Detection of primary tumors and lymph node staging using FDG PET in gastric cancer; a comparison study with CT

This study was performed to compare FDG PET with CT in evaluation of primary tumors and lymph node metastases of gastric cancer. Eighty-one patients(28F: 53M, a mean age of 56.6 yrs, age range: 32-82 yrs) who had undergone radical (n=74) or palliative (n=7) gastrectomy and lymph node dissection for management of gastric cancer were included in this study. Preoperative FDG PET and computed tomography (CT) were performed in all patients within 2 weeks of each other. For primary tumors of the stomach, any focally increased FDG uptake more than the adjacent normal gastric wall was considered positive for malignancy. Lymph node staging was classified into 3 groups based on anatomical sites of regional lymph nodes. Lymph nodes were considered positive or negative based on the group as a whole single unit. For detection of primary tumors of the stomach, both PET and CT showed a sensitivity of 47% (8/17) for EGC and 98% (63/64) for AGC. The sensitivity of CT for N1 disease was higher than that of PET with a statistical significance. FDG PET had a sensitivity, specificity, and accuracy of 32.3%(10/31), 94%(47/50), and 70.4%(57/81) for N2 metastases, respectively. In comparison, the values for CT are 41.9%(13/31), 84%(42/50), and 67.9%(55/81), respectively. For N3 lymph node metastases, both PET and CT had the same sensitivity, and accuracy of 42.9%(3/7), 98.6%(73/74), and 93.8%(76/81). Overall, the sensitivity, specificity, and accuracy of FDG PET were not significantly different from those of CT for N2 or N3 lymph node metastases. FDG PET is as accurate as CT in the detection of primary tumors of the stomach. CT is more sensitive than PET for N1 disease. PET appears to be more specific than CT whereas CT seems to be more sensitive than PET in staging N2 disease. The high positive predictive value of FDG PET for N2 disease may have an important role in determining the extent of surgery avoiding limited lymph node dissection for advanced disease