A new relative tumor sizing method in epi-metaphyseal osteosarcoma

BACKGROUND: The goal of this study was to develop a new method for determining tumor size to predict prognosis with high performance in osteosarcoma. METHODS: This study was approved by the institutional review board. We retrospectively reviewed 41 magnetic resonance (MR) images at diagnosis and 57 MR images after neoadjuvant chemotherapy from 59 patients with non-metastatic, high-grade extremity osteosarcoma, who had undergone surgery between October 1994 and October 2009. RESULTS: A new parameter of tumor axial ratio (TAR) was designed to normalize tumor size by dividing the absolute tumor axial size by the reference bone axial size (RBS) of the affected bone. RBS was defined using anatomical landmarks for each type of bone. Absolute tumor length (ATL), absolute tumor volume (ATV), and relative tumor volume (RTV) were comparatively analyzed. TAR was only significantly decreased after chemotherapy in the survival (P = 0.009) and metastasis-free (P = 0.018) group in the paired t-test. With the Kaplan–Meier method, significant differences in overall survival (log rank P = 0.004) and disease-free survival (Log Rank P = 0.009) were noted between decreased TAR after chemotherapy and increased TAR. After Cox regression analysis, TAR showed an odds ratios of 5.931 for survival (95% Confidence Interval [CI], 1.153–30.513) and 14.144 for metastasis (95% CI, 2.826–70.784), whereas ATL, ATV, and RTV showed no associations with these clinical variables. The AUC value of TAR was 0.713 (95% CI, 0.548 to 0.878) for survival and 0.759 (95% CI, 0.608 to 0.909) for metastasis. CONCLUSIONS: TAR is a novel sizing method with potential as a prognostic tool in osteosarcoma.