Role of FDG PET/CT for detection of primary tumor in patients with extracervical metastases from carcinoma of unknown primary

Abstract

AimTo explore the diagnostic performance of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) to detect the primary tumor site in patients with extracervical metastases from carcinoma of unknown primary (CUP). We evaluated patient outcomes as overall survival (OS). Materials and methodsIn a single-center, retrospective study (2005–2019), patients with extracervical metastases from CUP underwent FDG PET/CT to detect primary tumor sites. The final diagnosis was based on histopathology/or clinical follow-up of at least 12 months. ResultsA total of 83 patients [Male 41 (49%), mean age 59 ± 14 years, range: 32–83 years] fulfilled the inclusion/exclusion criteria and were enrolled for analysis. The primary tumor was detected in 36 out of 83 (43%) patients based on histopathology/or clinical follow-up. PET/CT suggested the primary tumor site in 39 (47%) patients with diagnostic accuracy of 87%, sensitivity 89%, specificity 85%, PPV 82%, NPV 91% and detection rate 39%. Patients with oligometastases (<3) (2.16 years, 1.04–2.54) and primary unidentified (1 year, 0.34–2.14) had longer median survival time compared to the patients with multiple metastases (0.67 years, 0.17–1.58, p = 0.009) and primary identified (0.67 years,0.16–1.33, p = 0.002). The SUVmax of the primary or metastatic lesions with maximum uptake was not significantly related to survival. ConclusionsPET/CT could reveal the primary tumor site in 39% of the patients. It demonstrated the metastatic disease burden and distribution in patients with ‘primary obscured’, which directs management. Patients with multiple metastases and primary identified had a poorer prognosis. In patients with primary unidentified after PET/CT, a further search was futile.