Mo1564 The Efficacy of 18F-FDG PET-CT and Wbbs in Detecting Bone Metastasis of Gastric Cancer: A Single-Center, Large-Volume Study in Korea

Abstract

Background/Aims: The role of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)-computed tomography (CT) and whole body bone scan (WBBS) in identifying bone metastasis in gastric cancer is not clear. We compared the usefulness of PET-CT and WBBS in detecting bone metastasis in patient with gastric cancer. Methods: 1,485 patients who were diagnosed as gastric cancer and taken PET-CT or WBBS were retrospectively reviewed from January 2003 to August 2011. 114 patients were enrolled and 73.2% of the patients were confirmed as bone metastasis. Positive indicators of bone metastasis were based on following criteria: presence of multiple asymmetric foci of increased radionuclide uptake over the skeleton on either PET-CT or WBBS without reasonable explanation other than metastasis; histologic examination; compatible findings on CT or MRI; and one or more equivocal lesions on PET-CT or WBBS with obvious progression on follow up examinations. Bone metastasis was confirmed when one or more criteria were met. Results: The mean duration from the diagnosis of gastric cancer to skeletal metastasis was 23.2 months. 78.6% of patients with skeletal metastasis had undifferentiated histology by Japanese classification and 69.0% had metachronous bone metastasis. Most of the patients (84.5%) had multiple bone metastasis and common sites were in order from the vertebra, pelvis, and ribs. The sensitivity, specificity, and accuracy of PET-CT were 88.1%, 10.0%, and 67.5% respectively. WBBS showed higher sensitivity, specificity, and accuracy than PET-CT such as 97.6%, 46.7%, and 84.2% respectively. When analyzed according to image modality, 85.7% of the patients with bone metastasis showed positive findings at both PET-CT and WBBS. Most of synchronous bone metastasis showed positive findings at both studies, however 15.5% of metachronous bone metastasis were positive at WBBS only. Based on the sites of bone metastasis, WBBS was more sensitive in detection of axial bones such as the vertebrae than PET-CT. Serologic markers such as alkaline phosphatase, CEA, and CA199 didn't show a significant difference between two studies. The concordance rate of response after treatment between PET-CT and WBBS was low (k=0.116). Conclusions: WBBS is more sensitive and specific than PET-CT for detecting bone metastasis in gastric cancer. Especially, WBBSmay bemore effective to detect metachronous bonemetastasis than PET-CT. For tumor assessment after treatment, both studies may be complementary due to low concordance rate between two studies.