High 18F-fluorothymidine uptake for invasive thymoma.

We report an invasive thymoma discovered incidentally by an 18F-FLT (fluorothymidine) PET study on a 48-year-old woman. The patient had equivocal breast lesions in her bilateral breasts. She entered a clinical 18F-FLT PET trial in our hospital to differentiate malignant breast tumors from benign ones. No 18F FLT-avid lesions in her breasts were revealed. But an intense 18F-FLT uptake lesion was noted in her right anterior mediastinum. However, an F-FDG PET scan showed only mild F-FDG uptake in the lesion. Video-assisted thoracic surgery thymectomy was subsequently performed, and the final pathology showed invasive thymoma.