¹⁸ F-FDG uptake during early adjuvant chemotherapy predicts histologic response in pediatric and young adult patients with osteosarcoma

The purpose of this study was to determine the relationship of ¹⁸ F-FDG uptake in the primary tumor at diagnosis, during therapy, and after therapy with a histologic response and event-free survival in pediatric and young adult patients with osteosarcoma (OS). Methods: Serial (baseline and 5 and 10 wk after start of therapy) ¹⁸ F-FDG PET/CT imaging was performed in patients with newly diagnosed OS treated uniformly in a therapeutic trial at a single institution. Whole-body images were obtained approximately 1 h after injection of ¹⁸ F-FDG. Logistic regression was used to study the association of tumor uptake and changes in SUV _max between 0, 5, and 10 wk for both clinical endpoints. Results: Thirty-four patients (17 males; median age, 12.2 y; age range, 6.8–19.1 y) underwent PET imaging; 25 (74%) had localized disease. Primary tumor locations included the femur (n 5 17; 50%), tibia (n 5 9; 26%), and humerus (n 5 5; 15%). Logistic regression showed that SUV _max at 5 wk (P 5 0.034) and 10 wk (P 5 0.022) and percentage change from baseline at 10 wk (P 5 0.021) were highly predictive of a histologic response. Using SUV _max of 4.04 at week 5, SUV _max of 3.15 at week 10, and 60% decrease from baseline at week 10 as cutoff values, we determined that the respective sensitivities were 0.93, 0.93, and 0.79 and that the respective specificities were 0.53, 0.71, and 0.76. Conclusion: SUV _max on routine images at 5 or 10 wk and percentage change in SUV _max from baseline to week 10 were metabolic predictors of a histologic response in OS. These findings may be useful in the early identification of patients who are responding poorly to therapy and may benefit from a change in treatment.