This study is a prospective monocentric study aimed to evaluate the diagnosis and staging value of 18F-PFPN PET in clear cell sarcoma of soft tissue. Patients with clinically suspected or confirmed clear cell sarcoma of soft tissue will be recruited and 18F-PFPN PET/MR imaging will be performed. PET/CT imaging will be performed in patients with contraindications to MR. Additionally, to compare the diagnostic efficacy with the traditional imaging agent 18F-FDG, patients will also undergo 18F-FDG PET imaging, and the two imaging intervals will be completed two days apart. The general information, clinical data, 18F-PFPN and 18F-FDG PET/MR or PET/CT imaging results and other imaging data of the patients will be collected. The histopathology of the biopsy or surgical specimen, follow-up and other imaging examinations will be taken as evaluation references. This study plans to set the sample size as 10 cases.

Clear cell sarcoma of soft tissue is a rare malignancy derived from neural crest cells that contain melanin and/or melanin precursors. Melanin is an important target for the diagnosis of clear cell sarcoma of soft tissue. 18F-PFPN, a highly specific melanin-targeting positron probe, has been proven to have excellent pharmacokinetic properties and good biological safety, and can sensitively detect tiny melanin-containing lesions. Therefore, 18F-PFPN PET imaging is expected to be used in diagnosing and staging clear cell sarcoma of soft tissue.

This study was designed as a prospective study to explore the diagnosis and staging value of 18F-PFPN PET in clear cell sarcoma of soft tissue. In this study, patients with clinically suspected or confirmed clear cell sarcoma of soft tissue will be recruited to undergo 18F-PFPN PET/MR imaging. PET/CT imaging will be performed in patients with contraindications to MR. The general information, clinical data, imaging data and histopathology results of patients will be collected. The efficiency of diagnosis and staging of 18F-PFPN was evaluated by comparing the gold standard pathological diagnosis and the general metabolic imaging agent 18F-FDG.

Inclusion Criteria:

• Adult patients (age 18 years or above), regardless of gender;
• Patients with clinically suspected or confirmed clear cell sarcoma of soft tissue (supporting evidence including visual examination, MRI, CT, ultrasound, and histopathological examination, etc.) ;
• Patients who agree to undergo both 18F-PFPN and 18F-FDG PET imaging.

Exclusion Criteria:

• Acute systemic diseases and electrolyte disturbances;
• Patients who plan to get pregnant within six months or are pregnant or breastfeeding;
• The patient or his/her legal representative is unable or unwilling to sign the informed consent.