Which statement about the relationship between reactive bone and tumor bone in osteosarcoma is true?

• A. Reactive bone may be present between tumor trabeculae if cortex breached
• B. Reactive bone is never present
• C. Osteosarcoma lacks osteoid production
• D. Reactive bone always dominates

Answer: (A)

In osteosarcoma, malignant osteoblasts produce osteoid that becomes tumor bone, while the surrounding host bone can react to tumor invasion. If the cortex is breached by the tumor, the periosteum and adjacent bone may lay down new bone between the tumor trabeculae, leading to reactive bone formation in that zone. This reactive bone reflects the host response, not the tumor’s osteoid, and its presence between tumor trabeculae is compatible with cortex involvement. The key is that tumor osteoid production defines osteosarcoma, but reactive bone from the host can also appear, especially when the cortex is compromised. Reactive bone is not always present, and it does not mean the tumor osteoid is absent or that reactive bone “dominates.”