TO THE EDITOR: We read with interest the article by Franzius et al. (1) dealing with the prognostic significance of ¹⁸F-FDG and ^99mTc-methylene diphosphonate (MDP) uptake in primary osteosarcoma. The authors examined 29 patients and semiquantitatively measured ¹⁸F-FDG and ^99mTc-MDP uptake (average and maximum tumor-to-nontumor ratios [T/NT_av and T/NT_max, respectively]) using PET and bone scintigraphy at the time of diagnosis. We congratulate the authors on their excellent study. It showed that initial ¹⁸F-FDG T/NT_max values clearly discriminated between osteosarcoma patients with a high probability of overall and event-free survival and osteosarcoma patients with a poor prognosis. The authors did not observe a correlation between ^99mTc-MDP uptake and prognosis. These results agreed with the reports of another group (2), which could not find any significant relationship at any time between absolute radiopharmaceutical activity within the primary lesion and either disease progression or patient survival.

The evaluation of other parameters, such as quantification of perfusion or venous blood pool (vascular and soft-tissue factors), in 3-phase bone scintigraphy could have led to a more specific conclusion about prognosis. Former studies have already shown that the vascular factor is an important predictor of therapeutic response (3,4). A decrease in the tumor–to–blood flow ratio and extension were the most notable findings in responders to chemotherapy.

The study showed a significant correlation between ¹⁸F-FDG T/NT_max and prognostic outcome. However, it is unfortunate that transmission scanning was not performed in all cases and that consecutive standardized uptake values (SUVs) could not be evaluated sufficiently. This might have provided a prognostically valuable cutoff for SUVs.

On the other hand, the comparison of data using tumor-to-nontumor ratios and data using SUVs is limited because tumor-to-nontumor ratios are a less quantitative measurement of tumor ¹⁸F-FDG metabolism than are SUVs.

In conclusion, we expect that assessment of all available parameters (perfusion, blood pool, mineralization, and glucose consumption) would give the most reliable information for further patient management.