PET/CT provides osteosarcoma prognosis
Osteosarcoma accounts for approximately 35 percent of all bone malignancies and is the sixth most common type of cancer in children; as such, prognostic indicators play a great role in the therapeutic decision process. By measuring the maximum standardized uptake value (SUVmax) and total lesion glycolysis (TLG) using FDG-PET/CT, clinicians may be better able to predict outcome, and determine the appropriate course of treatment, for osteosarcoma patients.

“Because prognostic indicators influence therapy, the purpose of our study was to assess whether TLG and SUVmax are predictive of tumor necrosis after neoadjuvant chemotherapy in patients with osteosarcoma and to evaluate the performance of both of these parameters in the prediction of progression-free and overall survival,” wrote researchers from the University of Texas M.D. Anderson Cancer Center in Houston.

The team, whose work was published in the March issue of the Journal of Nuclear Medicine, reviewed 31 consecutive patients who underwent FDG PET/CT before and after chemotherapy, followed by tumor resection.

Integrated PET/CT systems were used to acquire imaging data (Discovery ST, STe, or RX; GE Healthcare). The scientists reported that whole-body examinations were performed from the level of the vertex of the skull or orbits through the upper thighs or lower legs or toes, depending on the location of the primary tumor.

Two radiologists, experienced in PET/CT interpretation, measured the SUVmax and TLG for the 31 patients on pre-chemotherapeutic and post-chemotherapeutic PET/CT examinations, using an Advantage workstation (GE Healthcare). Univariate Cox regression was used to analyze for relationships between covariates of interest (SUVmax before and after chemotherapy, change in SUVmax, TLG before and after chemotherapy, change in TLG and tumor necrosis) and progression-free and overall survival. Logistic regression was used to evaluate tumor necrosis.

Progression-free survival was defined as the number of days after the initiation of chemotherapy until disease recurrence, either pulmonary metastases or local recurrence, or death.

Fused 18F-FDG PET/CT images of 61-year-old man with high-grade conventional osteosarcoma of proximal tibial metaphysis. Coronal (A) and axial (B) images of tumor before chemotherapy demonstrate SUVmax and TLG values of 33.7 g/mL and 895.1 g, respectively. Though area of 18F-FDG uptake has decreased on coronal (C) and axial (D) images after completion of chemotherapy, only mild reduction in SUVmax (23.9 g/mL) and TLG (553.0 g) is seen. As predicted by pre- and post-chemotherapeutic PET/CT values, pulmonary metastases developed 247 days after initiation of chemotherapy and patient succumbed to his disease 118 days later. Image and caption courtesy of SNM.
High SUVmax before and after chemotherapy was associated with worse progression-free survival, the researchers reported. They noted that good overall and progression-free survival was associated with a tumor necrosis greater than 90 percent. A tumor necrosis greater than 90 percent was most strongly associated with a decrease in SUVmax.

“Many of our findings, such as the association between tumor necrosis and outcome and the association of worse survival with high metabolic activity in the chemotherapy-naive tumor and with high metabolic activity after chemotherapy, all confirm the conclusions of prior studies that 18F-FDG PET accurately reflects response of osteosarcoma to chemotherapy,” the authors wrote.

A notable feature of the study is that it is the first to meaningfully evaluate TLG in patients with osteosarcoma.

“Unlike SUV, which is a measurement of metabolic activity per body weight, TLG evaluates metabolic activity throughout the volume of the tumor (SUV average multiplied by tumor volume) above a minimum threshold designed to exclude background activity,” the authors wrote.

Although the SUVmax measurement demonstrated a larger number of more strongly significant covariates, the researchers were able to demonstrate that the change in TLG in patients from pre- to post-chemotherapeutic examinations was a predictor of progression-free survival. In addition, their work showed that high TLG in the chemotherapy-naive tumor was associated with poor overall survival in their series of patients.

“Although the results suggest that SUVmax is a stronger indicator than is TLG, we are awaiting large prospective studies to more fully assess which of the two methods of measuring 18F-FDG uptake is the optimal predictor of survival,” the authors wrote.