title: Osteosarcoma in children 5 years of age or younger at initial diagnosis.
abstract: BACKGROUND
  Since osteosarcoma is extremely rare in children < or =5 years of age, we sought to investigate if tumor characteristics, treatment strategies, and outcomes differ compared to older patients.
  
  
  METHODS
  Patients <20 years of age with high-grade osteosarcoma reported to national SEER database from 1973 to 2006 were separated into two groups based on age at diagnosis: < or =5 years (n = 49) and 6-19 years (n = 1,687). Patient, tumor, and treatment characteristics were compared using Fisher exact tests. Overall survival was estimated by Kaplan-Meier methods and compared using log-rank tests and Cox models.
  
  
  RESULTS
  Patients < or =5 years had higher proportions of osteosarcoma arising from the upper limb compared to older patients (24.5% vs. 11.2%; P = 0.006). These very young patients had a significantly higher proportion of telangiectatic histology (10.2% vs. 2.9%; P = 0.017). Sex, metastatic status, race, or ethnicity did not differ by age. A higher proportion of very young patients was treated with amputation (55.2% vs. 27.3%; P = 0.002). Five-year overall survival was inferior for patients with localized osteosarcoma 5 years of age or younger compared to older children (51.9% vs. 67.3%; P = 0.03). After controlling for metastatic status, year of diagnosis, and tumor site, the hazard ratio for death in very young patients was 1.6 (95% confidence interval 1.02-2.36; P = 0.04) compared to older patients.
  
  
  CONCLUSIONS
  Tumor characteristics, treatment, and outcomes differ among children < or =5 years of age compared to older pediatric patients. These differences may reflect differences in tumor biology.
authors.affiliation: Department of Pediatrics and Department of Epidemiology/Biostatistics, University of California, San Francisco School of Medicine, San Francisco, California, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Worch
authors.forename: Katherine K
authors.initials: KK
authors.lastname: Matthay
authors.forename: John
authors.initials: J
authors.lastname: Neuhaus
authors.forename: Robert
authors.initials: R
authors.lastname: Goldsby
authors.forename: Steven G
authors.initials: SG
authors.lastname: DuBois
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000671:Amputation, Surgical; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D012516:Osteosarcoma / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D011878:Radiotherapy; D018426:SEER Program; D016019:Survival Analysis; D013684:Telangiectasis; D016896:Treatment Outcome; D034941:Upper Extremity; D055815:Young Adult