Positron emission tomography (PET) is more sensitive and more accurate than computed tomography (CT) for assessment of response to treatment in patients with sarcomas, according to an article in the February 1 issue of Clinical Cancer Research.

The study was conducted by a multidisciplinary team at the University of California Los Angeles Jonsson Cancer Center. From January 2005 to January 2007, 42 patients with resectable biopsy-proven high-grade soft-tissue sarcoma underwent a FDG-PET/CT scan before and after neoadjuvant treatment. Relative changes in tumor glucose uptake and size from baseline to the follow-up scan were calculated; their accuracy for assessment of histopathologic response was compared by receiver operating characteristic curve analysis. Histopathologic response was defined as at least 95 percent tumor necrosis.

Researchers found that standard, size-based evaluation (computed tomography) only identified 20 percent of responders, while PET was able to identify all responders.

Current practice evaluates response to treatment using RECIST, or Response Evaluation Criteria in Solid Tumors. Patients are scanned using CT or MRI before and after treatment and the scans are compared to determine if the tumor has decreased in size.

"We knew from our considerable experience with neoadjuvant therapy in sarcoma patients that measuring tumor size correlated poorly with response," said Fritz Eilber, MD, an assistant professor of surgery, director of the Sarcoma Program at UCLA's Jonsson Cancer Center, and senior author of the study. "We have removed many tumors that have not changed in size with treatment or have even grown, but are completely dead on pathologic analysis. Just because the tumor doesn't shrink doesn't mean the treatment didn't work."

The combined PET/CT scanner allowed researchers to directly compare before and after treatment scans for both tumor size and metabolic activity.

"PET was much more sensitive in picking up response than size-based RECIST," Eilber said. "RECIST missed a large percentage of patients that actually had a response. PET picked up all of the responders."

"Evaluating biologic responses to therapy is the future of cancer imaging," Eilber concluded.