Histopathological features of Malignant Peripheral Nerve Sheath Tumors—MPNSTs. (A,B) Low-grade MPNST composed of a spindle cell proliferation with increased cellularity, mild cytological atypia, few mitoses (3 to 9 mitoses per 10 high-power fields), but no evidence of necrosis (Hematoxylin and Eosin, 200×). Diffuse immunoreactivity for S100-protein is noted (200×). (C,D) High-grade MPNST showing marked hypercellularity, nuclear pleomorphism, necrosis, and numerous mitoses (more than 10 mitoses per 10 high-power fields) (Hematoxylin and Eosin, 200×). Only focal S100-protein positivity is observed.