VIM and malignant peripheral nerve sheath tumor: The histologic criteria for the diagnosis of malignant schwannoma are based on a combination of the presence of mitotic figures, nuclear atypia, cellularity, and tumor necrosis, and these characteristics may be useful in distinguishing malignant schwannomas from benign.[2] The identification of a neurogenic tumor cell origin is by positive immunostaining for S-100 and vimentin (1–3, 5–8), the characteristic markers of Schwann cells.