SUVmax on ¹⁸F-FDG PET/CT and Histopathological Necrosis in Osteosarcoma and Ewing Sarcoma

This study is aimed at evaluating the relationship between preoperative ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) findings and histopathological necrosis rates following chemotherapy in patients diagnosed with osteosarcoma (OST) and Ewing sarcoma (EWS).

Patients diagnosed with OST and EWS between 2017 and 2023 were retrospectively analyzed. Data recorded included preoperative ¹⁸F-FDG PET/CT findings, demographic characteristics, histopathological diagnosis, maximum standardized uptake value at diagnosis (SUVmax1), maximum standardized uptake value after neoadjuvant chemotherapy (SUVmax2), the SUVmax change ratio (SUVmax2/SUVmax1 = SCR), and the percentage of tumor necrosis in resected specimens.

A total of 49 patients (33 OST and 16 EWS) were included, consisting of 22 females (44.9%) and 27 males (55.1%) with a median age of 12 years (range: 4-20). Median SUVmax1, SUVmax2, and SCR values were 6.8 (0-22.5), 2.5 (0-9.42), and 0.38 (0-1.44), respectively. The median tumor necrosis percentage was 20% (range: 0-100). Stratification according to SUVmax2 (< 2.5 vs. ≥ 2.5) revealed no significant difference in necrosis percentage (p = 0.234). No significant correlation was observed between SCR and necrosis percentage (p = 0.102). However, a significant inverse correlation was found between SUVmax2 and necrosis percentage in the overall cohort (p = 0.040, r = -0.295), which was more pronounced in OST patients (p = 0.014, r = -0.426).

¹⁸F-FDG PET/CT is a valuable imaging modality for predicting histopathological response in solid tumors. Consistent with adult studies, our findings demonstrate that post-NACT FDG uptake is inversely correlated with tumor necrosis percentage, particularly in pediatric OST patients. These results highlight the potential of ¹⁸F-FDG PET/CT as a noninvasive prognostic tool to assist in early identification of poor responders.