We reported the utility of１８F-FDG-PET/CT examination for patients with cancer of unknownprimary origin. Twenty six patients（13 men, 13 women, aged 27-91 years, mean 71）were examined.The indication for PET/CT examination was tumor maker elevation（14 patients）, suspectedmetastatic tumor（14）and metastasis diagnosed histopathologically（3）. Patients weretold not to eat for at least four hours and a PET/CT image was obtained one hour after theadministration of 3.7MBq/kg FDG. From April to August 2006, 33 patients diagnosed with a cancerof unknown primary origin were referred to our hospital for PET/CT examination from anoutside institution. Twenty six patients could be investigated for outcomes. Seventeen patientsshowed an abnormal accumulation, with 14 of the 17 having their primary regions detected histopathologicallyor clinically. For one patient, the abnormal accumulation could not be determined toshow the origin. For 2 patients, it was difficult to diagnose if these abnormal accumulationsshowed the primary region or not, but CT examinations were helpful for a diagnosis. Seven of the9 patients who showed no abnormal accumulation were treated conservatively and the primaryregion for their cancer could not be detected during the follow up study. In 21 of 26 patients, theseresults were useful to select an appropriate therapy to be applied or a relevant examination. Weconsidered PET/CT examination, where it is possible to scan the whole body at one time, was veryuseful to get both morphologic and metabolic information. PET/CT examination showed a highersensitivity for detecting abnormal lesions than other imaging modalities
