Optimal Percent Myxoid Component to Predict Outcome in High-Grade Myxofibrosarcoma and Undifferentiated Pleomorphic Sarcoma

Background. Myxofibrosarcoma and undifferentiated pleomorphic sarcoma (UPS) are aggressive, genetically complex sarcomas. The minimum myxoid component used as a criterion for myxofibrosarcoma varies widely, so we determined the optimal myxoid component cutpoints for stratifying outcomes of UPS and myxofibrosarcoma. We also analyzed clinicopathologic factors associated with outcome. Methods. Review of a prospective, single-institution database identified 197 patients with primary, high-grade extremity/truncal myxofibrosarcoma or UPS resected during 1992-2013. Histology was reviewed and percent myxoid component determined for each tumor. Disease-specific survival (DSS) and distant recurrence-free survival (DRFS) were analyzed using the Kaplan-Meier method, log-rank test, and Cox regression. Results. Median follow-up for survivors was 6.4 years. In minimum p value analysis of myxoid component, the best cutpoint for both DSS and DRFS was 5 % (adjusted p <= 0.001), followed by 70 %. Therefore, sarcomas with <5 % myxoid component (n = 69) were classified as UPS and those with >= 5 % myxoid component (n = 128) as myxofibrosarcoma. Five-year DRFS was 24 % for UPS, 51 % for 5-69 % myxoid component myxofibrosarcoma, and 65 % for >= 70 % myxoid component myxofibrosarcoma. Myxoid component, tumor size, and age were independently associated with DSS; myxoid component and tumor size were associated with DRFS. Only tumor site was associated with local recurrence. Conclusions. Percent myxoid component and tumor size are the two most important predictors of DSS and DRFS in high-grade myxofibrosarcoma and UPS. A 5 % myxoid component cutpoint is an improved criterion for classifying myxofibrosarcoma. Myxoid component-based classification improves stratification of patient outcome and will aid in selection of patients for systemic therapy and clinical trials.