P0826 - Comparative outcomes between osteosarcoma and pediatric soft tissue sarcomas of bone: a National Cancer Database analysis

Introduction
Osteosarcoma is the most common primary malignancy of bone in children. The rarity of pediatric soft tissue sarcomas has complicated large-scale analyses. Herein we describe characteristics of pediatric patients with osteosarcoma or other primary bone sarcomas and treatment outcomes from the National Cancer Database (NCDB).

Methods
The NCDB was queried from 2004-2014 for patients aged 0-17 years with primary malignant sarcomas of bone. Exclusion criteria included tumors involving the bones of the skull or mandible, surface or periosteal lesions, Ewing’s sarcoma, desmoplastic round cell sarcoma, chondrosarcoma, small cell sarcoma, clear cell sarcoma, adamantinoma, rhabdomyosarcoma, carcinosarcoma, infantile fibrosarcoma, and giant cell tumor. Tumors of unspecified tissue origin were also excluded. Patients were divided into osteosarcoma and rare bone sarcomas. Survival was analyzed with Kaplan-Meier curves and compared using log-rank tests. Factors predictive of survival were analyzed with multivariate Cox proportionate hazards models. Demographic, tumor characteristic, and treatment variable were analyzed using Chi-squared and Mann-Whitney tests.

Results
2621 osteosarcoma and 100 rare bone sarcomas were included. The most common histologic sub-types within the primary bone sarcoma cohort were sarcoma, not otherwise specified (NOS) (31%), synovial sarcoma NOS (12%), and spindle cell sarcoma (11%) (Table 1). Osteosarcoma patients were slightly younger (median=13, IQR=4) than those in the other bone sarcoma cohort (median=14, IQR=3). Males and Caucasians were most commonly affected. The most common primary tumor site across sarcomas was the lower limbs. Osteosarcoma patients had significantly larger and more advanced grade lesions and presented with fewer metastases at diagnosis than rare bone sarcoma patients. Osteosarcoma patients were more likely to be treated sooner and undergo surgery and chemotherapy, but less likely to receive radiotherapy, than other sarcoma patients.
No statistically significant difference in overall survival was observed between osteosarcoma and other bone sarcoma patients. The median survival—defined as time to death or censor—among pediatric osteosarcoma patients was 52.3 months compared to 27.4 months for patients with other bone sarcomas. Primary appendicular tumors yielded superior survival compared to axial site in both cohorts. No apparent survival benefit was observed with chemotherapy, though lack of radiotherapy was associated with greater survival. Among osteosarcoma patients, Cox proportional hazards analysis found that Caucasian race, lack of metastasis at diagnosis, surgical intervention, and telangiectatic osteosarcoma histology significantly improved survival. Tumor size >10 cm and an axial primary tumor site negatively affected survival. With respect to other primary sarcomas of bone, only tumor size >10 cm significantly impacted survival.

Discussion
Pediatric rare bone sarcoma patients share many demographic factors with, but are associated with more negative tumor characteristics than, osteosarcoma patients. Surgery improved, while chemotherapy failed to increase, overall survival. Larger-scale analyses of rare pediatric bone sarcomas are needed to more thoroughly investigate these trends.