Perineurial cells in granular cell tumors and neoplasms with perineural invasion: an immunohistochemical study

Granular cell tumors (GCT) are nerve sheath neoplasms composed of Schwann cells with granular cytoplasm. Perineurial cells are the cellular component of the perineurium and of perineuriomas, neoplasms supposedly derived from perineurial cells. However, perineurial cells have also been found in other Schwann cell-derived tumors. These cells have not been well studied in GCTs. We studied the presence of perineurial cells in a series of 24 GCTs with EMA, claudin-1, and Glut-1, which are immunohistochemical markers for perineurial cells. Three cases lacked nerve fascicles. Three cases showed no perineurial proliferation (grade 0), 7 showed grade 1 proliferation, and 11 showed grade 2 proliferation. For comparison, we studied 17 cases of neoplasms with perineural invasion (PNI): 7 cutaneous neoplasms [squamous cell carcinomas (n = 3), cutaneous lymphoma, malignant melanoma, eccrine carcinoma, congenital neurotropic nevus (n = 1 each)] and 10 noncutaneous tumors [prostatic (n = 2), gastric (n = 2), and colonic (n = 2) adenocarcinomas; invasive ductal carcinoma of breast (n = 2); urothelial carcinoma of bladder (n = 1); and oral squamous cell carcinoma (n = 1)] with the same antibodies for perineurial cells. We found perineurial cell proliferation in 10 cases, 6 grade 1, and 4 grade 2. These perineurial cells were limited to the areas around the nerve fascicles. Most of the tumor was devoid of perineurial cells. Thus, it was interpreted more as a hyperplastic or reactive phenomenon than a neoplastic component. Claudin-1 was the most sensitive of the 3 markers that we used. Such proliferation was less intense in non-GCTs. In conclusion, proliferation of perineurial cells in GCTs and neoplasms with PNI is a common finding that had not been previously studied. It seems to be a non-neoplastic phenomenon.