[The role of whole body 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography in the management of unknown primary tumors].

OBJECTIVE: To assess the role of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) in the management of unknown primary primary (CUP) with metastatic loci.

METHODS: Thirty-four patients of CUP with metastatic loci who had undergone unsuccessful conventional diagnostic work-up underwent (18)F-FDG PET/CT. The images thus obtained were analyzed with visual and semi-quantitative methods. Histopathology, cytology, and/or follow-up were used to evaluate the PET/CT results.

RESULTS: In 20 of the 34 patients (18)F-FDG PET/CT showed focal tracer accumulations corresponding to potential primary tumor sites located in the lung (n = 9), colon (n = 3), rectum (n = 2), pancreas (n = 1), right aryepiglottic wall (n = 1), esophagus (n = 1), breast (n = 1), and ovary (n = 2). The detection rate of primary tumor by (18)F-FDG PET/CT was 50.0% (17/34), the primary tumors were identified in the lung (n = 8), colon (n = 2), rectum (n = 1), pancreas (n = 1), right aryepiglottic wall (n = 1), esophagus (n = 1), ovary (n = 2), and breast (n = 1). The false positive rate was 8.8% (3/34) with the diagnosis of primary tumor in the lung (n = 1), colon (n = 1), and rectum (n = 1) to be identified as false. In 14 of the 34 patients, (18)F-FDG PET/CT did not reveal lesions suspected to be the primary tumor sites in 13 patients, and it was impossible to identify one lesion as the most likely primary tumor in one patient due to the presence of multiple hot spots in several organs. The (18)F-FDG PET/CT findings affected the medical management in 17 of the 34 (50.0%) patients due to the finding of primary sites and/or additional metastases.

CONCLUSION: (18)F-FDG PET/CT has relevant impact on the therapeutic management of patients with unknown primary tumor. It is recommended that (18)F-FDG PET/CT be performed in the patient with unknown primary tumor after unsuccessful conventional diagnostic workup.