A 22-year-old woman undergoes excision of a symptomatic osteochondroma of the distal femur. She asks about the risk of the lesion turning malignant. The correct statement regarding malignant transformation of osteochondroma is:

• A Transformation, when it occurs, is almost always into osteosarcoma
• B Risk is equal in solitary and multiple lesions, approximately 10 percent in both
• C Risk is under 1 percent in solitary lesions but rises to about 5 to 10 percent in hereditary multiple osteochondromas ✓
• D Transformation risk persists throughout life and peaks after the age of 60 years

Explanation

Solitary osteochondromas carry a very low malignant transformation risk of less than 1 percent, while in hereditary multiple osteochondromas (multiple hereditary exostoses, autosomal dominant EXT1 or EXT2 mutations) the cumulative risk rises to roughly 5 to 10 percent. The resulting malignancy is almost always a secondary peripheral chondrosarcoma arising from the cartilage cap, not osteosarcoma, which eliminates option A. Transformation typically occurs in adulthood when a previously quiescent cap thickens or grows.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.