Value of FDG PET/CT in the assessment of chemotherapy response of germ cell cancer

Objectives The goal of this study is to evaluate the role of FDG PET/CT for monitoring chemotherapy response in patients with metastatic germ cell cancer.

Methods 16 pts age between 28 to 61y (42.1y±10.2y) who underwent chemotherapy for metastatic germ cell cancer (9 seminoma, 6 non-seminoma) and post-therapy FDG PET/CT scans were included. 14 had both pre and post-therapy scans, among them 5 also had interim scans (before the completion of therapy regiments). 2 pts did not have a pre-therapy scan and one of them had an interim scan. PET/CT was performed on a GE 64 slice scanner (Discovery STE) with average 15 mci of F-18 FDG . Correlation CT scans were performed with contrast (7 pts) or without contrast (9 pts). Pts with negative FDG PET/CT scans were followed clinically. Positive scans were compared with pathology.

Results All pre-therapy scans showed abnormal FDG uptake in metastatic lesions with SUVmax ranges from 1.6 to 17.5, average 8.8±5.7. Post-therapy scans in 13 pts had no abnormal FDG uptake (SUVmax below or equal to background activity). Among these 13 responders, 10 patients had residual adenopathy and only 2 pts had resolution of adenopathy on CT. One pt had only bone metastases which were not appreciated on CT. All 13 pts that had negative FDG uptake after therapy remained disease free during clinical follow up an average of 27.8 ±14.8 months (ranges 6 to 60 months). All six interim studies showed complete resolution of abnormal uptake and was confirmed by post-therapy scans. One seminoma and two non-seminoma patients had positive uptake ( SUVmax >2.8) after standard chemotherapy. All had confirmed active disease pathologically. Two pts died shortly after completion of initial therapy. One had recurrence even after resection of positive nodal disease. The sensitivity and specificity of predicting post-therapy response based on FDG activity were both 100%.

Conclusions Post-therapy and likely interim FDG PET/CT are very accurate in the assessment of chemotherapy response for metastatic germ cell cancer.