Positron emission tomography imaging of brain tumors.

Energy metabolism and amino acid transport and incorporation are important components of the pathophysiology of gliomas, about which molecular imaging is providing regional biologic information that is useful to clinical practice. Imaging hypoxia is straightforward and proliferation imaging with FLT shows significant promise. Neither has been exploited thoroughly enough to allow judgement of their potential benefit to the practice of neuro-oncology. Although cell division is the most distinguishing function of growth in tumors, probing membrane biosynthesis with PET and 1-[11C]acetate or a choline tracer may yield information as helpful as protein or DNA synthesis. Because astrocytic gliomas frequently carry epidermal growth factor receptor mutations at a frequency that is related to grade, a PET tracer that is specific for this mutated receptor could be useful for grading and prognosis [35]. Methods for imaging angiogenesis are being developed; 18F-labeling of a cyclic RGD-containing glycopeptide, cyclo(-Arg-Gly-Asp-D-Phe-Lys(sugar amino acid)-), with 4-nitro-phenyl 2-[18F]fluoropropionate has been reported [136]. 18F-labeled annexin V is being tested as a new PET agent for quantitating tumor cell death and predicting response to therapy. Annexin V binds to surface membranes that have exposed phosphatidyl serine residues resulting from programmed cell destruction. Recently, a Tc-99m-labeled derivative has been shown to accumulate in late stage lung cancer and lymphoma in response to chemotherapy [137]. As molecular pathways leading to and sustaining neoplasia become better understood, so will our capacity improve to measure them in vivo and intervene to the patient's advantage.