FDG PET imaging guided re-evaluation of histopathologic response in a patient with high-grade sarcoma.

[(18)F]fluorodeoxyglucose positron emission tomography (FDG PET) is used to evaluate the metabolic activity of intermediate- to high-grade soft tissue sarcomas prior to the initiation of chemotherapy. FDG PET and MRI are repeated after chemotherapy to assess treatment response and to correlate this with the histologic response. This case report highlights discrepant results between the final histologic diagnosis (tumor response) and the percent change in maximum standard uptake variable (SUV(max)). Further investigation of the resected specimen identified the significant difference in tumor response assessment to be due to the heterogeneity of the tumor and heterogeneity in its response to treatment. FDG PET imaging has an important role in evaluating tumor metabolic activity and has played an increasingly important part in evaluating the response to neoadjuvant chemotherapy in sarcomas. Evaluating the heterogeneity of the tumor at baseline and after response to therapy can provide insight into prognosis and treatment planning.