Anorectal melanoma: A case report of an unusual localization

Abstract

INTRODUCTION AND IMPORTANCE: Primary anorectal melanoma (ARM) is a rare neoplasm with an extremely poor prognosis. It represents less than 1 % of all melanomas and accounts for less than 1 % of anorectal malignancies. We report a case of anorectal primary melanoma treated surgically. CASE PRESENTATION: A 73-year-old presented with a rectal syndrome evolving over 3 months, associated with rectal bleeding and sub-occlusive syndromes progressing in the context of general deterioration. Anal margin examination showed a protruding lesion with blackish color of the anal mucosa. Biopsies with histopathological examination concluded a malignant melanoma with necrotic changes. Locoregional staging with thoracic-abdominal-pelvic CT scan revealed a suspicious thickening of the rectum's lower wall contacting the posterior wall of the vagina, with loss of fat stranding associated with multiple mesorectal lymph nodes without distant secondary lesions. A laparoscopic proctectomy was performed. A histopathological examination of the specimen confirmed the diagnosis with clean margins. The patient recovered uneventfully. DISCUSSION: Anorectal melanoma is an exceedingly rare form of cancer, comprising less than 1 % of all anorectal malignancies. Surgical intervention remains the primary treatment modality for anorectal melanoma. Abdominoperineal resection has traditionally been the mainstay approach. Studies have suggested that localized excision coupled with adjuvant therapies such as low-dose radiotherapy may offer comparable local control rates to traditional abdominopelvic resection while preserving sphincter function and quality of life. CONCLUSION: Anorectal melanoma is a rare disease with poor prognosis. The lack of high-volume data researches shows the missing guideline for this disease.