Interaction of Histologic Subtype and Histologic Grade in Predicting Survival for Soft-Tissue Sarcomas

Background: Histologic grade is considered the paramount prognostic factor in predicting survival for soft-tissue sarcomas (STS). Increasing data suggest that histologic type substantially impacts STS behavior. Study Design: The Surveillance, Epidemiology, and End Results program was used to identify 17,364 cases of STS diagnosed between 1988 and 2004. Using death from STS as 1 of the outcomes variables, histologic types were grouped into 3 categories: favorable (survival ≥ 20% above the mean), neutral (survival within 20% of the mean), and unfavorable (survival ≥ 20% below the mean). The effect of histology on survival was analyzed stratified by tumor grade. Five-year survival was calculated using Kaplan-Meier analysis. Results: Among 73 histologic types, malignant fibrous histiocytoma (24.1%); leiomyosarcoma, not otherwise specified (14.8%); sarcoma, not otherwise specified (12.8%); and myxoid liposarcoma (5.9%) were the most prevalent. Grade distribution was as follows: low, 12.6%; intermediate, 14.9%; high, 37.1%; and unknown, 35.4%. Risk of death from STS increased with increasing grade: 8.0% for low, 25.9% for intermediate, and 38.3% for high. Among low-grade tumors, risk of death from STS ranged from 4.3% for favorable types to 15.3% for unfavorable types. Among intermediate-grade tumors, risk of death from STS ranged from 6.0% for favorable types to 45.4% for unfavorable types. Among high-grade tumors, risk of death from STS ranged from 24.3% for favorable types to 58.9% for unfavorable types. Conclusions: Within categories of STS grade, there are substantial differences in survival, depending on histologic type. Histologic type is an important predictor of biologic behavior in STS.