Phenylbutyrate and Valganciclovir in Treating Patients With Relapsed or Refractory Epstein-Barr Virus-Positive Cancer

DISEASE CHARACTERISTICS: * Biopsy-proven Epstein-Barr virus (EBV)-positive malignancy * Must have tissue analysis to confirm EBV positivity * Archival tissue ≤ 1 year old may be used * Any of the following malignancies: * WHO type II or III nasopharyngeal carcinoma * Post-transplant lymphoproliferative disorder * Nasal NK/T-cell lymphoma * Hodgkin's lymphoma * Lymphoepithelioma-variant gastric carcinoma * AIDS-related lymphomas * Patients with CNS non-Hodgkin's lymphoma must have tumor cells present in the cerebrospinal fluid (and assessable with lumbar puncture) * Relapsed or refractory disease * Must have received and failed all prior potentially curative treatment for disease * Eligible only for salvage therapy * Must have tumor tissue amenable for minimally invasive biopsy (e.g., fine-needle aspiration or bone marrow biopsy) * No brain tumors not amenable to biopsy * CNS metastases allowed provided ≥ 2 weeks since prior radiotherapy PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Life expectancy ≥ 3 months * Absolute granulocyte count ≥ 500/mm³ * Platelet count ≥ 50,000/mm³ * Bilirubin ≤ 1.5 times upper limit of normal * Creatinine ≤ 2.0 mg/dL OR creatinine clearance ≥ 40 mL/min * Recovered from uncontrolled intercurrent illness, including, but not limited to, any of the following: * Ongoing or active infection * Symptomatic congestive heart failure * Unstable angina pectoris * Cardiac arrhythmia * Able to take medica…