FDG PET for Sarcoma
Dear OncoLink "Ask The Experts,"
Peeyush Bhargava, MD, Chief Fellow in the Department of Nuclear Medicine at the University of Pennsylvania, responds:
Although Medicare does not reimburse for PET imaging in patients with sarcoma, it has been proven to be a useful modality in several studies. It can be successfully used for differentiating benign from malignant tumors, especially in the setting of patients already treated for sarcoma, where the conventional anatomic imaging modalities (CT and MRI) cannot differentiate between residual disease and scar tissue.
PET with FDG gives metabolic information about the tissue, in the form of glucose utilization. The degree of FDG uptake in the tumor correlates well with the grade of tumor and patient survival (higher the SUV, higher is the tumor grade and poorer is patient survival). FDG PET is a great tool for detecting otherwise unsuspected metastasis, guiding biopsy to the most active part of the tumor and monitoring response to therapy.
Below are the images of a 56-year-old male with history of sarcoma of the small bowel. An FDG PET scan (image 3) was performed to rule out any recurrent disease (a year after the patients primary tumor was resected). It showed a focus of intense activity in the right lower quadrant of the abdomen (red arrow) consistent with recurrent disease. The CT scan done on the same day was negative and so was the repeat CT, 6 months later. An year after PET, the CT showed an ovoid mass in the right adnexa, suspicious for tumor recurrence. This was confirmed on MRI (image 1 and 2), which described the mass in the posterior right pelvis, with signal characteristics worrisome for tumor recurrence. This case illustrates the fact that metabolic changes (visualized early by FDG PET) occur much before anatomical changes (picked up later by CT and MRI) and their recognition can lead earlier diagnosis of recurrent cancer.