Anal Mucinous Adenocarcinoma Presenting as a Superficial Lesion Without Luminal Involvement

Anal mucinous adenocarcinoma arises from mucin-secreting columnar epithelium within anal glands and is extremely rare, comprising 2%-3% of all gastrointestinal malignancies. We present a unique case of 65-year-old developmentally disabled man with complaint of rectal pain. Examination showed an excoriated erythematous perianal region with mucinous film and subdermal nodularity. Surgical pathology of the lesion revealed poorly differentiated mucinous adenocarcinoma of intestinal type. Subsequent colonoscopy was without findings of intraluminal lesions. He established with oncology and later underwent a positron emission tomography scan that showed extensive metastasis. This case highlights a unique presentation of de novo mucinous adenocarcinoma with luminal sparing.