The impact of 18F-FDG PET/CT in the clinical management of patients with lymph node metastasis of unknown primary origin

The aim of this study was to evaluate the diagnostic performance and the utility of F-18-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) in the clinical management of patients presenting with lymph node metastasis of undefined primary origin (CUP). A total of 53 patients (34 males, 19 females) with a diagnosis of lymph node metastasis according to the histopathology and/or conventional imaging were enrolled in this retrospective study. Patients were divided into four groups according to the initial location of their metastasis - group 1, cervical lymph nodes (n=39), group 2, axillary lymph nodes (n=6), group 3, mediastinal lymph nodes (n=2) and group 4, abdominal and pelvic lymph nodes (n=6). The site of a probable primary malignancy suggested by PET/CT was confirmed by biopsy/further investigations or follow-up. 18F-FDG PET/CT accurately detected the primary carcinoma in 19 of 53 patients (36%), with head and neck cancer and lung carcinoma being the most common primary locations. The PET-CT scan results were negative for primary site localization in 13% of patients (false-negative), while 45% had true negative results, and 6% displayed false-positive results. Additional distant metastatic foci were identified in 21 of all patients (40%). The overall sensitivity, specificity, and accuracy rates of the study were identified as 73%, 89%, and 81%, respectively; in the group with cervical lymph node metastasis sensitivity 70% and specificity 84%. To conclude, 18F-FDG PET/CT is a sensitive and selective procedure for detecting unknown primary tumors, especially in the clinical setting of cervical lymph node metastasis and its use should be encouraged earlier in the pre-treatment phase of CUP-patients, leading to higher detection of probable primary sites, guiding subsequent biopsy, and more accurate detection of distant metastases in a single examination.