Metastatic balloon cell malignant melanoma: a case report and literature review.

A case of metastatic balloon cell malignant melanoma (BCMM) is presented. The balloon melanoma cells (BMC) were absent in the shave biopsy of the primary lesion and present as a minor component in the wide and deep excision. A subsequent right neck lymph node metastasis showed complete replacement of the lymph node by large, foamy cells. Though the tumor was amelanocytic and Fontana-Masson stain failed to reveal melanin, it stained positively for S-100, HMB-45, and Melan-A. Ultrastructurally, the foamy cells were characterized by cytoplasmic vacuolization and a lack of melanosomes. The differential diagnosis of metastatic balloon cell malignant melanoma is broad, and clinicopathologic correlation may play a critical role in achieving the correct diagnosis.