In dogs, the metaphysis is the region of the bone most commonly affected by osteosarcoma.

In dogs, the metaphysis is the region of the bone most commonly affected by osteosarcoma.

• A. Epiphysis
• B. Diaphysis
• C. Periosteum
• D. Metaphysis

Answer: (D)

The question tests where bone tumors like osteosarcoma most often arise in dogs. Osteosarcoma originates from bone-forming (osteoblastic) cells, and the region with the most active osteoblastic activity and rich blood supply in a growing dog is the metaphysis—the area just next to the growth plate between the epiphysis and the diaphysis. This active endochondral ossification zone provides both the cellular environment and the vascular access that favor malignant transformation and rapid tumor growth. By contrast, the epiphysis is the joint end, the diaphysis is the shaft with relatively less osteoblastic turnover, and the periosteum is a surface membrane rather than a primary site of origin. Therefore, the metaphysis is the most common site for osteosarcoma in dogs.

The question tests where bone tumors like osteosarcoma most often arise in dogs. Osteosarcoma originates from bone-forming (osteoblastic) cells, and the region with the most active osteoblastic activity and rich blood supply in a growing dog is the metaphysis—the area just next to the growth plate between the epiphysis and the diaphysis. This active endochondral ossification zone provides both the cellular environment and the vascular access that favor malignant transformation and rapid tumor growth. By contrast, the epiphysis is the joint end, the diaphysis is the shaft with relatively less osteoblastic turnover, and the periosteum is a surface membrane rather than a primary site of origin. Therefore, the metaphysis is the most common site for osteosarcoma in dogs.