What are osteolytic lesions in bone metastases?

• A. Fluid-filled areas causing bone destruction with a high fracture risk.
• B. Areas of new bone formation increasing density.
• C. Lesions that only affect cartilage.
• D. Lesions associated with increased bone growth.

Answer: (A)

Osteolytic lesions are bone-destroying areas created when cancer metastasizes to bone and stimulates the bone’s osteoclasts to resorb bone. This produces irregular, radiolucent (darker) cavities within the bone, indicating loss of bone structure. Because the bone is weakened where resorption is active, the risk of pathologic fracture is high, even with minor trauma, and patients often report bone pain. This pattern contrasts with osteoblastic (sclerotic) metastases, which stimulate new bone formation and appear as denser, white regions on imaging. Cartilage involvement isn’t the primary feature of these metastases, and they don’t reflect increased bone growth. The mechanism involves tumor cells releasing factors like RANKL that activate osteoclasts, leading to a vicious cycle of bone destruction and tumor growth. Management focuses on pain control and inhibiting osteoclast activity (for example with bisphosphonates or denosumab), along with local control and stabilization as needed to prevent fractures.