To investigate the biosignature of Nox4 expression and HIF-1 signal transduction within the tumor microenvironment, mice bearing 18-d orthotopic GBM8401/hif-1-r xenografts were injected intravenously with a perfusion marker (Hoechst 33342) and the tumors were removed for tissue immunofluorescence imaging. Here, NOX4 is linked to neoplasm.