Validation of the Bone-RADS (Bone Reporting and Data System) Score for Predicting Risk of Malignancy

Background: Bone-RADS (Bone Reporting and Data System) is a consensus guideline by the American College of Radiology to assist in the risk stratification of lytic bone lesions. A score is calculated using 5 radiographic factors and a history of primary malignancy. The purpose of this study was to externally validate the Bone-RADS scoring system. Methods: This retrospective review examined radiographs from January 1, 2021, to December 31, 2021. Radiographs were identified via a keyword search for “lucent,” “osteolytic,” or “lytic” in extremity radiograph reports. All radiographs were initially read by a musculoskeletal radiologist. Radiographs of skeletally immature patients, lesions in a bone other than a long bone, primary soft-tissue masses, and negative/normal radiographs were excluded. Radiographs were independently scored on the basis of the Bone-RADS system by 4 reviewers. In the absence of a biopsy, a lesion was considered benign if it remained stable for 2 years on radiographs. Scores were correlated with final diagnoses to calculate the rates of malignancy and malignant transformation. Results: Of 1,108 screened radiographs, 423 were eligible. The mean age of the patients was 62 years and 49% were male. A higher Bone-RADS score was associated with a malignant diagnosis (p < 0.001), with an odds ratio of 9.7 (95% confidence interval [CI], 6.2 to 14.9) per 1-unit increase in the score. A higher margin score (p < 0.001), endosteal erosion (p < 0.001), a pathologic fracture (p < 0.001), and a soft-tissue mass (p = 0.02) were associated with increased risk of malignancy. The mean inter-rater agreement (weighted kappa) was 0.52, the inter-rater mean absolute deviation (MAD) was 0.37, and the intra-rater MAD was 0.27. Sensitivity was 97.1% (CI, 94.4% to 98.5%), specificity was 67.4% (CI, 59.3% to 74.5%), positive predictive value was 85.2% (CI, 80.9% to 88.7%), and negative predictive value was 92.4% (CI, 85.7% to 96.1%). Conclusions: The Bone-RADS scoring system demonstrated moderate diagnostic performance for malignancy risk stratification of lytic bone lesions, with high sensitivity and reproducible binary classification of possibly benign versus malignant. Although inter-rater agreement for the 4-tier score was only moderate, clinically relevant benign-versus-malignant categorization demonstrated higher inter- and intra-rater agreement. These findings support Bone-RADS as a practical triage framework based on musculoskeletal imaging of lytic bone lesions. Level of Evidence: Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.