Palliative therapy as a single agent or in established combination therapy w/ other approved chemotherapeutic agents in: Brain tumors- glioblastoma, brainstem glioma, medulloblastoma, astrocytoma, ependymoma, metastatic brain tumors; multiple myeloma in combination w/ prednisone; Hodgkin's disease as secondary therapy in combination w/ other approved drugs in patients who relapse while being treated w/ primary therapy, or who fail to respond to primary therapy; non-Hodgkin's lymphomas as secondary therapy in combination w/ other approved drugs for patients who relapse while being treated w/ primary therapy, or who fail to respond to primary therapy.