A method of detecting the presence of glioblastomas and/or recurrent glioblastomas in a subject in need thereof includes isolating CD14+ cells from a blood sample of the subject and determining the ratio of isolated CD14+ cells expressing low levels of HLA-DR to isolated CD14+ cells expressing VNN2, wherein the subject has increased risk of glioblastomas or recurrent glioblastoma if the ratio of isolated CD14+ cells expressing low levels of HLA-DR to isolated CD14+ cells expressing VNN2 is greater than about 2.