直腸肛門部の腫瘍性疾患―直腸肛門部の非上皮性腫瘍と転移性腫瘍

Non-epithelial Tumors in the Rectum and the Anus

要旨　直腸肛門部の非上皮性腫瘍はまれであるが，GIST，平滑筋性腫瘍，脂肪腫，リンパ腫などがある．臨床的には内視鏡や注腸X線で粘膜下腫瘍として診断される．GISTと平滑筋性腫瘍は免疫組織化学染色で鑑別される．GISTと平滑筋性腫瘍は悪性の経過をとる場合があるため拡大切除する．再発GISTにはimatinibが有効である．大腸の脂肪腫はGISTに次いで多いが，直腸の発症は少ない．通常は無治療でよいが，まれに脂肪肉腫があるのでフォローを要する．肛門部の悪性黒色腫は色素細胞から発生する皮膚癌の一種であるが，早期に転移しやすく極めて予後不良である．転移性腫瘍は血行性転移よりも近接臓器の原発癌からの転移が多い．

　Non-epithelial tumors in the rectum and the anus are very uncommon disorders, which include GIST, leiomyoma, leiomyosarcoma, and lipoma and so on. Clinically, these tumors are diagnosed as submucosal tumor by endoscopy or barium enema. GIST and leiomyoma are differentiated by immunohistochemical stain. GIST and leiomyoma should be treated as a malignant tumor, and imatinib is effective for recurrent GIST. Lipoma of the rectum is also rare. Usually no treatment is justified, but liposarcoma may have developped. Occasionally a malignant melanoma develops in the anorectal region, which has extremely poor prognosis. Metastatic tumor in the rectum is rare. Spread from adjacent primary neoplasms is perhaps more common than blood-borne spread.