In line with the above findings, we aimed to explore the role of the TGFB1-509C/T SNP in the genetic predisposition to brain tumors and its association with circulating levels and tissue expression of TGF-β1 and the clinical parameters of patients from the Bulgarian population who were operated on high-grade primary glial tumors or brain metastases. The gene discussed is TGFB1; the disease is glioma.