The absolute counts of GFAP+CD16+ monocytes in the blood, also showed an increase in glioma and brain metastasis patients, but these absolute counts are relatively low and quit variable (median 31 cells/μl, range 0.6–1439 cells/μl), most likely because these counts are affected by confounding factors such as, immune cell kinetics, sample processing and medication. Here, GFAP is linked to central nervous system cancer.