Review of F-18 FDG PET/CT in Evaluating Response to Immunotherapy Treatment

Abstract

AbstractIntroduction: Immunotherapy is a wide-spreading therapeutic resource in oncology. The therapy is guided to improve the patient’s immune response to cancer cells, on the basis of the concept of immune surveillance by activating both cell-mediated and humoral immunity to fight cancer. Immunomodulatory monoclonal antibody therapy utilizes preformed monoclonal antibodies directed against molecular targets to regulate T-cell activation. There are three mechanisms involved in this kind of therapy: antibodies directed against the programmed death protein 1 (PD-1)/programmed death receptor ligand 1 (PD-L1), such as nivolumab and CTLA-4 inhibitors that prevent inhibition of the activated T-cells.Material and Method: Different reveiw articles were reviewed to understand the differences in response assessment of immunotherapy as compared to conventional chemotherapy or radiotherapy when using F-18 FDG PET/CT.Results: When using FDG PET/CT for response assessment, following important items should be considered: (1) Pseudoprogression: meaning that we can see transient enlargement of tumors or the appearance of new tumors followed by tumor shrinkage or long-term stability of tumor size. (2) Hyperprogression which is characterized by rapid increase in tumor burden (more than 50% increase compared to basal) and also time to treatment failure less than 2 months and more than 2 times increase in tumor growth rate, with deteriorating clinical condition. (3) Response to treatment is generally slower than with conventional cytotoxic chemotherapy. (4) Adverse effects (irAE) that are more easily diagnosed through FDG PET CT, than through conventional CT, and the importance of being able to recognize and report them sometimes life-threatening like pneumonitis or colitis. Also nuclear medicine physician should report inflammatory changes like drug induced sarcoid-like lymph nodes and differentiate from progression disease or splenic/liver SUV, moreover keeping in mind that there is evidence of good association between the presence of irAE and good answer to treatment. (5) Evolution of irAE comparing the actual PET with previous reporting the change in 18FDG uptake.Conclusion: Reporting of F-18 FDG PET/CT after immunotherapy, should consider these different items: Pseudoprogression, hyperprogression, irAE, evolution of irAE, and other inflammatory signs related to immunotherapy to improve our methodology efficiency.