The invention relates to the use of the monoclonal antibody NILO1 for the diagnosis, treatment and/or prevention of brain tumors and lesions. Particularly, the invention relates to methods for the diagnosis of brain tumors and brain lesions in which cells marked with said antibody, or with immunologically active fragments thereof, are detected. The invention also relates to the use of said monoclonal antibody, or immunologically active fragments thereof, as a medicament for the treatment and/or prevention of brain tumors and brain lesions. In a preferred embodiment of the invention, the monoclonal antibody NILO1, or its immunologically active fragments, are humanized.