Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems

Summary Four melanin pigment-containing intracranial tumors were found in three Long-Evans rats in the course of experimental oncogenesis by transplacental ethylnitrosourea (ENU). One of them was a leptomeningeal melanoma. Aside from the presence of scattered melanin-pigmented cells, the other three had the typical histological features of ENU-induced malignant nerve sheath tumors. Two of the three tumors were studied by electron microscopy and in tissue and organ culture systems. One of them demonstrated progressive melanogenesis in vitro; the other failed to produce more melanin and showed increasing differentiation, with a Schwannoma-like pattern by light microscopy. Melanosomes and premelanosomes were identified in both tumors by electron microscopy; the other fine structural features were those of malignant Schwannomas.These observations are relevant to the controversy on the histogenesis of pigmented nerve sheath tumors occasionally encountered in man and on the relationship of these tumors to pigmented nevi. The findings in the present study support the view of Masson that neoplastic nerve sheath cells are capable of melanogenesis.Supported by Research Grant CA 11689 from the National Cancer Institute, Graduate Neuropathology Training Grant 5 T01 NS 5500-09 and by Special Fellowships 1F03 NS 55632 (A.M.S.) and 1F11 NS 2629 (F.K.C.) from the National Institute of Neurological Diseases and Stroke, U.S.P.H.S.