IDH2 and neoplasm: Although GFAP expression is commonly elevated in tumor tissue, its detection in serum is limited due to intratumoral heterogeneity and the so-called "sensitivity gap." Nonetheless, serum GFAP levels correlate with tumor burden, necrosis, and IDH status, and GFAP remains a valuable marker for circulating tumor cell identification (Jelski and Mroczko, 2021).