OUTLINE: This is a randomized, multicenter study. Patients are randomized to receive procarbazine alone or in combination with isotretinoin. Arm I: Patients receive oral procarbazine once daily on days 1-14 every 28 days. Oral isotretinoin is administered every 12 hours on days 15-28 every 28 days. Patient receive 6 courses of combined therapy, then continue with oral isotretinoin alone on days 15-28 of each 28 day course, until disease progression or unacceptable toxicity. Arm II: Patients receive procarbazine by mouth once daily on days 1-14 followed by 2 weeks of rest. Patients receive a total of 6 courses of treatment in the absence of disease progression and unacceptable toxicity. Patients are followed until death.