Anorectal Melanoma

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This blog is for informational purposes only and should not be taken as medical advice. Content is sourced from third parties, and we do not guarantee accuracy or accept any liability for its use. Always consult a qualified healthcare professional for medical guidance.

What is Anorectal Melanoma?

Anorectal Melanoma is a rare, aggressive mucosal melanoma arising in the anus or rectum, distinct from cutaneous melanoma. It accounts for 1% of melanomas and 0.5% of anorectal cancers, with poor prognosis due to late detection and metastasis. In 2025, it’s managed with surgery and immunotherapy, but outcomes remain challenging.

Symptoms

Symptoms include rectal bleeding, anal pain, mass or lump, changes in bowel habits, tenesmus (feeling of incomplete evacuation), and weight loss. Advanced cases cause pelvic pain, incontinence, or symptoms from metastases (liver, lungs). Symptoms mimic hemorrhoids or colorectal cancer, delaying diagnosis.

Causes

Unlike cutaneous melanoma, UV exposure is not a factor. Causes include genetic mutations (KIT, NRAS more common than BRAF), chronic inflammation, and possibly HPV. Risk factors include older age and immunosuppression. In 2025, studies show mucosal immune responses contribute to aggressive growth.

Diagnosis

Diagnosis involves anoscopy, biopsy with immunohistochemistry (S100, HMB-45 positive), and imaging (MRI, PET) for staging. Molecular testing for KIT/NRAS guides therapy. In 2025, liquid biopsies and AI-assisted endoscopy improve early detection, though most cases present at stage III-IV.

Treatment

Surgery (wide local excision or abdominoperineal resection) is primary, with sphincter-preserving excision preferred for early cases. Immunotherapy (nivolumab, pembrolizumab) achieves 30% response in advanced disease. Targeted therapies (imatinib for KIT mutations) and radiation palliate symptoms. In 2025, combination immunotherapy improves response to 40%.

Future Outlook

In 2025, 5-year survival is 15-20% due to late diagnosis. Immunotherapy and early screening raise survival to 30% in select cases. By 2030, novel KIT inhibitors, oncolytic viruses, and AI-driven diagnostics could achieve 40% survival, with focus on early detection in high-risk groups.

Sources

The information for anorectal melanoma is derived from NCI’s “Melanoma Treatment (PDQ®)” for anorectal melanoma-specific details; PMC’s “Anorectal Melanoma: Clinical and Molecular Features” for causes and diagnostic methods; JAMA Oncology’s “Advances in Mucosal Melanoma Therapy” for 2025 treatment updates; Mayo Clinic’s “Anal Cancer” for overlapping symptom insights; and WebMD’s “Melanoma” for general melanoma context.