The value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in carcinoma of an unknown primary: diagnosis and follow-up.

Background: The management of the patients with carcinoma of an unknown primary represents a difficult challenge in oncology. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) has provided new insights in the diagnosis, staging, and follow-up of oncological patients.

Aim: This study aimed to investigate the value of FDG PET/CT in clarifying the primary site in our patients with histologically proven tumor metastasis (HPM) or with a high clinical suspicion of malignancy, and the clinical impact of this technique on the management of these patients.

Methods: In total 94 patients from two centers underwent FDG PET/CT imaging; 78 patients with HPM and 16 patients with a clinical suspicion of malignancy. The histology and/or follow-up data were used as the gold standard. Hypermetabolic findings at the site of the pathological CT changes or at physiological FDG uptake sites were the criteria for malignancy. PET/CT findings were analyzed for the identification of the primary tumor site, for the relationship with survival, and also for the effect in chemotherapy monitoring.

Results: Primary malignancy was discovered in 53 of 90 patients (59%) histologically and 37 (41%) patients' primary tumor sites were not found during the study period. Amongst 90 patients, five (6%) were normal on FDG PET/CT. Of 85 patients (94%) with pathological findings on FDG PET/CT, 27 patients (32%) had solitary and 58 (68%) patients had multiple organs affected. Regarding the whole study population, a sensitivity of 74% and a specificity of 78% were calculated for FDG PET/CT imaging. Regarding the patients with HPM, the sensitivity and specificity values were 84 and 81%, respectively. The mean survival time of the patients with disseminated disease was significantly shorter than those of the patients with single or no lesion (13.44+/-1.61, 20.98+/-2.0 and 26.67+/-2.73 months, respectively, P=0.014). In seven of eight patients, follow-up FDG PET/CT scans effectively monitored the patients' therapies.

Conclusion: Whole-body FDG PET/CT has to be considered a useful method, especially in an early phase of the diagnostic workup of patients with carcinoma of an unknown primary syndrome, to optimize the management.