Abstract

Balloon cell melanoma (BCM) is a rare histological variant of malignant melanoma characterized by large melanocytes with abundant clear, foamy, or vacuolated cytoplasm (1). Less than 100 cases have been described in the literature, with a mean age of presentation of 57 years according to a recent systematic review. Approximately half of the reported cases represent metastatic BCMs, and in a small subset of the patients enlarged lymph nodes are the initial clinical presentation (2). Herein, we report a 50-year-old female who presented with multiple enlarged right axillary lymph nodes, including a matted lymph node 8 cm in greatest dimension. Histological examination revealed a large tumor in association with lymphoid tissue in the matted lymph node. The neoplastic cells exhibited an unusual cytomorphology with abundant clear to foamy cytoplasm, resembling foamy histiocytes on low magnification. High-power examination showed significant nuclear pleomorphism, prominent nucleoli, brisk mitotic activity, and tumor necrosis. The tumor cells were positive for S-100, Melan-A, HMB45, and SOX10. On assessment of the other lymph nodes with immunohistochemical stains, isolated tumor cells were identified within lymphatic channels and lymph node parenchyma. On H&E-stained slides, however, these cells were not easily discernible due to their cytomorphology. The patient was lost to follow-up. This case represents a rare example of a metastatic BCM involving the axillary lymph nodes, initially presenting with lymphadenopathy. This entity has the potential to pose a diagnostic challenge, especially when it presents as isolated tumor cells and without a known primary. 1) Chavez-Alvarez S, Villarreal-Martinez A, Miranda-Maldonado I, Ocampo-Candiani J, Garza-Rodriguez V. Balloon cell melanoma and its metastasis, a rare entity. Am J Dermatopathol 2017;39:404-11. 2) Wei G, Hennessy K, Kevin Heard L, et al. Balloon cell melanoma: a systematic review. Int J Dermatol 2022;61:266-77.

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