The purpose of this study is to find out what effect an antibody called Humanized 3F8 (Hu3F8) and a drug called GM-CSF have on the patient and whether it can keep the patient in remission longer and/or prevent recurrence of the disease.

Inclusion Criteria:

• Patients must have recurrent OS. OS must be verified by histopathology review by the site's Department of Pathology. (Patients registered at MSK must have pathology confirmed by MSK Department of Pathology.)
• Patients must be in a ≥2nd complete remission as indicated by appropriate radiologic evaluations at the time of study entry.
• Patients must be ≥ 1 year of age and ≤ to 40 years of age at the time of enrollment.
• Prior therapy: ≥3 weeks should have elapsed since last cytotoxic therapy, immunotherapy or radiation therapy. More than one week should have elapsed since major surgery.

NOTE: Minor surgery (e.g. minor biopsy, central venous catheter placement, shunt revision) is permitted within 1 week prior to enrollment)

• Adequate hematopoietic function defined as:

  • Absolute neutrophil count ≥ 500/ul
  • Absolute lymphocyte count ≥ 500/ul
  • Platelet count ≥ 50,000/ul (transfusion independent)

• Adequate hepatic function as defined by:

  • Total bilirubin of ≤ 1.5 times upper limit of normal (exception is made for patients with Gilbert's syndrome who may be considered eligible if total bilirubin is ≤ 3 times upper limit of normal).
  • AST (SGOT) of ≤ 3 times upper limit of normal
  • ALT (SGPT) of ≤ 3 times upper limit of normal

• Adequate renal function as defined by a serum creatinine of ≤ 1.5 times upper limit of normal

• Adequate cardiac function as defined by a shortening fraction of ≥ 28% or an ejection fraction ≥ 50%

• Adequate pulmonary function as defined by no evidence of dyspnea at rest at no history of exercise intolerance

• Adequate performance status as defined by ECOG score of ≤ 2 or Karnofsky/Lansky score ≥ 50%

• Prior treatment with other anti-GD2 antibodies is allowed (prior treatment with Hu3F8 is NOT allowed), but HAHA antibody titer must be negative

• Women of child-bearing potential must be willing to practice an effective method of birth control while on treatment

• Signed informed consent indicating awareness of the investigational nature of this program

Exclusion Criteria:

• Patients with OS in first complete remission.
• Presence of overt metastatic disease at any site.
• Active life-threatening infection.
• Pregnant women or women who are breast-feeding.
• Inability to comply with protocol requirements.