The unexpected finding of a hemangioblastoma on the cerebellum of a patient undergoing treatment with natalizumab for multiple sclerosis

Natalizumab, a humanized recombinant monoclonal antibody used for the treatment of multiple sclerosis (MS), affects the flow of lymphocytes into the central nervous system (CNS). The drug binds to the alpha-4 chain of the alpha-4-beta-1 integrin (very late activation antigen 4 or VLA-4) and alpha-4-beta-7 integrin. Natalizumab decreases the numbers of CD4+ and CD8+ T lymphocytes, CD19+ B cells and CD138+ plasma cells in the cerebrospinal fluid of patients with MS receiving this therapy.1 Thus, at least in theory, this mechanism of action could compromise the immune surveillance within the CNS2 and favor the growth of tumors. There have been reports on primary central nervous system lymphoma in patients undergoing treatment with natalizumab,3-5 but the association between these two findings has been deemed unlikely by some.