Objective: To investigate the role of 18fluoro-2-deoxyglucose positron emission tomography (FDG-PET) in the initial staging of clinical stage I and II nonseminomatous germ cell tumours (NSGCTs) and in re-staging (non)seminomatous GCTs after chemotherapy.
Patients and methods: FDG-PET studies were undertaken in 50 patients. FDG uptake was interpreted visually and when possible the standardized uptake value was determined. A FDG-PET scan was taken in five patients with clinical stage I and in seven with stage II NSGCT. The scans were validated by histology. Stage I patients underwent a retroperitoneal lymph node dissection because of vascular invasion in the primary tumour. Thirty-eight scans were taken after completing chemotherapy (28 NSGCTs and 10 seminomatous GCTs), and validated by histology or clinical follow-up.
Results: In stage I NSGCT, FDG-PET staging was equivalent to computed tomography (CT) staging. One small lesion, consisting of mature teratoma, was missed by both FDG-PET and CT. In stage II NSGCT, FDG-PET missed two lesions (mature teratoma and retroperitoneal mass with a small component of embryonal cell carcinoma) whereas CT correctly classified all. In 20 of 28 patients with NSGCT, histology was obtained after chemotherapy. In one of three patients with viable tumorous residual mass the FDG-PET scan was clearly positive; in four of 12 with mature teratoma and inflammation components retroperitoneally, the FDG-PET was also positive. In contrast, eight patients with solitary mature teratoma had a negative PET result. In four of five patients with necrosis after chemotherapy the PET result was correctly negative. All eight patients on surveillance had a negative PET scan and were free of disease at median (range) of 14 (8-18) months. Interestingly, of the 12 patients with a correct negative PET result, 11 had no mature teratoma in their primary tumour. Nine of 10 patients with SGCT were correctly staged. Two FDG-PET studies showed increased uptake; in one, a viable seminomatous mass was found and in the other there was inflammation in the residual mass. In all other patients the FDG-PET scan correctly predicted absence of viability in the residual mass.
Conclusions: In primary staging, FDG-PET has no benefit over CT. In re-staging, a negative FDG-PET result predicts fibrotic residual mass in seminomatous GCT. Moreover, it could be useful to predict fibrotic residual mass in NSGCT in those patients with no teratoma component in their primary tumour.