Melanin-targeted [18F]-PFPN PET imaging may shed light for clear cell sarcoma

Purpose Intracytoplasmic melanin pigment is a characteristic of clear cell sarcoma (CCS), which is a particularly deadly type of soft-tissue sarcoma. [F-18]-N-(2-(diethylamino)ethyl)-5-(2-(2-(2-fluoroethoxy)ethoxy)ethoxy)picolinamide ([F-18]-PFPN) is a positron emission tomography (PET) probe characterized by high melanin affinity. Therefore, this study aimed to investigate the feasibility of melanin-targeted [F-18]-PFPN PET in patients with CCS.Methods This prospective single-centre study recruited patients with pathologically confirmed CCS. [F-18]-FDG PET/computed tomography and [F-18]-PFPN PET/magnetic resonance imaging scans were performed within 1 week of each other. The lesion numbers and [F-18]-FDG and [F-18]-PFPN PET parameters (maximum standardized uptake value [SUVmax], mean standardized uptake value [SUVmean], metabolic/melanotic tumour volume [MTV/MLTV], and total lesion glycolysis/melanin [TLG/TLM]) were collected.Results Three patients with CCS were recruited and received PET imaging. A total of 56 lesions were detected on [F-18]-PFPN PET, including primary tumour and distant metastases. Identical lesions were not detected on [F-18]-PFPN and [F-18]-FDG PET. Twelve lesions (12/39, 30.77%) on [F-18]-FDG imaging were missed on [F-18]-PFPN, and 20 lesions (20/47, 42.55%) on [F-18]-PFPN imaging were missed on [F-18]-FDG. In quantitative analysis, the [F-18]-FDG SUVmean (4.60 +/- 3.24) was higher than the [F-18]-PFPN SUVmean (3.0 +/- 2.63) in all lesions (P=0.01). No significant correlations were found between the SUVmax, SUVmean, MLTV/MTV, and TLM/TLG values of [F-18]-PFPN and [F-18]-FDG (P>0.05).Conclusion Melanin-targeted [F-18]-PFPN PET imaging is feasible for the diagnosis of CCS. Different imaging features were displayed on [F-18]-PFPN and [F-18]-FDG PET imaging, demonstrating the complementary role of the tracers. Combined use of the two imaging modalities would be preferred in patients with CCS.