Metabolic Differences Between Esophageal Adeno- and Squamous Cell Carcinomas Measured with 18F-MISO and 18F-FDG PET

657 Objectives: Esophageal cancer still remains a malignancy with poor prognosis. A variety of treatment modalities are available, dictated by the stage of the disease. It is still on debate whether therapy should also consider the histological type of the tumors. The latter would make sense if metabolic differences between the tumor entities become visible. The study compares glucose metabolism and hypoxia of adenocarcinomas (AC) and squamous cell carcinomas (SCC) measured with positron emission tomography (PET) in vivo. Methods: 20 Patients with histologically proven esophageal carcinoma (9 SCC, 11 AC) underwent two PET examinations on a whole body scanner using standard protocols (ECAT EXACT 922, 2D-Acquisition, attenuation correction, iterative reconstruction). FDG-uptake was assessed by definition of regions of interest and calculation of “standard uptake values” after static acquisition (SUVmax and SUVmean). Dynamic 18F-MISO scans were acquired consisting of 32 frames with total scan duration of 180 min. SUVmax and SUVmean were calculated using summarized last three frames. Hypoxic fraction was defined as ratio volume_FMISO / volume_FDG. PET results were correlated to the percentage of viable tumor cells in histopathology after radio-chemotherapy and tumor resection (% Tu_cells). Results: The hypoxic fraction represented a noticeable part of the tumor volume (AC 14.6%; SCC 23.1%). The FMISO accumulation was significantly higher in AC than in SCC (AC SUV_FMISOmax=2.4±0.4 and SUV_FMISOmean=2.1±0.4; SSC SUV_FMISOmax=1.9±0.4 and SUV_FMISOmean=1.6±0.4; t-test p Conclusions: Differences in the tumor metabolism of esophageal AC and SCC support therapy concepts considering histology in addition to tumor stage. The correlation between FDG and FMISO accumulation and the percentage of viable tumor cells in histopathology after tumor resection could be useful in response evaluation.