Congenital epulis and granular cell tumor: a histologic and immunohistochemical study

Although it is now reasonably certain that granular cell tumors derive from Schwann cells, the histogenesis of congenital epulis, which is largely isomorphic with granular cell tumor, remains unclear. A study was undertaken to compare the immunophenotype of these tumors with particular emphasis on the expression of matrix proteins and macrophage markers because such information is not available in the literature.

Four granular cell tumors and two congenital epulis were immunostained with a panel of 29 antibodies. Two congenital epulis and one granular cell tumor were investigated by electron microscopy, the latter also by immunoelectron microscopy.

Many similarities in immunostaining were found, for example, both tumor types were CD68+, Ki-M1P+, lysozyme-, vimentin+, fibronectin+, laminin+, lectin PHAE+, and lectin WGA+. However, differences were also noted, for example, granular cell tumor was always S100 protein+, but only one congenital epulis case was reactive (weak reactivity after microwave treatment), and staining with the proliferation markers anti-proliferating cell nuclear antigen and MIB 1 was found only in congenital epulis. Both tumor types exhibited pericellular and diffuse cytoplasmic staining for fibronectin and laminin.

The hypothesis that congenital epulis and granular cell tumor would exhibit similar reactivity for macrophage markers was confirmed: both were reactive with anti-CD68 and Ki-M1P and nonreactive with MAC387, anti-lysozyme, and 3A5. Intracytoplasmic staining for fibronectin and laminin, which has not been described previously in these tumors, appears to be a characteristic feature common to both tumors. This finding suggests that there could be a disturbance of synthesis and secretion of extracellular matrix proteins or a derangement of their receptor systems. This theory could be supported by the finding of intracytoplasmic CD49e-positive material in two cases.