Cutaneous clear-cell granular cell tumors: the histologic description of an unusual variant.

Background: Granular cell tumors (GCTs) are neoplasms showing nerve sheath differentiation that can arise in the skin but, to our knowledge, have not been associated with significant clear-cell morphology.

Methods: Two patients developed four separate GCTs with distinctive, diffuse clear-cell change, which completely camouflaged the primary differentiation. The morphology, histochemistry and immunohistochemistry of the lesions are described and are compared with the presence and extent of clear-cell change in 14 other cases of GCTs.

Results: The index cases were relatively broad proliferations with uniform diffuse clear-cell change and only minimal overlying epidermal hyperplasia. Prominent lymphoid nodules were present at the periphery. These clear-cell granular tumors were positive for S-100 protein, p75, CD68, NKI/C3 and neuron-specific enolase and were negative for epithelial mucin, periodic acid-Schiff, carcinoembryonic antigen, HMB-45, Melan-A, smooth muscle actin, Leu7, synaptophysin, CD34, factor XIIIa, epithelial membrane antigen and cytokeratin. Three of the fourteen comparison cases were found to have no clear-cell change, eight showed focal clear-cell change and three showed moderate clear-cell change.

Conclusions: The distinctive morphology and the immunohistochemical results are discussed in the context of the differential diagnosis of clear-cell cutaneous tumors.