论文信息 - A CASE OF ANORECTAL c-kit POSITIVE AMELANOTIC MELANOMA

A CASE OF ANORECTAL c-kit POSITIVE AMELANOTIC MELANOMA

症例は79歳,女性. 2004年10月排便時下血を主訴に来院.直腸診で1～4時方向に直径約5cmの隆起性病変を触知.注腸像ではRbに陰影欠損を認め, CTでは直腸左壁に直腸壁とisodensityの腫瘤を認めた.大腸内視鏡では1/4周性の1型腫瘍を認めた.肉眼的に黒色の部分は認めず,生検では低分化腺癌であった.直腸癌の診断で2004年12月腹会陰式直腸切断術を施行した.病理組織学的所見はa1, n1(+), P0, H0, M(-) stage IIIaであった.免疫組織染色を施行したところHMB-45・S-100が陽性で,メラニン色素はわずかに陽性の肉眼的無色素性悪性黒色腫であった.直腸無色素性悪性黒色腫は予後不良の稀な疾患で,消化管間質腫瘍では鑑別診断として念頭に置く必要がある.また本症例ではc-kitが陽性であったが,このことはc-kitがGISTに特異的ではなく,悪性黒色腫や他疾患でも陽性になり得ることも念頭に置く必要があると思われた.

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