Lymphoid organs’ metabolism and its role in predicting the outcomes of patients with malignant melanoma treated with immunotherapy: an exploratory study

Background This study aimed to evaluate the changes in 2-[18F]-FDG PET/CT parameters of lymphoid organs and their association with clinical outcomes in melanoma patients undergoing immunotherapy. Materials and methods Ninety-two consecutive patients with malignant melanoma were enrolled in the study. Patients underwent serial 2-[18F]-FDG PET/CT scans at baseline (PET0), 6 months (PET1), 18 months (PET2), and 36 months after starting immunotherapy. Visual and semiquantitative analyses were performed by two experienced nuclear medicine specialists. Bone marrow uptake was visually quantified using a scale system ranging from 1 to 5, mean standardized uptake values (SUVmean) of the liver and spleen were measured, and the Spleen Liver Ratio (SLR) was calculated. Clinical assessments and disease outcomes were recorded based on physical examinations, routine blood work, serum chemistry studies, and conventional imaging. Progression-free survival (PFS) and overall survival (OS) were also determined. Results Most patients received anti-PD1 therapy, and radiotherapy was combined with systemic treatment in some cases (n = 12 patients). After 6, and 18 months, clinical disease control was achieved in 74% and 74%, respectively. Patients without clinical disease control exhibited higher bone marrow FDG uptake and an increase in the sites of metabolic lesions. Median SLR values were slightly higher in patients without disease control after 6 and 18 months, but lower after 36 months. At PET0, the median SLR was higher in alive patients than those who died, while it was similar in the following scans. Patients with signs of inflammation on PET1 had a higher baseline SLR, which decreased in the subsequent PET2 scan. Conclusions Changes in bone marrow FDG uptake may serve as potential indicators of treatment response and disease outcomes. SLR would be considered an interesting predictive and prognostic indicator. This study provides insights into the dynamic changes of metabolic parameters during immunotherapy and their clinical implications in malignant melanoma patients.