In 1975 and 1979 long-term follow-up data emphatically declared that the malignant change was extremely rare and that benign gastric polyps, especially adenoma, grew very slowly.

　Recently patients with pure hyperplastic polyp or pure adenoma has been followed up. Polyps detected in resected stomachs are associated with or incidental to gastric carcinoma in high frequency, and it is especially so in cases with adenoma. It is due to such reasons that recent cases with carcinoma are older than the past and that differentiated adenocarcinoma is recently more numerous.

　On the contrary, American data in 1965 to 1972 showed a higher incidence of malignant transformation of adenoma, that is 22～53%. It is attributable to some differences of histologic criteria of adenoma and carcinoma between Japanese and American pathologists, and to predominance of large adenoma more than 2cm in largest dimension in American material.