Hybrid Epithelioid Schwannoma/Neurofibroma: A Report of 3 Cases.

Peripheral nerve sheath tumors can include neurofibroma, schwannoma, and perineurioma, with hybrid nerve sheath tumor (HNST) being rare. We describe 3 HNST cases with epithelioid schwannoma and neurofibroma features, an uncommon manifestation of hybrid schwannoma/neurofibroma. The 3 cases involved the upper back, forearm, and thigh. Histopathologically, the tumors were located in the subcutis or dermis and subcutis. The epithelioid schwannoma component showed nests/cords of epithelioid cells with round nuclei and abundant cytoplasm. In contrast, the neurofibroma component showed spindle cell proliferation within myxoid stroma. The 3 cases showed variable proportions of both components. Immunohistochemically, the epithelioid schwannoma components were positive for S100 protein and negative for CD34, whereas the neurofibroma component showed partial S100 immunoreactivity and contained abundant CD34-positive cells with a fingerprint pattern. Epithelial membrane antigen and GLUT1 revealed the perineurial capsules. In conclusion, our cases expand the morphologic spectrum of HNST and underscore the importance of recognizing this variant.