Role of 18F-FDG PET-CT imaging for the detection of an unknown primary tumour:: preliminary results in 21 patients

Purpose: Metastatic cancer of unknown primary origin is a syndrome characterised by a poor prognosis, with a typical survival rate from diagnosis of no longer than 1 year. Only 20 - 27% of primary tumours are identified by conventional radiological imaging. By contrast, it has been reported that F-18-fluorodeoxyglucose positron emission tomography (FDGPET) allows the identification of 24 - 40% of otherwise unrecognised primary tumours. To our knowledge, the studies on this topic have been conducted using F-18-FDG PET imaging alone. The aim of this study was to evaluate the potential additional diagnostic role of fused F-18-FDG PET-CT imaging for the detection of metastatic occult primary tumours. Methods: The study population consisted of 21 consecutive patients with biopsy-proven metastatic disease and negative conventional diagnostic procedures. Each patient underwent a PET scan, carried out according to a standard procedure ( 6 h of fasting, i.v. injection of 370 MBq of F-18-FDG and image acquisition with a dedicated PET-CT scanner for 4 min per bed position). Results: F-18-FDG PET-CT detected the occult primary tumour in 12 patients (57% of cases), providing a detection rate higher than that reported with any other imaging modality, including conventional F-18-FDG PET. Conclusion: The favourable results of this study need to be confirmed in larger patient populations with long-term follow-up.