細胞内メラニン沈着を呈した直腸神経内分泌腫瘍“pigmented carcinoid”の1例

Pigmented Carcinoid Tumor of the Rectum with Intracellular Melanin Deposition：A Case Report

要旨●患者は70歳代，男性．大腸内視鏡検査で下部直腸に黒色の平坦隆起性病変を認めた．内視鏡像は緊満感のある粘膜下腫瘍様隆起を呈しており，粘膜固有層を主座に置く腫瘍性病変を疑い，total biopsy目的でキャップ法を用いた内視鏡的粘膜切除術（EMR-C）で一括切除した．病理組織学的所見では直腸神経内分泌腫瘍（NET）G1の所見であったが，腫瘍細胞の細胞質に茶褐色の微細顆粒を認め，特殊染色でメラニン顆粒と判明した．pigmented carcinoidはNETの特殊型であり，その機序は不明であるが，NET細胞内にメラニン沈着を伴うことが特徴である．これまで気管支・肺や胸腺での報告をいくつか認めるが，本症例は消化管に発生したpigmented carcinoidの初めての報告となる．

　A 70-year-old male patient underwent colonoscopy, revealing a black-colored, submucosal tumor-like lesion, which was resected using cap-assisted endoscopic mucosal resection and histologically diagnosed as grade 1 rectal neuroendocrine tumor（NET）. Special staining identified brown-colored granules in the tumor cell cytoplasm as melanin deposits, and the lesion was classified as pigmented carcinoid, a rare NET subtype. Although the mechanism of melanin deposition in NET cells remains unclear, similar cases of pigmented carcinoid were reported in bronchi, lungs, and thymus. To our knowledge, this is the first reported case of a pigmented carcinoid originating in the gastrointestinal tract.