Sokolova M.I., Pavlova V.I., Guz A.O. The role of FDG-PET/CT in the diagnosis of patientswith carcinoma of unknown primary. Head and neck. Russian Journal. 2025;13(1):55–62
DOI: https://doi.org/10.25792/HN.2025.13.1.55-62
Diagnosis of metastatic carcinoma of unknown primary (CUP syndrome) represents a clinical challenge, furthercomplicated by the rapid progression of the disease and low treatment sensitivity. The identification of the primarytumor plays a crucial role for diagnosis and treatment planning in such patients. Locating the primary lesion in patientswith CUP syndrome is one of the indications for fluorodeoxyglucose positron emission tomography combined withcomputed tomography (FDG-PET/CT).The purpose of the study was to assess the role of FDG-PET/CT in the identification of the primary tumor in patientswith CUP syndrome, to establish the rates of false-positive and false-negative results of the examination.
Material and methods. We carried out a retrospective analysis of data obtained from various sources: medicalrecords of outpatients and inpatients, discharge summaries, laboratory and instrumental examination reports,clinical recommendations for 84 patients with CUP syndrome treated at the Multidisciplinary Clinical MedicalCenter “Medical City” in Tyumen from 2016 to 2024. The PET-CT scanning was performed on Biograph mCT 20and Biograph 16 PET/CT scanners after intravenous administration of fluorodeoxyglucose (FDG) labeled with theultrashort isotope 18F.
Results. Males prevailed in the studied group of patients — 62 (74%) subjects. The dominant morphologic type of thedetected metastases was squamous cell carcinoma detected in 81% of cases. Most frequently (38%) metastaseswere localized at level II. In 14 (17%) cases, PET-CT detected primary tumor sites not previously identified by CTand magnetic resonance imaging. The most common occult localizations were the palatine tonsil (up to 7/50% ofcases), tongue root (2/14%), and nasopharynx (3/22). In a few cases, tumors were localized in the soft and hardpalate (1/7% each). The tumor was restaged in 6 (7%) patients after PET-CT imaging, while in the remaining patients,the stage was unchanged. In 2 patients, the management was changed after the FDG-PET/CT scanning. The false-positive rate was 5% with localization in the palatine tonsil, and false-negative rate reached 1% with localization inthe root of the tongue.
Conclusions. In addition to the role of FDG-PET/CT in cancer detection and disease staging in patients with CUPsyndrome, the method is also useful to assess the tumor extent, which is essential for treatment planning.
Keywords: CUP syndrome, fluorodeoxyglucose positron emission tomography combined with computed tomography
Conflicts of interest. The authors have no conflicts of interest to declare.
Funding. There was no funding for this study