Immunotherapy with immune checkpoint inhibitors (ICIs) has revolutionized contemporary oncology, presenting efficacy in various solid tumors and lymphomas. However, ICIs may potentially overstimulate the immune system, leading to immune-related adverse events (irAEs). IrAEs may affect multiple organs, such as the colon, stomach, small intestine, kidneys, skin, lungs, joints, liver, lymph nodes, bone marrow, brain, heart, and endocrine glands (e.g., pancreas, thyroid, or adrenal glands), exhibiting autoimmune inflammation. ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) is commonly used in oncology for staging and assessment of therapy responses, but it may also serve as a tool for detecting irAEs. This review aims to present various patterns of metabolic activation associated with irAEs due to ICI treatment, identifiable through ¹⁸F-FDG PET/CT. It describes the advantages of early detection of irAEs, but also presents the challenges in differentiating them from tumor progression. It also delves into aspects of molecular response assessment within the context of pseudoprogression and hyperprogression, along with typical imaging findings related to these phenomena. Lastly, it summarizes the role of functional PET imaging in oncological immunotherapy, speculating on its future significance and limitations.

The aim of the study was to compare the results of single-photon emission computed tomography-computed tomography (SPECT-CT) with those of intraoperative gamma probe detection and assess the clinical utility of SPECT-CT for sentinel lymph node biopsy in endometrial cancer. We investigated 70 patients with endometrial cancer who underwent total abdominal hysterectomy, bilateral salpingo-oophorectomy, and sentinel lymph node biopsy (routine pelvic and para-aortic lymphadenectomy was additionally performed in high-risk patients). Tc-99m radiocolloid albumin was injected into the cervix and a blue dye was injected superficially into the fundus. SPECT-CT revealed hot spots in 64 patients (91.4%). The detection rates were 97.1 and 94.3% using the combined technique and the hand-held gamma probe, respectively. In 19 cases (27.1%) 35 hot spots detected on SPECT-CT were not diagnosed as sentinel lymph nodes (SLNs) during surgery. In each patient with undetected hot spots located in the common iliac or para-aortic regions, hot SLNs were found during surgery in the obturator or external iliac region. In addition, SPECT-CT had detected 88.9% of the SLNs found during surgery. With respect to the 13 cases not detected on SPECT-CT, the hot SLNs had very low activity. Using the combined method, 95.1% of SLNs were found in typical locations (external iliac or obturator nodes). There were two metastatic nodes: one in SLN and one in nonsentinel node. SPECT-CT yields a high SLN detection rate; however, there is significant discrepancy in comparison with intraoperative findings, which limits its clinical utility. In addition, in the majority of cases SLNs are found in typical areas, which means that they can be reliably detected using an intraoperative gamma probe.