Anorectal Melanoma Diagnosed on Index Colonoscopy

CASE REPORT A 61-year-old woman presented with 2 months of scant rectal bleeding and a painful anal lump. Digital rectal examination noted a fungating mass protruding through her anus without pigmentation changes. Colonoscopy revealed an ulcerated, necrotic mass in the anorectal canal, best viewed in retroflexion. Biopsies were consistent with melanoma (Figure 1). Positron emission tomography-computed tomography detected a 4 cm anorectal mass without regional adenopathy or metastases. After multidisciplinary consultations, the patient opted for a nonoperative approach and underwent radiotherapy with nivolumab immunotherapy. Her disease was deemed incurable after follow-up imaging noted metastasis.Figure 1.: (A) Retroflexed view of fungating anorectal mass. (B) Scant benign rectal mucosa on the left, with the poorly differentiated spindle cell malignancy to the right (objective 10×). (C) Immunohistochemistry of SOX10: tumor cells stain strongly and diffusely positive (objective 10×).Anorectal melanoma is rare, accounting for 1% of anorectal malignant tumors and 1.6% of melanomas, and is typically found in female patients older than 50 years presenting with symptoms of rectal bleeding, pain, or itching.1,2 These tumors are aggressive with a poor prognosis given difficulty in early detection based on hidden location and absence of early symptoms, with a 5-year survival rate of 10%-15%.1,2 Surgery is often considered, but does not improve overall survival, and there is no consensus regarding surgical or medical management.2 We present a case of malignant melanoma detected on colonoscopy and highlight the importance of digital rectal examination and endoscopic retroflexion in the workup of anorectal symptoms. DISCLOSURES Author contributions: CG Angelo: provided substantial contributions, drafted the manuscript, amended the manuscript, participated in final approval, and is the article guarantor. SM Malik: assisted with gathering information for the manuscript, critically reviewed the drafted manuscript, participated in final approval process. ED Nellis: provided substantial contributions, critically reviewed the manuscript and revisions, contributed to final approval of the manuscript. Financial disclosure: None to report. Informed consent was obtained for this case report.