Prospective exploratory pilot study of 18 F-FMISO PET/CT for assessing tumor hypoxia in soft tissue sarcomas

Hypoxia is associated with poor outcomes in soft tissue sarcoma (STS) and is linked to increased expression of hypoxia-inducible factor 1-alpha (HIF-1α), carbonic anhydrase IX (CAIX), and lysyl hydroxylase 2 (PLOD2). These factors are potential therapeutic targets. This exploratory study aimed to investigate the correlation between 18F-fluoromisonidazole (18F-FMISO) positron emission tomography (PET) imaging, a marker of hypoxia, and the expression of these biomarkers in STS. This imaging phase II clinical trial (NCT #03730077) recruited 5 patients with suspected soft tissue sarcoma (STS) and imaged these patients with 18F-Fluorodeoxyglucose (18F-FDG) and 18F-FMISO within 2 weeks of each other. STS tissue was analyzed for HIF-1α, CAIX, and PLOD2 expression using immunohistochemistry and western blotting. Collagen formation was assessed by Masson’s trichrome. In this small sample, a correlation was found between STS size and PLOD2 expression (r = 0.996, P = 0.004). STS grade correlated positively with 18F-FMISO T/M (tumor/muscle) SUVmax (r = 0.894, P = 0.041). 18F-FDG correlated positively with 18F-FMISO SUVmax (r = 0.994, P = 0.006). Positive but non-significant associations were noted between 18F-FMISO T/M SUVmax and CAIX (r = 0.95, P > 0.05) and PLOD2 (r = 0.93, P > 0.05). These preliminary observations in a small sample are hypothesis-generating at best and must be interpreted with substantial caution due to the extremely limited number of patients, which precludes robust statistical inference and generalizability. No definitive conclusions can be drawn regarding the relationship between 18F-FMISO uptake and hypoxia biomarker expression. Larger, adequately powered prospective studies are essential to validate these findings, clarify potential correlations, and determine the clinical utility of 18F-FMISO PET/CT as a noninvasive hypoxia biomarker in STS. This small exploratory pilot study (n=5) of patients with soft tissue sarcoma found preliminary positive associations between 18F-FMISO PET/CT uptake and tumor grade, 18F-FDG uptake, and hypoxia-related biomarkers (particularly PLOD2 and CAIX), but these findings—limited by the very small sample size and lack of statistical significance for key correlations—remain hypothesis-generating and require validation in larger prospective studies. • Tumor size and PLOD2: In this small cohort (n = 5), larger soft tissue sarcomas showed higher PLOD2 expression (r = 0.996, P = 0.004) however confirmation is needed in larger studies. • Tumor grade and hypoxia: Higher-grade sarcomas were associated with increased hypoxia by 18F-FMISO T/M SUVmax (r = 0.894, P = 0.041) - a preliminary finding only. • Glycolysis and hypoxia link: 18F-FDG SUVmax strongly correlated with 18F-FMISO SUVmax (r = 0.994, P = 0.006); positive but non-significant trends seen with CAIX (r = 0.95) and PLOD2 (r = 0.93) (both P > 0.05), warranting further investigation in future studies.