LETTERS TO THE EDITOR

 

Primary anorectal malignant melanoma: an uncommon anorectal pathology

 

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Key words: Melanoma. Primary anorectal melanoma. Abdominoperineal resection. Wide local resection.

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Dear Editor,

Anorectal malignant melanoma (AMM) is the most common primary melanoma of the gastrointestinal tract, accounting for 0.05% and 1% of all colorectal and anal cancers.

 

Case Report

We report the case of an 85 year-old woman with no significant past medical history who presented two-month period of rectal bleeding, abdominal pain, tenesmus and 2 kg weight-loss. Laboratory markers were unremarkable, although rectal examination revealed two small haemorrhoids and a firm, non-obstructing mass in the lower rectum. Colonoscopy confirmed presence of an ulcerated pigmented neoplasm arising at dental line (Fig. 1 A and B). No distant metastases were found on computed tomography (Fig. 1C) although metastatic regional lymph nodes on pelvic MRI were observed (Fig. 1D). Therefore, abdominoperineal resection was performed, confirming loco-regional disease. Histopathology showed malignant melanoma with positive stains in immunohistochemistry for protein S100, HMB-45 and melan-A (Fig. 1 E and F) and stained negative for c-Kit.

 

 

Discussion

Melanoma arises from every location where melanocytes are present (skin, mucosal epithelium). The majority arises in the skin, while primary mucosal location is rare, carries worse prognosis and accounts for only 1%. Head-neck (55%), anorectal (24%) and vulvovaginal (18%) mucosa are the most frequent sites (1). Prevalence is higher among Caucasian females and it is frequently found within 6 cm of the anal rim: rectum (42%), anal canal (33%) or both (2). Symptoms are non-specific. AMM is often identified as an incidental finding on the evaluation of anorectal pathology. Histological misdiagnosis is frequent as melanin pigment is present in only 30%. Therefore, immunohistochemistry panels can be useful: anti S-100 protein, HMB-45 and melan-A (3). The 5-year survival rate has been reported to be less than 20% with variable median survival. Surgical approach seems to be the only curative treatment, as radio and chemotherapy do not really improve survival. Wide local excision and abdominoperineal resection are accepted, although no one has demonstrated survival advantage.

 

José Francisco Juanmartiñena^1,2, Iñaki Fernández-Urien^1,2 and Alicia Córdoba3
Departments of ¹Endoscopy, ²Digestive Diseases and
³Pathology. Complejo Hospitalario de Navarra. Pamplona, Navarra, Spain

 

References

1. Fernández M, Irarrázaval J, Larach A, et al. Melanoma anorrectal asociado a metástasis colónicas. Rev Esp Enferm Dig 2014;106:281-2.         [ Links ]

2. Zhang S, Gao F, Wan D. Effect of misdiagnosis on the prognosis of anorectal malignant melanoma. J Cancer Res Clin Oncol 2010;136:1401-5. DOI: 10.1007/s00432-010-0793-z.         [ Links ]

3. Duarte P, Ramos R, Vicente C, et al. Anal melanoma with satellite implantations on the lower rectum. Rev Esp Enferm Dig 2011;103:49-51. DOI: 10.4321/S1130-01082011000100016.         [ Links ]