DISEASE CHARACTERISTICS:

• Histologically confirmed* neurofibromatosis type 1 (NF1)-associated plexiform neurofibromas (PN) that are inoperable AND have the potential to cause significant morbidity including, but not limited to, any of the following:

  • Head and neck lesions that could compromise the airway or great vessels
  • Brachial or lumbar plexus lesions that could cause nerve compression and loss of function
  • Lesions that could result in major deformity (e.g., orbital lesions) or significant cosmetic problems
  • Lesions of the extremity that could cause limb hypertrophy or loss of function
  • Painful lesions NOTE: *Histologic confirmation of tumor is not required in the presence of consistent clinical and radiographic findings, but is required if any clinical observation or scan suggests possible malignant transformation.

• Patients with PN that has not been histologically confirmed must have ≥ 1 other diagnostic criteria for NF1 (according to NIH Consensus Conference criteria), including any of the following:

  • Six or more café-au-lait spots (> 0.5 cm in prepubertal patients or > 1.5 cm in postpubertal patients)
  • Freckling in the axilla or groin
  • Optic glioma
  • Two or more Lisch nodules
  • Distinctive bony lesion (dysplasia of the sphenoid bone or dysplasia or thinning of long bone cortex)
  • First-degree relative with NF1

• Meets 1 of the following criteria:

  • Progressive PN (with or without clinical symptoms), as defined by 1 of the following (stratum 3):

    • Presence of new PN on MRI within the past 12 months
    • Measurable increase of the PN (≥ 20% increase in volume, ≥ 13% increase in the product of the two longest perpendicular diameters, or ≥ 6% increase in the longest diameter) on the last two consecutive MRI or CT scans or over a time period of approximately 1 year prior to study entry
  • PN with no clinical symptoms and no documented radiographic progression (stratum 1)
  • PN with clinical symptoms but no documented radiographic progression (stratum 2)
• Complete tumor resection is not feasible OR patient refuses surgery

• Measurable residual tumor

  • Measurable lesion is defined as a lesion that measures ≥ 3 cm in one dimension
• No evidence of an optic glioma requiring treatment with chemotherapy or radiotherapy
• No history of malignant peripheral nerve sheath tumor

PATIENT CHARACTERISTICS:

• Karnofsky or Lansky performance status 50-100%
• Life expectancy ≥ 12 months
• Absolute granulocyte count > 1,500/μL
• Hemoglobin > 10 g/dL
• Platelet count > 100,000/μL
• Bilirubin < 1.5 mg/dL
• SGPT ≤ 2 times upper limit of normal

• Creatinine clearance ≥ 70 mL/min OR serum creatinine normal based on age as follows:

  • 0.8 mg/dL (for patients 5 years of age and under)
  • 1.0 mg/dL (for patients 6-10 years of age)
  • 1.2 mg/dL (for patients 11-15 years of age)
  • 1.5 mg/dL (for patients over 15 years of age)
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• Able to return for follow-up visits or obtain follow-up studies required to assess toxicity and response to therapy
• No clinically significant unrelated systemic illness (i.e., serious infections or significant cardiac, pulmonary, hepatic, or other organ dysfunction) that, in the judgment of the Principal or Associate Investigator, would compromise the patient's ability to tolerate PEG-interferon alfa-2b or that would likely interfere with the study procedures or results
• No other cancer except surgically cured nonmelanoma skin cancer or carcinoma in situ of the cervix

• No severe cardiovascular disease, including any of the following:

  • Arrhythmias requiring chronic treatment
  • Congestive heart failure
  • Symptomatic ischemic heart disease
• No pre-existing severe psychiatric condition or history of a psychiatric disorder requiring hospitalization
• No history of suicidal ideation or attempt
• No thyroid dysfunction not responsive to therapy
• No uncontrolled diabetes mellitus
• No history of seropositivity for HIV
• No medical condition requiring chronic systemic corticosteroids
• No known active alcohol or drug abuse

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• Recovered from all prior therapy
• No prior interferon alfa-2b or PEG-interferon alfa-2b
• More than 30 days since prior investigational agents
• At least 21 days since prior surgery
• No other concurrent immunotherapy, biologic therapy, chemotherapy, hormonal therapy, or radiotherapy
• No other concurrent investigational drugs
• No concurrent colony-stimulating factors, including epoetin alfa and filgrastim (G-CSF)
• No concurrent chronic systemic corticosteroid therapy