Amelanotic Anorectal Malignant Melanoma In An Ulcerative Colitis Patient: A Rare Coincidence Or A Rare Association

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal system, known to be associated with increased risk of carcinogenesis. We report the case of a 55-year-old woman, presenting with symptoms of increased bowel frequency, per rectal bleeding and rectal pain with a background of ulcerative colitis (UC). This was presumptively managed as UC flare, with titration of her medications to control the symptoms. However, a flexible sigmoidoscopy revealed an ulceroproliferative lesion in the rectum, which was identified as an amelanotic anorectal malignant melanoma on immunohistochemistry. No local or distant metastases were noted on radiological imaging. The tumour enlarged progressively and was managed with laparotomy and defunctioning stoma followed by palliative chemotherapy and immunotherapy. This is the first such case reported in literature, highlighting the importance of endoscopic assessment and the need to consider other differential diagnosis in patients with symptoms of IBD flare.