Non-invasive blood biomarkers provide accessible and cost-effective alternatives for MS subtype classification, disability monitoring, and disease prognosis.11 Even as biomarkers like neurofilament light chain (NfL)12 and glial fibrillary acidic protein (GFAP)13 enter clinical practice, there are rooms for improvement throughout the clinical contexts of MS care. Here, GFAP is linked to myeloid sarcoma.