Non-Rhabdomyosarcoma Soft Tissue Sarcoma (NRSTS) in Pediatric and Young Adult Patients Incidence of cancer ( A ) and soft tissue sarcomas ( B ) in the AYA population. Soft tissue sarcomas, the fifth most common solid tumors in children, are relatively rare and account for about 6-7% of all childhood malignancies. About half of these tumors are rhabdomyosarcomas , and nonrhabdomyosarcoma soft tissue sarcomas (NRSTSs) account for the remainder (ie, about 4% of childhood malignancies). NRSTSs are heterogeneous tumors that have varied biology and histology. The most common types in the pediatric population include fibrosarcoma, synovial cell sarcoma, fibrosarcoma, and malignant peripheral nerve sheath tumor. Other histologic types include hemangiopericytoma, alveolar soft part sarcoma, leiomyosarcoma, liposarcoma , epithelioid sarcoma, and desmoplastic small round cell tumor. Childhood NRSTs are not well studied. Because soft tissue sarcomas are most common in adults, many treatment moda