Anorectal balloon cell melanoma: a rare variant

Abstract

Balloon cell melanoma is a rare presentation of malignant melanoma, usually on the skin, with less than 100 cases reported. Mucosal BCM is even rarer, with only one case of anorectal BCM reported in English literature. The diagnosis is based on the histopathologic findings of a tumor composed of large, foamy melanocytes, with or without pigmentation, and confirmed by immunohistochemical studies showing expression for melanocytic markers. The foam cell appearance of the tumor cells and the lack of melanin pigment lead to a diagnostic dilemma, mostly when presented at an unusual location. Herein, we report a case of balloon cell melanoma at the anorectal junction in a 73-year-old male patient complaining of constipation and bleeding per rectum. Surgical resection was performed with no evidence of recurrence after three years of close follow-up. We believe this case will raise awareness among the medical community to consider this tumor a differential diagnosis in rectal masses.

Keywords: Abdomen; Balloon Cell Melanoma; Immunohistochemistry; Rectal neoplasms.

Figure 1. Photomicrograph of the polypoid lesion showing in A and B – unremarkable anal mucosa with underlying tumor disposed in sheets of epithelioid and balloon cells having abundant eosinophilic to vacuolated cytoplasm with central to eccentric hyperchromatic nucleoli; C – shows overlying rectal mucosa with subepithelial zone infiltrated by tumor. (H&E, A – 100X, B – 200X, C – 100x)

Figure 2. Immunohistochemical findings: A – Tumor showing diffuse expression for S-100, B – HMB-45, C – Melan A, negative expression for D – Ki 67 proliferation index. (Original magnification, A-D DAB 200x)