A CASE OF ANORECTAL c-kit POSITIVE AMELANOTIC MELANOMA

• Published in: Nihon Rinsho Geka Gakkai Zasshi (Journal of Japan Surgical Association) Vol. 67; no. 4; pp. 851 - 855
• Main Authors: NAGASHIMA, Takuya, SHIRAISHI, Ryuuji, KATAYAMA, Kiyohumi, TANI, Kazuyuki, KUMAMOTO, Yoshikazu, TANABE, Hiroyasu
• Format: Journal Article
• Language: English
• Published: Japan Surgical Association 2006
• Subjects: c-kit
• ISSN: 1345-2843; 1882-5133
• DOI: 10.3919/jjsa.67.851

We report a case of anorectal amelanotic malignant melanoma which stained positive for c-kit. A 79-year-old woman was admitted to our hospital because of anal bleeding at defecation in October 2004. During digital examination of the rectum, a large soft tumor about 5cm in diameter was palpated. Barium enema showed a filling defect in the lower rectum. Abdominal CT scan showed an isodensity mass at the left wall of the rectum. Colonoscopy showed a quarter-circled type 1 tumor. Grossly no pigmentation of the tumor was recognized, and pathological examination of the biopsy specimen indicated a diagnosis of poorly differentiated adenocarcinoma. Abdominoperineal resection was performed with the preoperative diagnosis of rectal carcinoma in December 2004. Microscopically, the tumor cells reacted positively to immunohistological staining with HMB-45 and S-100. Melanin pigment was seen after Fontana-Masson staining in only a few tumor cells. The final pathological diagnosis was amelanotic malignant melanoma. Amelanotic malignant melanoma is a rare entity and has a poor prognosis. We should recognize this disease as a differential diagnosis for interstitial tumors. We must keep in mind as well that the c-kit staining is not specific for GIST and can give positive reactions to melanoma and other disease.