© Georg Thieme Verlag KG Stuttgart · New York
Primary malignant melanoma with surrounding melanosis in the anorectum
15 February 2010 (online)
A 76-year-old woman presented to the 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]).
Fig. 1 Colonoscopy showing a large, dark-stained mass extending from the anus up to 3 cm above the anal verge on forward view.
When the mass was examined after retroflexion, it was noted that the ulcerating mass itself was surrounded by black pigmented mucosa ([Fig. 2]).
Fig. 2 The ulcerating mass surrounded by black pigmented mucosa on retroflexed view.
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 HMB-45 and Melan-A on immunohistochemical staining. The surrounding pigmented mucosa was shown to be simple melanosis ([Fig. 3]).
Fig. 3 Histologic section showing neoplastic cells (left) that proved to be malignant melanocytes and stained positive for HMB-45 (right).
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 primary melanoma. 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.
Fig. 4 The resection specimen showing a well-demarcated ulcerofungating mass, measuring 4 × 3.4 cm. A diffuse dark-grayish discolored area is surrounding the mass.
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 . 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 . Adjuvant chemotherapy and radiation therapy have not been proved to have a significant role in increasing survival.
- 1 Weinstock M A. Epidemiology and prognosis of anorectal melanoma. Gastroenterology. 1993; 104 174-178
- 2 Bullard K M, Tuttle T M, Rothenberger D A. et al . Surgical therapy for anorectal melanoma. J Am Coll Surg. 2003; 196 206-211
B. Keum, MD, PhD
Department of Internal Medicine, Institute of Digestive Disease and Nutrition, Korea University College of Medicine, Seoul