Ita-immuno-pet: the Role of Fdg Pet/ct for Assessing Response to Immunotherapy

Abstract

AIM: to examine the role of FDG PET/CT for assessing response to immunotherapy in patients with solid tumors. MATERIALS AND METHODS: data recorded in a multicenter (n=17), retrospective database between March and November 2021 were analyzed. The sample included patients with a confirmed diagnosis of a solid tumor who underwent serial FDG PET/CT (before and after one or more cycles of immunotherapy), who were >18 years of age, and had a follow-up of at least 12 months after their first PET/CT scan. Patients enrolled in clinical trials or without a confirmed diagnosis of cancer were excluded. The authors classified cases as having a complete or partial metabolic response to immunotherapy, or stable or progressive metabolic disease, based on a visual and semiquantitative analysis according to the EORTC criteria. Clinical response to immunotherapy was assessed at much the same time points as the serial PET images, and the two were compared. RESULTS: The study concerned 311 patients (median age: 67; range: 31-89 years) in all. The most common neoplasm was lung cancer (n=177, 56.9%), followed by malignant melanoma (n=101, 32.5%). Nivolumab was administered in 144 of the former patients (46.3%), and pembrolizumab in 126 of the latter (40.5%). Baseline PET and a first PET scan performed a median 3 months after starting immunotherapy were available for all 311 patients, while subsequent PET scans were obtained after a median 6, 12, 16, and 21 months for 199 (64%), 102 (33%), 46 (15%), and 23 (7%) patients, respectively. Clinical response to therapy was recorded at around the same time points after starting immunotherapy for 252 (81%), 173 (56%), 85 (27%), 40 (13%), and 22 (7%) patients, respectively. At successive time points, the consistency between PET scans and clinical findings was 37%, 54%, 26%, 37%, and 29%, respectively. After a median 18 (1-137) months, 113 (36.3%) patients had died. On Kaplan-Meier analysis, metabolic responders on two or more PET scans after starting immunotherapy had a better prognosis than non-responders (all p<0.001), while clinical response became prognostically informative from the second assessment after starting immunotherapy onwards. CONCLUSIONS: FDG PET/CT should have a role in the assessment of response to immunotherapy in patients with solid tumors. It can provide prognostic information and thus contribute to a patient’s appropriate treatment.