Abstract
Objective:The aim of this study is to investigate the clinical role of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in patients with carcinoma of unknown primary (CUP).Methods:One hundred twenty one patients with a diagnosis of CUP who underwent whole body 18F-FDG PET/CT imaging were included in this retrospective study. The final diagnoses were confirmed either histopathologically or by clinical follow-up.Results:The 18F-FDG-PET/CT successfully detected the primary tumor in 59 out of 121 (49%) patients. The most common primary tumor as detected by 18F-FDG PET/CT was lung cancer (n=31). In a patient, two primary tumors (colon and prostate) were detected on PET/CT imaging. Bone marrow biopsy revealed prostate cancer in this patient and the colon cancer was accepted as a synchronous second primary tumor. 18F-FDG PET/CT findings were false-positive in 11 patients. 18F-FDG PET/CT could not detect any primary lesion in 51 patients, whose conventional work-up detected a primary tumor in 11 and thus considered as false-negative. The sensitivity, specificity rate and accuracy of 18F-FDG PET/CT in detection of primary tumor were identified as 84%, 78% and 82%, respectively.Conclusion:Whole body 18F-FDG PET/CT is an effective method for detecting the primary tumor in patients with CUP. In addition to detecting the primary tumor, it can also help determine disease extent and contribute to patient management.
Highlights
Carcinoma of unknown primary (CUP) refers to the presence of metastatic disease for which the site of the primary lesion remains unidentified after conventional diagnostic procedures
Ninety five out of 121 patients were proved to have metastases histopathologically and 26 patients had highly suspicious metastases by conventional imaging [8 patients with multiple lung metastases detected by CT, 10 patients with multiple bone metastases detected by scintigraphy and/or magnetic resonance imaging (MRI), 5 patients with multiple liver metastases by MRI and/or US, and 3 patients with brain metastases detected by MRI]
The bone marrow biopsy revealed metastatic prostate carcinoma the colon carcinoma was accepted as a synchronous second primary tumor
Summary
Carcinoma of unknown primary (CUP) refers to the presence of metastatic disease for which the site of the primary lesion remains unidentified after conventional diagnostic procedures. CUP accounts for approximately 2.34.2% of cancer in both men and women [1,2]. The mean survival is between 3-11 months, and only 25% of patients survive over one year [3,4]. Several studies have shown that survival of patients in whom the primary tumor has been detected was higher than that of patients in whom the primary tumor has remained unknown [5,6]. Various radiologic methods and serum tumor markers can be used for primary tumor detection. The primary tumor could be detected in less than 20% of patients with CUP [1]. Spontaneous regression or immune-mediated destruction of primary tumor or the small size of a primary tumor may be an explanation, it is not yet fully understood why primary tumors remain undetected [2,7,8]
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