18F-FAMT-PET Is Useful for Judging Clinical Complete Response in Advanced Esophageal Cancer Patients Who Have Received Definitive Chemoradiotherapy

We developed l-[3-18F]-α-methyltyrosine (18F-FAMT) as an amino acid tracer for positron emission tomography (PET) imaging. In esophageal cancer, the specificity of 18F-FAMT PET was significantly higher than that of fluoro-2-deoxy-d-glucose (18F-FDG) PET and computed tomography (CT) in the evaluation of individual lymph node groups. Definitive chemoradiotherapy (CRT) has been considered a potentially curative treatment for locoregional esophageal cancer and may achieve the same survival benefits as surgical resection. Clinical evaluation of complete response (CR) is important using several modalities. We evaluated 6 patients who had been diagnosed with clinical CR by FAMT-PET following definitive CRT for esophageal squamous cell carcinoma between June 2008 and July 2012. Treatment evaluation of 18F-FAMT was performed following CRT and approximately 1 month later. In primary tumors, 66.7% of patients (4/6) showed FDG uptake following CRT, whereas that of FAMT was 33.3% (2/6). In lymph node metastases, 50% of patients (3/6) showed FDG uptake following CRT, whereas that of FAMT was 0% (0/6). In the present study, FAMT-PET following CRT was a useful modality to predict clinical CR in esophageal cancer. There is a limit to judging clinical CR by CT or FDG-PET following CRT, because radiation-related esophagitis and reactive mediastinal lymphadenopathy by FDG and wall thickness by CT still remain 1 month following CRT. FAMT-PET is the most useful modality at the present time.