Inclusion Criteria:

- Age 2 to < 18 years

- Ewing's sarcoma, soft tissue sarcoma, neuroblastoma, brain tumors or other malignancy
(excluding any form of leukemia) requiring treatment with high dose chemotherapy and
autologous transplant as rescue therapy

- Eligible for autologous transplantation

- Recovered from all acute significant toxic effects of prior chemotherapy

- Adequate performance status (for patients ≥16 years of age, defined as Karnofsky
score >60 and for patients <16 years of age, defined as Lansky score >60)

- Absolute neutrophil count >1.0 × 10^9/L

- Platelet count >75 × 10^9/L

- Calculated creatinine clearance (using the Schwartz method): during study Stage 1,
>80 mL/min/1.73m^2 and during study Stage 2, >60 mL/min/1.73m^2

- Aspartate aminotransferase(AST)/serum glutamic oxaloacetic transaminase(SGOT),
alanine aminotransferase(ALT)/serum glutamic pyruvic transaminase (SGPT) and total
bilirubin <3 × upper limit of normal

- The patient and/or their parent/legal guardian is willing and able to provide signed
informed consent

- Patients who are sexually active must be willing to abstain from sexual intercourse
or agree to use an approved form of contraception while receiving plerixafor and/or
standard mobilization treatment and for at least 3 months following any plerixafor
treatment

Exclusion Criteria:

- Any form of leukemia

- A co-morbid condition which, in the view of the Investigator, renders the patient at
high-risk from treatment complications

- Previous stem cell transplantation

- Patients with tumors frequently involving bone marrow (e.g., lymphomas and
neuroblastoma) will be expected to have had evaluation of their marrow as part of
their standard staging evaluations. Persistent high percentage marrow involvement
prior to mobilization will be prohibited.

- A residual acute medical condition resulting from prior chemotherapy

- Acute infection

- Fever (temperature >38.5°C) - if fever is between 37°C and 38.5°C, infection must be
excluded as a cause

- Pulse oximetry ≤92%

- Known human immunodeficiency virus (HIV) positive

- Positive pregnancy test in post pubertal girls

- History of clinically significant cardiac abnormality or arrhythmia

- Use of an investigational drug which is not approved in any indication either in
adults or pediatrics within 4 weeks prior to the first dose of G-CSF to be
administered as part of the patient's planned standard mobilization regimen, and/or
during the study up until engraftment of the transplant. Drugs approved for other
indications that are being used in a manner considered standard of care for this
transplant procedure are allowed

- The patient (and/or their parent/legal guardian), in the opinion of the Investigator,
is unable to adhere to the requirements of the study