Clinical application of 18F-FDG PET/CT in
 oncology: Rare gastrointestinal malignant tumors
 (literature review)

Abstract

Relevance: PET/CT is now becoming an integral part of cancer management protocols. 18F-fluorodeoxyglucose (18F-FDG)
 is the most common radiopharmaceutical for PET. However, the 18F-FDG PET/CT sensitivity and specificity vary widely in tumors of different histological structures and cell atypia degrees.
 The role of PET/CT in complex diagnostics of lymphomas is known. However, the specific use of this method in gastrointestinal neoplasms, especially at the initial stage of examination and in differential diagnostics, is not clearly defined since
 lymphomas account for only 1-5% of GI tumors.
 Neuroendocrine tumors (NETs) are a heterogeneous group of tumors that arise from the diffuse neuroendocrine system
 enterochromaffin cells. NETs account for 0.5% of all neoplasms but become more common recently due to the advances in diagnostics. However, the significant achievements in the study of biological and molecular mechanisms of NETs’ behavior have
 not yet resulted in a common algorithm for their diagnostics and treatment.
 The purpose of this study was to review the experience of using 18F-FDG PET/CT in diagnostics of lymphomas and gastrointestinal neuroendocrine tumors as rare tumors to improve the criteria for the rational use of the 18F-FDG PET/CT method in
 their diagnostics and monitoring.
 Results: The use of 18F-FDG PET/CT is advisable at any stage of non-Hodgkin lymphomas, which are most common in the
 gastrointestinal tract, and for differential diagnostics, primary staging, and treatment efficiency monitoring in gastrointestinal
 lymphomas. 18F-FDG PET CT is also most valuable in aggressive non-Hodgkin lymphomas.
 Despite the importance of functional imaging in NETs, 18F-FDG PET/CT plays a supporting role in monitoring gastrointestinal NETs. 18F-FDG PET/CT is known to be efficient in prognosing the outcome of radionuclide therapy with peptide receptors
 in low-grade and progressive metastatic NETs.
 Conclusion: In lymphomas, 18F-FDG PET/CT is useful for primary staging, assessing early response to treatment, and
 re-staging. 18F-FDG PET/CT has a diagnostic value in undifferentiated gastrointestinal NETs, while its usefulness in well-differentiated gastrointestinal NETs is limited.