Investigating possible predictors of malignant transformation of osteochondroma: a retrospective cohort study with an illustrative case report.

Objective: To investigate the relationship between cartilage cap thickness, osteochondroma subtype (pedunculated vs. sessile), patient age, and multiple hereditary exostoses (MHE) diagnosis with malignant transformation of osteochondromas.

Methods: A single-institution retrospective study of patients who underwent surgical excision of one or more osteochondromas between 1983 and 2025 was conducted. The relationship between cartilage cap thickness, osteochondroma subtype (pedunculated vs. sessile), patient age, and MHE diagnosis with malignant transformation was investigated.

Results: Among 1138 pathology-confirmed osteochondromas, 1097 (96.4%) were benign osteochondromas and 41 (3.60%) underwent malignant transformation. In tumors with a pathology-measured cartilage cap (n = 411), benign tumors (n = 397) had a smaller median cap size than malignant lesions (0.3 cm [IQR: 0.2-0.6 cm] vs. 3.15 cm [IQR: 1.93-4.78 cm]; p < .0001). Among 27 malignant cases with preoperative imaging, 63% were sessile and 37% pedunculated. Patients with benign tumors were younger than those with malignant transformations (27.1 ± 15.9 vs. 37.8 ± 12.2 years; p < .0001). Patients with MHE had a greater incidence of malignant transformation compared to patients without (17% vs. 1.98%) (p < .0001). 137 MRIs and 37 CTs were compared to pathology measurements, yielding a concordance correlation coefficient of 0.80 and 0.92, respectively. The sensitivities and specificities were 29% and 91% for MRI and 67% and 94% for CT, respectively.

Conclusion: A thicker cartilage cap, older age, and confirmed MHE diagnosis were each significantly associated with a higher rate of malignant transformation. Multidisciplinary teams should factor in a patient's clinical presentation and past medical history in addition to the tumor characteristics in deciding the proper course of treatment.