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

Objective: To investigate the clinical value in detecting occult primary tumors with 18F-FDG PET-CT whole body imaging. Methods: 120 patients with unknown primary origin were referred for 18F-FDG PET-CT whole body imaging. All patients were performed 18F-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. Results: 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 18F-FDG PET-CT in the detection of the primary tumor site were 91.5%, 85.2%, and 88.3%, respectively. Conclusion: 18F-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 18F-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.