Primary malignant melanoma with surrounding melanosis in the anorectum.

emergency room with hematochezia. Apart from a low hemoglobin level (8.9 g/dL), laboratory findings were unremarkable. On colonoscopy, a large mass with a dark-stained surface was observed extending from the anus up to 3 cm above the anal verge (●" Fig. 1). When the mass was examined after retroflexion, it was noted that the ulcerating mass itself was surrounded by black pigmented mucosa (●" Fig. 2). Biopsy samples were taken from both the darkly stained mass and the pigmented mucosa. Histologic examination of the mass showed neoplastic cells with black pigmentation, which proved to be malignant melanocytes and were positive for HMB45 andMelan-A on immunohistochemical staining. The surrounding pigmented mucosa was shown to be simple melanosis (●" Fig. 3). In order to exclude the possibility of the mass being a metastatic lesion rather than a primary lesion, a thorough physical examination and imaging studies were carried out. There was no evidence of any other primary lesions or distant metastases. Therefore the anorectal mass was diagnosed to be primarymelanoma. The patient underwent abdominoperineal resection (●" Fig. 4), and the histologic report was consistent with the previous findings: primary malignant melanoma surrounded by black pigmented mucosa. The patient is currently on chemotherapy. Primary melanoma most frequently occurs in the skin and retina but it can also occur in the gastrointestinal tract, which is the third most common site. However, anorectal malignant melanoma is a rare neoplasm and has a poor prognosis [1]. It is important to rule out the possibility of the lesion being a metastasis rather than a primary focus. Although controversy still exists about the most appropriate therapeutic strategies, surgical excision remains the mainstay of treatment [2]. Adjuvant chemotherapy and radiation therapy have not been proved to have a significant role in increasing survival.