The cells mainly show the immunohistochemical features of conventional melanoma cells (S-100, HMB45, melan-A expression) (Fig. 50.3). Although it is generally believed that balloon melanoma cells represent a degenerative change, the immunohistochemical and electron microscopic findings suggest that the balloon tumor cells are most likely metabolically active melanocytic cells. In particular, electron microscopy shows abundant cytoplasmic membrane-bound vacuoles, few or no melanosomes, and only infrequent abnormal premelanosomes.

Balloon cells are usually sparse in the primary melanoma but have a potential of constituting the entire lesion in metastasis. In few cases, the metastasis of melanoma is composed of balloon cells, whereas the primary melanoma does not exhibit any balloon cells and predominantly consists of spindle-shaped and epithelioid cells.

A peculiarity of BCMM is the general lack of melanin, in contrast to conventional melanoma and balloon nevus cells.