Medulloblastoma and gliomatosis cerebri: rare brain tumors in multiple sclerosis patients.

The simultaneous appearance of both multiple sclerosis (MS) and central nervous system (CNS) tumors is relatively uncommon. Whether the co-existence of two diseases is due to chance alone or the result of a causal relationship is still a matter of debate. There is also controversy about the effect of long-term exposure of MS patients to immunomodulatory drugs on the incidence of cancer.