大腸若年性ポリープ―前癌病変としての意義と臨床像の時代的変遷

Juvenile Polyps in the Colon and Rectum: Their Clinical Aspects and Neoplastic Potential

要旨　非ポリポーシス型の大腸若年性ポリープ（juvenile polyp；JP）74例（計79個）を臨床病理学的に検討した．若年性ポリープを母地として，1例に癌，3例に異型上皮が発生していた．異型上皮化した3例では，他の部位に進行癌や多数の異種性ポリープ（腺腫内癌，腺腫，過形成性ポリープなど）を合併していた．特に過形成性ポリープはしばしば異型を示し，豊富な炎症性間質が特徴で，この点でJPに類似していた．JPの腫瘍化や多発する異種性ポリープの合併などの事実は，非前癌病変として処理される傾向にあったJPにも，従来以上に慎重なサーベイランスが必要と思われた．

　Seventy four cases (79 lesions) of juvenile polyps (JP) were studied clinicopathologically. The age distribution of the patients was bimodal. The lowest incidence was in the third decade. The mean size of the polyps in the first decade patients (childhood group) was 18 mm, larger than in the older patients, in whom the average was 11 mm. Eighty four percent of colonic polyps were found on the left side of the colon. All the patients with JP in the childhood group experienced melena or prolapse of the polyps, while only 24% of the patients in the non-childhood group had these symptoms.

　Recently, there have been some reports that JP may, develop dysplastic or carcinoma. Our histological study detected one case of intramucosal carcinoma and three cases of dysplastic epithelium. These three cases of dysplastic change in JP had concominant carcinoma and/or polyps of different histological type in the different sites: 3 carcinoma in adenomas, 13 adenomas, 6 hyperplastic polyps with atypia and 5 hyperplastic polyps without atypia. Eleven hyperplastic polyps in the two cases were characterized by abundant stroma and an inflammatory cell infiltrate suggesting a pathogenetic sequence between these polyps and JP. It is clear that the epithelial cells of JP are capable of undergoing both neoplastic and kinetic changes.

　We propose that JP should not be considered as no risk for cancer, and that colonoscopic or barium enema examinations are necessary to follow up JP patients to detect malignant changes.