Abstract
We assessed the role of [18F]FDG-PET/CT in identifying and managing cancer of unknown primary site (CUP syndrome). We reviewed [18F]FDG-PET/CT scans of individuals with CUP syndrome recorded in clinical referral letters from 2012 to 2019. We evaluated the identification of primary tumor (PT) by [18F]FDG-PET/CT, according to histological subtype, and the impact on clinical management. The median age was 65 years, 36/64 males (56%). PTs were detected in 28/64 (44%) patients. Detection was significantly lower in patients with squamous cell carcinoma (SCC) than with other histologies combined, p = 0.034. Mean age, mean SUVmax (10.6 ± 6.0) and organ involvement were similar between patients with and without discovered PTs; and between patients with SCC and with other histologies combined. However, those with SCC were less likely than the others to present with multi-lesion involvement, p < 0.001. [18F]FDG-PET/CT interpretations apparently affected treatment of 8/28 (29%) patients with PT detected, and in none of the 35 whose PT was not discovered, p < 0.001. [18F]FDG-PET/CT appeared helpful in detecting PT in almost half the patients with CUP syndrome; the lowest rate was for patients with SCC pathology. PET/CT showed limited overall value in guiding clinical management, however benefited those with discovered PT.
Highlights
Abbreviations CUP Cancer of unknown primary site primary tumor (PT) Primary tumor squamous cell carcinoma (SCC) Squamous cell carcinoma PET Positron emission tomography [18F]FDG 18-Fluorine-fluorodeoxyglucose SUVmax Maximum standardized uptake values maximum intensity projection (MIP) Maximum intensity projection MRI Magnetic resonance imaging CT Computed tomography US Ultrasound
In the current study of patients with CUP syndrome and negative conventional imaging, [18F]FDG-PET/CT detected the PT in only 1 (10%) of the patients with SCC compared to 50% of all those with other pathologies
The greater detection of PTs in pathologies other than SCC compared to SCC did not have clinical implications
Summary
Abbreviations CUP Cancer of unknown primary site PT Primary tumor SCC Squamous cell carcinoma PET Positron emission tomography [18F]FDG 18-Fluorine-fluorodeoxyglucose SUVmax Maximum standardized uptake values MIP Maximum intensity projection MRI Magnetic resonance imaging CT Computed tomography US Ultrasound. CT and conventional MRI enable the detection of only 22–36% of the primary sites of CUP syndrome[1,6] These low detection rates have been attributed to functional limitations of these imaging modalities. While the use of [18F]FDG-PET/CT in the detection of primary tumors (PTs) in CUP syndrome has been suggested for at least two d ecades[3,10,11], its roles in the diagnostic workup of patients with disseminated CUP syndrome remain inconclusive[12]. The primary purpose of this study was to assess the role of [18F]FDG-PET/CT in the identification of PTs, and in the management of CUP syndrome in patients with negative conventional diagnostic workup. The secondary objectives were to evaluate the ability of [18F]FDG-PET/CT in discovering PTs according to their histological subtypes, and to evaluate the impact on clinical management
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