[18F] FDOPA standardized uptake values of brain tumors are not exclusively dependent on LAT1 expression.

[18F]-FDOPA is a labeled amino acid (AA) analog used for positron emission tomography (PET) which is gaining increasing interest in the evaluation of brain tumors (BT). The AA-transporter LAT1 has been shown to be involved in [18F]-FDOPA uptake. The aim of this study was to determine whether the [18F]-FDOPA uptake was correlated with level of LAT1 expression in BT. Twenty-eight BT (including 19 gliomas and 9 metastases) were investigated by [18F]-FDOPA-PET prior to surgery and by anti-LAT1 immunohistochemistry on surgical specimens. The quantitative [18F]-FDOPA measured parameters were SUVmax, SUVmean and SUVpeak. LAT1 expression was quantified using a score (0 to 400). A significant [18F]-FDOPA uptake was associated with a LAT1 score ≥ 100 (p = 0.02) but there was no linear correlation between intensity of [18F]-FDOPA uptake and score of LAT1 expression whatever the parameters considered. LAT1 expression alone is not sufficient to explain variation of intensity of [18F]-FDOPA uptake in BT.

[Is FDG TEP CT practice changing in the management of sarcomas in adults?]. / Évaluation de l'utilisation de la TEP au FDG pour le bilan des sarcomes de l'adulte en pratique quotidienne.

BACKGROUND: FDG PET (PET)±computed tomography (CT) has increasingly been used in some areas of oncology imaging. It is sometimes performed outside recommendations, at diagnosis or monitoring of sarcomas. We assessed the value of PET-CT in routine practice in sarcomas. MATERIAL AND METHODS: All consecutive sarcoma adult patient charts presented at the multidisciplinary sarcoma meeting in a tertiary care center over a period of 10months were examined in order to analyze the performances of PET-CT when available. RESULTS: Of 232 patients, 50 (21 %) underwent a PET-CT. Sensitivity and specificity of PET-CT were 94.7 %, 57.1 %, respectively. SUV values were highly variable, including for a given histology or grade. PET-CT resulted in practice changing in 14 % of cases. When extrapulmonary metastases are suspected and for some subtypes of sarcomas, PET-CT could provide additional information because in view of its good sensitivity. CONCLUSION: Given the most frequent pulmonary tropism, first hand chest CT may be sufficient at first diagnostic work-up for the detection of pulmonary metastases. However, the relatively poor specificity suggests that further analyses should be performed to identify clinical situations where PET-CT may be of added value compared to current standards.

Study of LAT1 Expression in Brain Metastases: Towards a Better Understanding of the Results of Positron Emission Tomography Using Amino Acid Tracers.

Positron emission tomography using radiolabeled amino acid (PET-AA) appears to be promising in distinguishing between recurrent tumour and radionecrosis in the follow-up of brain metastasis (BM). The amino acid transporter LAT1 and its cofactor CD98, which are involved in AA uptake, have never been investigated in BM. The aim of our study was to determine and compare the expression of LAT1 and CD98 in BM and in non-tumoral brain tissue (NT). The expression of LAT1 and CD98 were studied by immunohistochemistry in 67 BM, including 18 BM recurrences after radiotherapy, in 53 NT, and in 13 cases of patients with previously irradiated brain tumor and investigated by [18F] FDOPA-PET. LAT1 and CD98 expression were detected in 98.5% and 59.7% of BM respectively and were significantly associated with BM tissue as compared to NT (p<0.001). LAT1 expression in recurrent BM was significantly increased as compared to newly occurring BM. Ten cases investigated by [18F] FDOPA-PET corresponding to recurrent BM displayed significant [18F] FDOPA uptake and LAT1 overexpression whereas three cases corresponding to radionecrosis showed no or low uptake and LAT1 expression. LAT1 expression level and [18F] FDOPA uptake were significantly correlated. In conclusion, we hypothesized that BM may overexpress the AA transporter LAT1. We have shown that LAT1 overexpression was common in BM and was specific for BM as compared to healthy brain. These results could explain the specific BM uptake on PET-AA.