Diagnostic performance of 18F-FDG PET/CT for the detection of occult primary tumors in squamous cell carcinoma of unknown primary in the head and neck: a single-center retrospective study.

Objective To investigate the diagnostic performance of 18F-FDG PET/computed tomography (CT) for the detection of occult primary tumors in patients with squamous cell carcinoma of unknown primary (SCCUP) in the head and neck. Patients From March 2016 to January 2020, 37 patients diagnosed as SCCUP before PET/CT were retrospectively reviewed. The diagnosis of SCCUP was made when an overt primary tumor location could not be found for histologically proven squamous cell cervical lymphadenopathy after a complete diagnostic workup which includes full medical history, physical examinations, flexible rhinolaryngoscopy and CT or MRI. The PET/CT images were visually assessed by two nuclear medicine radiologists. Histopathological investigations after the PET scan served as the reference standard. Results The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of PET/CT for SCCUP were 71.4, 43.8, 62.5, 53.9 and 59.5%, respectively. PET/CT allowed identification of previously undetected lesions in 40.5% of the SCCUP patients. A total of 24 PET/CT scans indicated a positive result. Among them, nine were categorized into false-positive because of negative results from subsequent targeted and random biopsies. There were 13 PET/CT scans with a negative result, six of which, however, were revealed to have a primary site by subsequent random biopsies. Conclusion 18F-FDG PET/CT was shown to be useful in detecting a primary tumor for SCCUP, but had limitations in terms of both false-positive cases and false-negative cases. Therefore, histopathological investigations such as targeted and random biopsy should be viewed as necessary practice irrespective of PET/CT results.