Serum or plasma compounds such as VEGF, glial fibrillary acidic protein, plasma free amino acid profiles, and CSF concentrations of uric acid, D-dimers, and MMP-2 and MMP-9 have been quantified in dogs with brain tumors, but results to date suggest that these compounds will not fulfill ideal biomarker criteria due to limitations associated with sensitivity and specificity (59–65). The gene discussed is MMP9; the disease is brain neoplasm.