CHI3L1 and neoplasm: CHI3L1 and osteopontin levels in the patient CSF and serum are potential biomarkers for CNS diseases such as CNS lymphoma,42 histiocytosis43 and multiple sclerosis.44–46 In the case of traumatic brain injuries, resident cells in the CNS, likely the macrophages, secrete osteopontin to control the inflammation and repair the tissues, as demonstrated in models of ischemic stroke.47,48 Thus, we believe coherent that, by producing similar cytokines, DIPG maintains the immunoprivileged state of the CNS and create a favorable environment for tumor growth.