The longest tumor diameter in one dimension as a predictor for skeletal metastasis in renal cell carcinoma

Renal cell carcinoma (RCC) comprises a diverse group of malignant neoplasms that have multifarious histopathological features and biological behavior. One-third of RCC patients develops skeletal metastasis with a poor 5-year survival rate. Data explaining how some of these tumors show sooner bony metastasis than expected is sparse. The objective of this study was to identify whether tumor size can act as a predictor of bony metastases among patients of RCC.

We retrospectively reviewed contrast enhanced computed tomography (CECT) scan and clinical records of 66 patients with RCC, who fulfilled specified inclusion criteria. Patients who had bony metastasis at the time of presentation were selected as case and those without skeletal metastasis were referred to as controls. Receiver operating characteristic (ROC) curve analysis was used to determine the appropriate cut-off value for tumor size, which was measured as the longest tumor diameter (LTD) in one-dimensional (1D).

Of the 66 patients selected, 30% developed bone metastasis. The tumor size of RCCs significantly correlated with the presence of skeletal metastasis in our study. None of the patients with 1D LTD <4.8 cm on CECT were found to have skeletal metastasis. ROC analysis revealed that the accuracy of the LTD in predicting bone metastasis was high with an area under ROC curve of 0.823. A cut-off value of 7.5 cm had a sensitivity of 78.9% and specificity of 80.9%.

The 1D LTD with a cut-off value of 7.5 cm, at the time of presentation is an important predictor of skeletal metastasis. The result of this study may have role in triage of patients into a subgroup which mandates more aggressive treatment and monitoring.