Prognostic significance of amino acid transport imaging in patients with brain tumors

OBJECTIVE: To evaluate the prognostic significance of presence, intensity, and extent of amino acid uptake in patients with suspected primary or recurrent brain tumors. METHODS: We retrospectively analyzed 181 consecutive studies of amino acid uptake using single-photon emission computed tomography and the amino acid L-[3-¹²³I]iodo-α-methyltyrosine (IMT). In a blinded analysis, all studies were evaluated for presence, maximal uptake (IMT_max), and extent (IMT_ext) of focal tracer uptake. RESULTS: The most frequent tumors were 53 astrocytomas (World Health Organization Grade I-III), 41 glioblastomas, 16 metastases, 13 oligodendrogliomas (Grade II-III), and 10 medulloblastomas. The other patients exhibited various parenchymal tumors or nonneoplastic lesions. IMT uptake was present in 69% of the patients with IMT_max ranging from 1.4 to 6.2. IMT_max and IMT_ext were significant predictors of survival in the whole group. When the group was divided according to primary versus recurrent tumor, only the primary tumors achieved a high level of significance (P < 0.01). When patients without any IMT uptake were excluded from the analysis, statistical significance for both IMT_max and IMT_ext was lost. Multiple regression analysis, including IMT_max, IMT_ext, age, and tumor grade, revealed only extent of IMT uptake as an independent predictor of prognosis. CONCLUSION: Absence of IMT uptake is a significant predictor of long-term survival in patients with suspected primary or recurrent brain tumors. Only the extent of a given lesion provided minor supplementary prognostic information as compared with histopathology and age. These findings suggest caution in relating high amino acid uptake values to poor prognosis, despite the capability of amino acid imaging to help determine the presence and extent of gliomas.