Nonrhabdomyosarcomatous soft tissue sarcomas of childhood: formulation of a simplified system for grading.

Because of the rarity of pediatric nonrhabdomyosarcomatous soft tissue sarcomas, it is difficult to test standardized treatment protocols for individual tumor entities. Grading has been used successfully to predict outcome of adult sarcomas, but pediatric soft tissue tumors display a notable difference in clinical behavior when compared to older patients. To test systematically a standardized treatment strategy for pediatric nonrhabdomyosarcomastous soft tissue sarcomas devised by the Pediatric Oncology Group, the authors devised a grading schema using concepts of adult grading systems and integrating the unique clinical and morphologic features of pediatric sarcomas. Three grading tiers were devised: Grade I, which includes certain pediatric tumors with little propensity for malignancy; Grade II, which is composed of tumors excluded from Grades I or III by virtue of histologic diagnosis and having <5 mitoses/10 high-power fields or <15% geographic necrosis; and Grade III, which comprises certain tumors known to be clinically aggressive by virtue of histologic diagnosis and non-Grade I tumors with >4 mitoses/10 high-power fields or > 15% necrosis. An initial retrospective analysis on a series of lesions treated at a single institution indicated a strong predictive value for grading. Subsequent prospective studies by the Pediatric Oncology Group continue to verify the prognostic value of pediatric nonrhabdomyosarcomatous soft tissue sarcoma grading, and studies on individual pediatric nonrhabdomyosarcomatous soft tissue sarcomas, such as synovial sarcoma, also indicate the relatively poor outcome of higher grade lesions. Grade can be used to predict outcome of pediatric nonrhabdomyosarcomatous soft tissue sarcomas and to devise treatment strategies for experimental protocols.