MAINTENANCE THERAPY: Patients receive cisplatin IV over 6 hours on day 1, vincristine sulfate IV over 1 minute on days 1 and 8, and cyclophosphamide IV over 1 hour on days 2 and 3. Patients also receive filgrastim subcutaneously (SC) or IV beginning on day 4 and continuing until blood counts recover (at least 10 days). Treatment repeats every 28 days for a total of 6 courses in the absence of disease progression or unacceptable toxicity.