Role of FDG PET/CT in Patients With Metastasis of Unknown Origin

Cancer of unknown primary origin (CUP) includes a cluster of heterogeneous tumors that have exceptional clinical features: it is defined as early apparent metastatic disease with no recognizable primary site at the time of presentation. The incidence of CUP ranges around 2% of all new cancer diagnoses.

The work up list of CUP include; a biopsy proven malignancy, a detailed physical examination, many laboratory, radiological and endoscopy. However, these investigations may be costly time-consuming and may eventually fail to detect the site of the primary malignant tumor in the majority of patients. In this context, positron-emission tomography (PET) combined with computed tomography (PET/CT), using the radiotracer 18F fluoro- 2-deoxyglucose (FDG) is an alternative, non-invasive imaging modality with accurate diagnostic performance. It considered good tool for diagnosis of patients with CUP . The basis for use of FDG as radiotracer for PET imaging in CUP depends on the fact that most of the malignant cancer phenotypes show an increased glucose metabolism rate.

Failure to identify the primary tumor hampers optimization of management planning, which in turn may adversely influence patient prognosis.