Interaction of histologic subtype and histologic grade in predicting survival for soft-tissue sarcomas

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.

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 >or= 20% above the mean), neutral (survival within 20% of the mean), and unfavorable (survival >or= 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.

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.

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.