In addition, vitamin D metabolism is directly regulated by calcidiol 1-monooxygenase (CYP27B1) and vitamin D 1,25-hydroxylase (CYP105A1) downstream of the metabolic subpathway 00100_6, and studies have shown that the level of 25-hydroxyvitamin D (25(OH)D) in the serum of intermediates of vitamin D metabolism is opposite to that of patients with GBM-specific subtypes (59). Here, CYP27B1 is linked to glioblastoma.