A Rare Case of Primary Anorectal Melanoma and a Review of the Current Landscape of Therapy

Abstract

Introduction: Anorectal mucosal melanoma (ARMM) is an uncommon and highly aggressive malignancy. Given its rarity, there is insufficient evidence on the optimal medical management which presents as a clinical challenge to its diagnosis and treatment. Treatment of ARMM typically involves a multimodal approach including surgical resection, chemotherapy, targeted therapy and/or immunotherapy. Case Presentation: Here, we present a case of a 78-year-old female who presented with a four-month history of rectal bleeding and bowel incontinence. Ultimately, colonoscopy revealed a mass at the anal verge, and biopsy of the mass showed malignant cells that stained positive for S100, Melan-A and HMB-45, consistent with the diagnosis of malignant melanoma. Molecular testing revealed no BRAF, KIT or NRAS gene mutations. PD-L1 immunohistochemistry showed tumor proportion score of 1%. She underwent abdominoperineal resection with a plan to initiate immunotherapy with an anti-PD-1 checkpoint inhibitor. This case highlights a rare aggressive malignancy and reviews its treatment option, which are mostly extrapolated from its cutaneous counterpart and some derived from a few case reports. Due to its rarity, there is no consensus guideline for the treatment of ARMM.

Debulking Operation, Radiation Therapy, and Sphincter-Sparing Local Wide Excision for The Lower Rectal Melanoma: A Case Report

“…In summary, no consensus exists on rectal melanoma treatment. In addition to traditional surgery and RT, immunotherapy is recently developing as an option [29,30]. In conclusion, the current study presented a case with stage II rectal melanoma with a complete response by combining debulking surgery, RT, and WLE.…”

Surgical treatment of anorectal melanoma: a systematic review and meta-analysis

“…In addition, it suggests the need for newer treatment modalities like immunotherapy and targeted therapies. Although cutaneous melanomas are found to be highly immunogenic, this has not been shown yet for anorectal or other mucosal melanomas 82 . This suggests mucosal melanomas might have a different aetiology and that further investigations on this subject are necessary.…”

A Rare Case of Primary Anorectal Malignant Melanoma

“…The anal canal is the most common site of malignant melanoma in the gastrointestinal tract because melanocytes are commonly found in the anal squamous epithelium. ARMM accounts for less than one percent of rectal tumors [ 1 ]. These tumors are more common in females than males and are usually seen after 60 years.…”

“…Malignant melanoma affecting the gastrointestinal tract is very rare, and the anorectum is the most common site being affected. Anorectal malignant melanoma (ARMM) accounts for less than one percent of colorectal malignancies [ 1 ]. The exact etiology of the disease is not known.…”