Positron emission computed tomography with 18F-fluorodeoxyglucose in the diagnosis and management of patients with cancer from an undetected primary focus (literature review with own observations)

Cancer metastases from cancer of unknown primary (CUP) is a widespread heterogeneous group of diseases characterized by malignant metastases from an undetected primary source, which could not be detected even after a thorough diagnostic search. CUP is on the 6th - 8th place in the world in terms of prevalence among malignant neoplasms. It accounts for 2.3 to 6 % of new cancer diagnoses. It also occupies the 3rd - 4th place in the structure of mortality from cancer. According 89 to recent studies, the prognosis of survival of patients with CUP is unfavorable, on average less than one year. Based on the biological features, the clinical picture and the picture of metastasis, CUP can be considered as a separate disease, different from other oncological diseases with known primary tumor localization, the frequency of which can be reduced by early detection of the primary tumor site due to improved diagnostic capabilities that have appeared with the use of PET-CT and its combination with other diagnostic methods. This review examines the pathogenesis, prevalence, survival prognosis, risk factors, molecular biology and classification of CUP. The algorithms of diagnostic search for metastases from CUP, visualization methods used in the diagnosis of this disease are analyzed. The possibilities and prospects of using PET-CT with 18F-FDG in the diagnosis of CUP in comparison and combination with other diagnostic methods, which open up probable prospects in the field of the approach to the treatment of patients with CUP, are investigated and evaluated.