Correlation between 18F-FDG PET-derived parameters and quantitative pathological characteristics of soft tissue sarcoma

Background: F-18-fluorodeoxyglucose (F-18-FDG) positron emission tomography (PET) has been widely used for evaluating patients with soft tissue sarcoma (STS). However, uncertainties and overlap among individuals may be observed, and the relevance of these findings remains to be further explored. The present study was aimed at investigating the correlation between PET metabolic parameters and quantitative pathological characteristics in STS.Methods: We retrospectively collected 39 patients with STS who underwent 18F-FDG PET/computed tomography (CT) examination before treatment. Metabolic parameters including the maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and intratumoral FDG uptake heterogeneity (IFH) were measured. Histological grading was performed according to the French Federation of Cancer Centers grading system. Continuous staining of tissue sections and digital quantitative analysis methods were used, the characteristics of tumor nucleated cells were observed through hematoxylin-eosin staining, and the expression of CD163, CD68, CD8, and CD4 in tumor tissues was determined by immunohistochemistry (IHC), then the correlation between FDG metabolic parameters and the above quantitative pathological characteristics in patients with STS were evaluated.Results: The SUVmax of F-18-FDG PET/CT in STS was positively correlated with the total nuclear area (r=0.355, P=0.027). SUVmax was also positively correlated with the expression levels of CD163, CD68, CD8, and CD4 (r=0.582, 0.485, 0.343, and 0.324, with P<0.001, 0.002, 0.032, and 0.044, respectively), but was not significantly correlated with cell count and mean nuclear area (all P>0.05). However, MTV, TLG, and IFH were not significantly correlated with the above quantitative pathological characteristics. Further multivariate logistic regression analysis indicated that only CD163 expression and histological grade were independently correlated with SUVmax. Moreover, SUVmax remained positively correlated with CD163 expression in the low-grade STS (r=0.820, P=0.001) and high-grade STS groups (r=0.430, P=0.028).Conclusions: F-18-FDG uptake was positively correlated with the quantitative pathological features of soft tissue tumors. SUVmax may be a meaningful method reflecting the level of M2 macrophage infiltration and may provide additional valuable information for preclinical evaluation of STS.