Proliferative activity, angiogenesis, and necrosis in peripheral nerve sheath tumors: a quantitative evaluation for prognosis.

Malignant peripheral nerve sheath tumors (MPNSTs) are distinguished from a control group of typical benign schwannomas and neurofibromas on the basis of a set of quantitatively evaluated parameters, i.e., the cell density; the number of mitoses and apoptotic bodies; the nuclear area and shape; the number and absolute and relative areas of silver-staining nucleolar organizer regions; necrosis; and angiogenesis. Only the extent of tumor necrosis, the mitotic rate, and the parameters related to silver-staining nucleolar organizer regions discriminate between less aggressive MPNSTs (disease-free patients after 4 years of follow-up) and more aggressive MPNSTs (with recurrences or metastases during the first 4 years of follow-up).