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Cancer Epidemiol. 2012 Oct;36(5):470-5. doi: 10.1016/j.canep.2012.03.002. Epub 2012 Apr 14.

Clinical value of 18F-FDG PET-CT in detecting primary tumor for patients with carcinoma of unknown primary.

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  • 1Medical College of Shandong University, Department of Radiation Oncology, Shandong Cancer Hospital, 44# Wenhua Xi Road, Jinan 250012, Shandong, China.



To investigate the clinical value in detecting occult primary tumors with (18)F-FDG PET-CT whole body imaging.


120 patients with unknown primary origin were referred for (18)F-FDG PET-CT whole body imaging. All patients were performed (18)F-FDG PET-CT whole body scan. PET-CT images were interpreted by visual inspection and semi-quantitative analysis (standardized uptake value, SUV). Histopathological and formal clinical follow-up findings were used to assess the value of FDG PET-CT.


FDG PET-CT was able to detect the primary tumor in 54/120 patients (42.5%). The primary tumors were confirmed by histopathologic and formal clinical follow-up findings, and located in the head and neck (n=17), the lung (n=19), the breast (n=2), the esophagus (n=1), the stomach (n=2), the bile ducts (n=1), the pancreas (n=3), the co1on (n=3), the ovary (n=2), the prostate (n=l), others (n=3). FDG PET results were proved false positive in 9 patients (7.5%), which were located in the head and neck (n=3), the lung (n=1), the gastric (n=1), the colon (n=2), the ovary (n=1), the prostate (n=l). During the clinical follow-up of median 32 months (range, 2-45 months), primary tumor was found in only 5 patients of 60 cases unidentified by PET-CT (breast cancer, gastric cancer, co1on cancer, prostate cancer and urinary tumors, respectively). The sensitivity, specificity, and accuracy of (18)F-FDG PET-CT in the detection of the primary tumor site were 91.5%, 85.2%, and 88.3%, respectively.


(18)F-FDG PET-CT whole body imaging is both a noninvasive and a very sensitive tomographic whole-body imaging modality, allowing for the detection of a primary tumor and complete tumor staging in single examination, which can contribute substantially to selecting appropriate therapeutic methods and evaluating prognosis. Perhaps (18)F-FDG PET-CT whole body imaging should be used as a first-line imaging modality for patients with carcinoma of unknown primary rather than using it after other diagnostic procedures have failed to identify a primary tumor.

Copyright © 2012 Elsevier Ltd. All rights reserved.

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