Sensitivity of [18F]FDG PET/CT and classification of the primary tumor site in patients with carcinoma of unknown primary.

Background: The aim of this study is to find the sensitivity of the [18F]FDG PET/CT and the classification of the primary sites of carcinoma of unknown primary (CUP) as a single-center experience.

Material and methods: Sixty-eight patients with a mean age of 62.43 ± 12.78 years were included in this study retrospectively. Sixty-five patients had biopsy or surgery after PET/CT, which revealed pathological diagnoses of malign primary tumors, while primary tumor site could not be detected in three patients with histopathological examination. We evaluated the primary site of CUP with [18F]FDG PET/CT.

Results: Primary sites of three patients were not determined by histopathological examination. Malign lesions indicating the primary site of tumor were identified in 52 of 68 patients with PET/CT correctly. The primary tumor was lung cancer in 14 patients, cholangiocellular cancer in 9 patients, lymphoma in 9 patients, pancreas cancer in 6 patients, gastric cancer in 4 patients, ovary cancer in 4 patients, colon cancer in 4 patients, breast cancer in 3 patients, hepatocellular cancer in 2 patients, rectal cancer in 2 patients, sarcoma in 2 patients, esophagus, renal cell cancer, squamous cell cancer, endometrium cancer, malign melanoma, and multiple myeloma in 1 patient with histopathological examination. PET/CT was false positive in one patient. There were 13 patients in whom primary tumor could not be localized by PET/CT, but was diagnosed by histopathological evaluation.

Conclusions: PET/CT should be the first-line diagnostic tool for CUP, other diagnostic imaging tools should be applied after a negative whole-body PET/CT.