Anorectal Melanoma – Case Report

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Aims

Anorectal melanoma is a rare clinical entity, comprising less than 1% of all colorectal malignancies. Its presenting features are non-specific, leading to frequent missed or delayed diagnoses. Treatment options are limited and generally ineffective, with a median survival of 24 months.

Methods

An 82 year old female presented with a 4 month history of PR bleeding, weight loss and altered bowel habit. Bloods demonstrated a microcytic anaemia, and she had a qFIT >400. A CT colonogram revealed a 7cm x 8cm rectal tumour with potential lymph node involvement. Flexible sigmoidoscopy visualised a large necrotic, ulcerated mass (figure 1). Biopsies were taken and histopathology subsequently demonstrated an immunohistochemical and morphological pattern consistent with a primary anal malignant melanoma. Staging investigations were completed which following the conventional staging approach for other anal
malignancies staged the cancer at T3 N1a M0.

Results

The patient went on to have a laparoscopic defunctioning end colostomy. She recovered well
with an uncomplicated postoperative course. The case was discussed at both colorectal and
dermatology multidisciplinary meetings, which advised oncology referral for planning of
systemic therapy. She is currently awaiting outpatient review by dermatology and oncology.

FIGURE 1. Endoscopic images (A) demonstrating large necrotic mass in rectum.

Conclusion

Anorectal melanomas are a rare but important malignancy. Diagnosis is challenging, and requires
the exclusion of a primary malignant melanoma at another site. Prognosis is poor even in early
stage disease. Treatment generally involves a combination of operative management and
systemic therapy, with some evidence to support the use of targeted therapies such as tyrosine
kinase inhibitors.