潰瘍型を呈した無色素性直腸肛門部悪性黒色腫の1例

A Case Report of Ulcerated Primary Amelanotic Anorectal Melanoma

要旨　患者は46歳，女性．検診で便潜血陽性を指摘され，大腸内視鏡検査で直腸肛門部に発赤調の潰瘍形成性腫瘤を指摘された．内視鏡像から低～未分化癌を疑ったが，生検診断で類円形～多角形の腫瘍細胞が充実性に増殖する像を認め，免疫染色でHMB-45（＋），Melan-A（＋）であった．メラニン色素産生は認めず，無色素性悪性黒色腫と診断した．注腸X線造影検査，超音波内視鏡検査，拡大内視鏡観察を行い，深達度MPと診断した．CT，MRI検査上はリンパ節転移や遠隔転移は認めなかった．D2郭清を伴う腹会陰式直腸切断術を施行した．「大腸癌取扱い規約」に準じ，2型，深達度MP，N0，H0，M0，Stage Iであった．潰瘍型を呈する無色素性悪性黒色腫は比較的まれであり，過去13年（1996～2008年）の本邦報告96例の検討を含め報告する．

　A 46-year-old woman had a positive fecal occult blood test at a regular check-up. Colonoscopy revealed a reddish ulcerated lesion in the anorectum. Endoscopic diagnosis was poorly differentiated carcinoma. The biopsy specimen revealed medullary proliferation of round or polygonal tumor cells, HMB45 and Melan-A positive. Pathological diagnosis was amelanotic malignant melanoma. We used barium enema, magnifying endoscopy and endoscopic ultrasonography, and diagnosed the fact that the tumor had invaded the proper muscle. Computed tomography and Magnetic resonance imaging showed neither evident lymph node metastasis nor distant metastasis.

　We perfomed Mile's operation with D2 lymph nodes dissection. According to the Japanease“General Rules for Clinical and Pathological Studies on cancer of the Colon, Rectum and Anus”, the final pathological diagnosis was Type 2, depth MP, N0, H0, M0, stage I.

　We report a comparatively rare case of ulcerated type amelanotic melanoma, and discuss 97 Japanese case reports of anorectal malignant melanoma from 1996 to 2008.