Malignant Melanoma of Anorectum: A Report of Five Cases

Abstract

BACKGROUND: Anorectal melanoma (ARM) is an extremely rare, highly aggressive form of a tumor with the worst prognosis. ARM contributes 0.5% of all melanoma cases^.  Its presentation is similar to that of adenocarcinoma of the rectum, hemorrhoids, or solitary rectal ulcer, the incorrect clinical diagnosis or delayed diagnosis is often made. The definite diagnosis is only made through histopathology in which immunohistochemical stains positive to S-100, Melan A, and HMB-45 which differentiates it from adenocarcinoma of the rectum.

Because of the limited number of patients and retrospective design of studies to date, there is no proven efficacy of abdominoperineal resection (APR) over local excision (LE) in terms of survival. Furthermore, this neoplasm is quite resistant to chemoradiotherapy. It has a median survival of 18 months and a 5-year survival rate of only 6%.

PRESENTATION OF OUR CASES: Here, we report 5 rare cases of anorectal malignant melanoma presented to our institute between 2018 to 2022, who were treated with APR and diversion colostomy. The first case is a 27-years old young female with typical complaints, she was diagnosed ARM with locoregional metastasis. Only a diversion colostomy was performed and referred to an oncologist for palliation. Our second case is a 68-years old male with a similar complaint who presented relatively early and was diagnosed with localized disease. Conventional APR was performed and referred for adjuvant chemoradiotherapy, but the patient refused. However, the lump recurred after 6 months of tumor excision. The third case is a 29 years old male again early presentation with a similar complaint labeled as localized diseased. The conventional APR was performed followed by adjuvant chemoradiation; patient presented with metastatic disease after 6 months. The fourth case is a 60-years old male with typical history and diagnosed with localized disease. Conventional Extra-levator APR was performed followed by adjuvant therapy, but patient developed recurrence of disease with mets after 4 months. The fifth case is a 39-years old female diagnosed as ARM, had advance disease and metastatic deposits at the time of presentation, refused any palliative treatment. The study aims to evaluate our experience in treating this neoplasm.

CONCLUSION: Because of the rarity of this neoplasm, no proper trial has been conducted so far. The role of chemoradiotherapy is questionable and the surgical approach varies from radical APR to conservative LE.  No surgical approach has been standardized in terms of survival.