S-1 or Tegafur-Uracil in Treating Patients With Previously Treated Stage III or Stage IV Head and Neck Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed squamous cell carcinoma of the head and neck (SCCHN) * Stage III or IV disease * Primary tumor in the mesopharynx, hypopharynx, larynx (except T3 N0 tumors of the glottis), oral cavity, or maxillary sinus * Completed definitive treatment for SCCHN within the past 3 months, that included any of the following: * Surgery * Chemotherapy * Biologic therapy * Radiotherapy (e.g., radiotherapy in combination with chemotherapy or pre- or postoperative radiotherapy) * Any other treatment * No clinical evidence of locoregional tumors or distant metastasis within 3 months after the completion of definitive treatment PATIENT CHARACTERISTICS: * ECOG performance status 0-1 * WBC ≥ 3,500/mm\^3 AND ≤ 12,000/mm\^3 * Neutrophil count ≥ 2,000/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Hemoglobin ≥ 9 g/dL * AST and ALT \< 100 IU/L * Bilirubin \< 1.5 mg/dL * Creatinine \< 1.2 mg/dL * No uncontrolled cardiovascular disease * No interstitial pneumonia or pulmonary fibrosis * Must have sufficient oral intake PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No concurrent biologic therapy, radiotherapy, other chemotherapy, or any other therapy