18F-FDG PET/CT in Patients with Cancer of Unknown Primary Site

Abstract

Objective: This retrospective study was undertaken to address the results of PET/CT with 18F-FDG to determine the primary tumor origin of carcinomas with unknown primary site. Methods: Between February 2006 and October 2007, twenty-four patients (10 men, 14 women; mean age 55.5 years) with pathologically proven metastatic cancer of unknown primary site were referred to our PET/CT center. For all patients, extensive imaging was unsuccessful in localizing the primary site. Each patient underwent a PET/CT scan carried out according to a standard procedure (6 h of fasting, intravenous injection of 370 MBq of 18F-FDG and whole body image acquisition with a dedicated PET/CT scanner). Results: Twenty-three patients were eligible for analysis except a woman (#16) who had underlying breast cancer. In 9 patients (39.1%), FDG PET/CT showed a primary tumor site which was confirmed by follow-up or surgery. In another 6 patients (26.1%), the primary tumor site was suggested by FDG PET/CT but not confirmed by clinical outcome. No primary tumor was found on PET/CT image in the other 8 patients (38.1%). Conclusion: In our study, FDG PET/CT allowed the identification of primary tumor site in about forty percent of patients with unknown primary tumor. The encouraging results, if validated by larger patient population, support the use of PET/CT in patients with carcinoma of unknown primary origin.