Background: Malignant peripheral nerve sheath tumor (MPNST) is a relatively rare soft tissue tumor, and its clinical relevance of pathological grades remains obscure. Methods: Fifty-six cases of MPNST identified from the files of seven oncology centers of the Tohoku Musculoskeletal Tumor Society (TMTS) and National Cancer Center were analyzed for histologic grades, demographics, treatments, and prognostic factors. The average follow-up period was 41 months. Results: Twenty-two men and 34 women with a mean age of 45 years were involved. Forty-four (78.6%) of 56 tumors were in the lower extremity or trunk. Fifty tumors (89%) were classified as high grade, and the remaining six as low grade. Twenty-one (39.6%) of 53 patients who underwent tumor excision developed local recurrences. An axial site and inadequate surgical margin were defined as risk factors for local recurrence. The overall survival rates of the 56 patients were 55.1% at 3 years and 43.3% at 5 years. Univariate analysis of the 56 patients revealed large-sized tumors, metastasis at presentation, and histologically high grade were significantly associated with poor prognosis. Multivariate analysis revealed a large tumor and metastasis at presentation to be independent prognostic factors. Conclusions: The current study involving 56 patients with MPNST showed the aggressive clinical behavior of the tumor. Large-sized tumors, metastasis at presentation, and high histological grade were related to poor prognosis on univariate analysis, but independency of histological grade was still obscure. In the treatment for a large and high-grade MPNST, an alternative strategy should be further considered.
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