Tumor volume change as a predictor of chemotherapeutic response in osteosarcoma.

The change in osteosarcoma tumor volume after preoperative adjuvant chemotherapy and its relationship to the histopathologic response was investigated using various reproducible volumetric methods. Tumor volume was measured before and after chemotherapy in 41 patients with osteosarcoma using an ellipsoid formula in plain radiography and magnetic resonance imaging and three-dimensional magnetic resonance imaging measurement. Based on intraobserver and interobserver variability for the volumetric measurements of each method, three-dimensional magnetic resonance imaging measurement was the most reproducible. In three-dimensional magnetic resonance measurements, the correlation of the histopathologic response with absolute and relative total tumor volume changes and extraosseous volume change were significant. The good responder group showed a greater reduction in tumor volume after chemotherapy, although there was no significant difference in pretreatment tumor volume between the good and poor responder groups. The group with a decreased or stable tumor volume represented a good histopathologic response with a sensitivity of 85%, specificity of 76%, and positive predictive value of 88%. The change in tumor volume of osteosarcoma measured by three-dimensional magnetic resonance imaging could predict histopathologic response after three cycles of neoadjuvant chemotherapy.