Neurogenic tumors of the skin.

A classification of peripheral nerve sheath tumors in the skin is based on analysis of light-, electron microscopy, immunohistochemistry and cellular composition of the different tumor types. Not only Schwann cells, but also perineurial cells and fibroblasts may be involved in tumor formation. Schwann cell rich and connective tissue cell rich tumors are distinguished. Generally all tumors show low proliferating activity as investigated by H3-Thymidine autoradiography. Only in few connective tissue cell rich tumors higher labelling indices can be demonstrated. These findings are correlated with the clinical course and prognosis of the different tumor types. The question remains, whether connective tissue cell rich tumors are at higher risk for malignant transformation.