Review Question - QID 219356

A more central location (pelvis/hip) of an osteochondroma is a risk factor for secondary transformation into a chondrosarcoma.

Osteochondromas are relatively common, benign chondrogenic tumors derived from aberrant cartilage about the perichondral ring. Most are asymptomatic, but they can present a mass causing mechanical symptoms locally or neurovascular compression. A very small number of osteochondromas may transform secondary chondrosarcoma, which are usually low-grade and have good survival rates and low local recurrence rates. A diagnosis of multiple hereditary exostoses (MHE), central location, and older age have been correlated with an increased risk for transformation. Secondary chondrosarcomas are typically treated with wide surgical resection alone.

Lin et al. published a review on secondary chondrosarcomas in JAAOS, noting that it originates from a pre-existing cartilaginous lesion. They discuss that a sudden increase in the size of the cartilage cap is a concerning sign of malignant transformation; however, there is no strict cutoff for cartilage cap thickness with regard to diagnostic criteria. Most of the time, secondary chondrosarcoma is low/intermediate grade, and the prognosis is good, without distant metastasis being common; however, those with secondary chondrosarcoma of the pelvis have worse outcomes and higher risk for recurrence.

Ahmed et al. looked at 107 patients with secondary chondrosarcoma, noting a male preponderance with long bone predilection. Radiologically, irregularity of the tumor margin, inhomogeneous mineralization, and associated soft tissue mass were signs of transformation. Local recurrence rates were 16% and 17.5% at 5- and 10-years, respectively, while mortality rates were 1.6% and 4.8% at 5- and 10-years.

Staals et al. looked at the transformation of osteochondromas to dedifferentiated chondrosarcomas. The pelvis and the femur were the most common locations for this to occur. Survival rates for these patients were much lower than those with low-grade secondary chondrosarcoma, averaging 47% and 29% at 5- and 10-years, respectively.

Incorrect Answers:
Answer 2: The morphology (sessile vs. pedunculated) of the osteochondroma does not correlate with the risk for transformation to secondary chondrosarcoma.
Answer 3: Multiple osteochondromas (multiple hereditary exostosis) slightly increase the risk of transformation to secondary chondrosarcoma.
Answer 4: Increased age increases the risk for malignant transformation.
Answer 5: A cartilage cap >2-3mm in adult patients is concerning for potential transformation to chondrosarcoma.