Among central osteosarcoma, periosteal osteosarcoma, and parosteal osteosarcoma, which is most common and most aggressive?

• A. Periosteal OSA
• B. Central OSA
• C. Parosteal OSA
• D. None of the above

Answer: (B)

The main idea here is that where the osteosarcoma arises within the bone strongly influences how it behaves. Central (intramedullary) osteosarcoma grows inside the marrow cavity and tends to be high-grade with rapid growth and early spread to the lungs, so it behaves aggressively. Because of this intramedullary location and the biology of these tumors, central osteosarcoma is the most common form and the most aggressive among the three listed.

In contrast, periosteal and parosteal osteosarcomas originate on the bone surface. They are generally encountered less frequently and tend to be lower in grade with slower progression and later metastasis, so they are less aggressive than the central type. Therefore central osteosarcoma best fits the description of being both most common and most aggressive.