Prognostic factors of myxofibrosarcomas: Implications of margin status, tumor necrosis, and mitotic rate on survival

Background: Myxofibrosarcomas (MFS) are characterized by tumor progression with increased metastases after local recurrences (LR). Few series had appropriately addressed what parameters independently affect prognosis. Methods: Seventy primary localized MFS were analyzed for local recurrence-free survival (LRFS), metastasis-free survival (MeFS), and disease-specific survival (DSS). Follow-up was obtained in 61 cases. Results: Thirty-eight males and 32 females had primary tumors ranging from 1.5 to 24 cm. Thirty and 40 tumors were superficial and deep, respectively, with 26 cases (38%) having positive margins. The 5-year LRFS-, MeFS-, and DSS-rates were 30%, 60%, and 73%. Positive margins (P = 0.0003) were the only inferior LRFS predictor. High grade (FNCLCC 2 and 3) was a negative factor of both MeFS (P=0.0078) and DSS (P=0.0174), and high stage (AJCC stage 3) was predictive of MeFS (P=0.0470). However, both grading and staging were not prognostically independent. In multivariate analyses, mitoses >= 20/10 HPF (P=0.0009, RR=9.71) and positive margins (P = 0.0203, RR = 4.27) were independent adverse DSS predictor. However, tumor necrosis >= 10% (P = 0.0092, RR = 3.91) independently correlated with worse MeFS, together with mitoses >= 20/ 10 HPF (P = 0.0 176, RR = 3.80) and positive margins (P = 0.0 121, RR = 3.41). Conclusions: Margin status and histologic property both affect the prognosis of MFS. The former correlates with improved LRFS and translates into final survival benefits.