Benz, M. et al. FDG-PET/CT imaging predicts histopathologic treatment response after the initial cycle of neoadjuvant chemotherapy in high-grade soft-tissue sarcomas. Clin. Cancer Res. 15, 2856–2863 (2009).

Credit: Image supplied by F. Eilber, UCLA, US

Early assessment of treatment response is crucial in patients with soft-tissue sarcoma. A prospective study has examined whether changes in tumor 18F-fluorodeoxyglucose (FDG) uptake could predict histopathologic treatment response in patients with high-grade soft-tissue sarcoma after the initial cycle of neoadjuvant chemotherapy. Neoadjuvant chemotherapy is often ineffective and is associated with adverse effects; early prediction of response is, therefore, necessary. As changes in tumor size cannot predict histopathologic response and patients' outcomes early during the course of therapy, the combination of FDG-PET with CT might be an important strategy in the management of patients with sarcoma.

In total, 50 patients with high-grade soft-tissue sarcoma undergoing neoadjuvant chemotherapy and tumor resection were prospectively enrolled in the study. Combined FDG-PET and CT was performed before treatment (baseline), after the first cycle (early follow-up) and after completion (late follow-up) of neoadjuvant chemotherapy. The researchers assessed treatment response by histopathologic examination of the resected tumor specimen, and patients with ≥95% pathologic necrosis were classified as responders.

FDG uptake decreased significantly in responders (16%) when compared with nonresponders (84%) at early follow-up. At least a 35% reduction in FDG uptake between baseline and early follow-up was observed in all responders and 33% of nonresponders. Sensitivity and specificity for the prediction of histopathologic response were 100% and 67%, respectively, when a reduction of ≥35% in FDG uptake was used as the early metabolic response threshold. CT did not predict response.

“A 35% reduction in tumor FDG uptake at early follow-up is a sensitive predictor of histopathologic tumor response. Early treatment decisions, such as discontinuation of chemotherapy in nonresponding patients, could be based on FDG-PET criteria,” conclude the researchers.