Thymic squamous cell carcinoma mimicking lymphoma on 68Ga-FAPI PET/CT.

A 33-year-old man presented with progressive enlargement of supraclavicular fossa mass for 2 years. Recently, the patient feels neck pain when swallowing food. Previous chest CT imaging revealed an anterior mediastinal soft tissue mass without any evidence for adjacent vascular or lung invasion (approximately 4.1 cm × 3.4 cm in size), indicating a mediastinal tumor; therefore, malignancy could not be ruled out. With the consent of the patient, we enrolled him in a clinical trial of 68Ga-FAPI-04 PET/CT in tumors (ChiCTR2100044131). 68Ga-FAPI-04 PET/CT scan (▶ Fig. 1A-D) detected that the anterior mediastinal mass had intense FAPI uptake (SUVmax of 12.0). Based on these PET/CT findings, the lesion was suspected to be a mediastinal lymphoma. Subsequently, the patient underwent surgical resection of soft tissue mass. Immunohistochemistry revealed CK (+), CK19 (+), P63 (+), CD1a (+), TdT (+), CD5 (+), CD20 (+), CD117 (+), P53 (+, 50 %), Ki-67 (+, 40 %). However, the findings were consistent with thymic squamous cell carcinoma (SCC). Finally, the patient was well at the six-month follow-up visit.