PET outperforms CT in predicting sarcoma response to neoadjuvant therapy

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Quantitative PET with 18F-fluorodeoxyglucose (FDG-PET) was significantly more accurate than size-based criteria at assessing histopathologic response to neoadjuvant therapy in patients with high-grade soft-tissue sarcoma, according to a study published in the Feb. 1 issue of Clinical Cancer Research.

Vladimir Evilevitch of the Ahmanson biological imaging division at the University of California at Los Angeles (UCLA), and colleagues, said the aim of the study was to prospectively evaluate whether FDG-PET allows for a more accurate evaluation of histopathologic response.

The conventional approach to assessment of response has relied on change in tumor volume as determined by Response Evaluation Criteria in Solid Tumors (RECIST). However, multiple studies have shown RECIST as unreliable for predicting histopathologic response to therapy in soft tissue sarcomas, the authors wrote.

From January 2005 to January 2007, the researchers examined 42 patients with resectable biopsy-proven high-grade soft-tissue sarcoma, who underwent a FDG-PET/CT scan before and after neoadjuvant treatment. Histopathologic response was defined as ≥95 percent tumor necrosis.

The researchers found that in histopathologic responders (8 patients; 19 percent), reduction in tumor FDG uptake was significantly greater than in nonresponders, whereas no significant differences were found for tumor size. The area under the receiver operating characteristic curve for metabolic changes was 0.93, but only 0.60 for size changes.

Using a 60 percent decrease in tumor FDG uptake as a threshold resulted in a sensitivity of 100 percent and a specificity of 71 percent for assessment of histopathologic response, whereas RECIST showed a sensitivity of 25 percent and a specificity of 100 percent, the authors wrote.

On the basis of the findings, "evaluating biologic responses to therapy is the future of cancer imaging," according to Fritz C. Eilber, MD, co-author, from UCLA.