上行結腸に認めた鋸歯状病変由来と考えられる早期内分泌細胞癌の1例

Colorectal Neuroendocrine Carcinoma Arising from a Serrated Polyp, Report of a Case

要旨●患者は70歳代，女性．横行結腸癌の術前評価目的に行った下部消化管内視鏡検査で，上行結腸に10mm大の中心部に陥凹を伴う隆起性病変を認めた．隆起の立ち上がりは急峻で，中心部の陥凹の左側と比較して右側に一段高い隆起を認めた．色素拡大観察では陥凹内部は無構造でVN型pit，陥凹右側の隆起部で鋸歯状変化を伴うIV型pit，開II型pitを認めた．鋸歯状病変由来のSM深部浸潤癌を疑ったが小病変であり，EMRでの一括切除を施行した．病理組織学的には内分泌細胞癌（神経内分泌癌）の成分が主体であり，右側の隆起部に一致して鋸歯状腺腫と高〜中分化管状腺癌の併存を認め，鋸歯状病変由来の内分泌細胞癌と診断した．本邦からの鋸歯状病変由来の早期大腸内分泌細胞癌の既報はなく，非常にまれな症例と考え報告する．

　A 73-year-old woman with advanced transverse colon cancer was referred to our hospital for surgical management. Colonoscopy revealed another lesion in the ascending colon ; a 10-mm diameter sessile polyp with central depression was observed. Magnifying endoscopy with narrow-band imaging demonstrated an amorphous pattern with loose vessels in the area of the central depression. Chromoendoscopy showed that the area of the central depression and peripheral edge showed type V_N（nonstructure）and dilated type II pit patterns, respectively. Although the endoscopic diagnosis indicated submucosal invasive cancer, an EMR（endoscopic mucosal resection）was performed because of the small size of the lesion.

　Histopathological evaluation revealed a neuroendocrine carcinoma invading the deep submucosal layer（pT1）, with lymphatic and venous infiltration at the center of the lesion. The periphery of the lesion was a serrated polyp characterized by the presence of serrated adenomatous crypts with mucin-rich cytoplasm. An immunohistochemical evaluation showed that the neuroendocrine carcinoma region was strongly and diffusely positive for synaptophysin and CD56. The Ki-67 index was 80%. Subsequently, right hemicolectomy was performed, and the advanced transverse colon cancer was diagnosed as neuroendocrine carcinoma based on the histopathological evaluation.