Difficulties in diagnosing anorectal melanoma: A case report and review of the literature

Abstract

BACKGROUND Anorectal melanoma is a tumour that is difficult to identify due to its rarity and variability of presentation. Insufficient data published in the literature do notallow for diagnostic and treatment guidelines to be established. Anorectalmelanoma has the worst prognosis among mucosal melanomas and is frequentlymisdiagnosed by standard identification methods.CASE SUMMARYA 66-year-old woman presented with intermittent anal bleeding, pain, andtenesmus in the past month, with no associated weight loss. Colonoscopyrevealed a cauliflower-like tumour with a diameter of 1.5 cm, with exulceratedareas and an adherent clot but without obstruction. Biopsy results identified aninflammatory rectal polyp with nonspecific chronic rectitis. Tumour markers CA19-9 and CEA were within the normal range. After 6 mo, due to the persistence ofsymptoms, a pelvic magnetic resonance imaging scan was performed. A lesionmeasuring 2.8 cm × 2.7 cm × 2.1 cm was identified at the anorectal junction, alongwith two adjacent lymphadenopathies. No distant metastases were detected.Immunohistochemistry was performed on the second set of biopsies, and adiagnosis of anorectal melanoma was established. Surgical treatment by abdominoperinealresection was performed. Evolution was marked by the appearance oflung metastases at 1 mo postoperatively, detected on a positron emissiontomography-computer tomography scan, and perineal recurrence after 5 mo.After molecular testing, the patient was included in an immunotherapy trial.CONCLUSIONThis case highlights the difficulty of establishing a definitive early diagnosis ofanorectal melanoma, the importance of performing histological analysis on a wellrepresentedbiopsy specimen, and the poor prognosis, even with radical surgery