PSMA-Positive Low Malignant Gastrointestinal Stromal Tumor in the Stomach on F-18-PSMA-1007 PET/CT

Abstract

A 76-year-old man with newly diagnosed high-risk prostate cancer was referred for primary staging with F-18-PSMA-1007 PET/CT. The PET/CT scan showed no lymph node or bone metastases, only localized disease within the prostate gland. Additionally, the F-18-PSMA PET/CT scan showed a PSMA-positive lesion correlating to a polyp located in the body of the stomach on the greater curvature. A prior F-18-FDG PET/CT showed low FDG uptake in the polyp, but this was not reported initially in the written report. The patient had no upper gastrointestinal symptoms. A gastroscopy with biopsies was performed, and the histopathology results showed chronic unspecific inflammation with no granulomas, dysplastic or malignant changes in three out of three biopsies. A repeated gastroscopy with biopsy showed an epithelioid variant of a gastrointestinal stromal tumor (Ki-67 index 2%). A laparoscopic tumor extirpation was planned after radiation treatment in combination with endocrine therapy of the localized prostate cancer. To our knowledge, this is one of very few reported cases of a PSMA-positive gastrointestinal stromal tumor (GIST), and can be added to the list of malignant pitfalls of PSMA PET/CT in prostate cancer patients.