What is the key difference in tumor location between osteosarcoma and Ewing's sarcoma?

• A. Osteosarcoma: end of long bones involved; Ewing: middle of long bones
• B. Ewing: end of long bones; Osteosarcoma: middle of long bones
• C. Osteosarcoma: ends; Ewing's: ends
• D. Both involve the ends of long bones equally

Answer: (A)

The key idea is where along the bone these tumors typically arise. Osteosarcoma most often starts in the metaphysis, the ends of long bones near the growth plate (often around the knee). Ewing’s sarcoma most often involves the diaphysis, the middle portion of long bones (and it can extend to the pelvis). So the pattern you’re looking for is osteosarcoma at the ends and Ewing’s in the middle, which matches the statement that osteosarcoma involves the ends while Ewing’s involves the middle. The other described patterns—placing Ewing’s at the ends or saying both ends are equally involved—don’t fit the common distribution.