In children, teens, and young adults, osteosarcoma usually starts in areas where the bone is growing quickly, such as near the ends of the leg or arm bones: Most tumors develop in the bones around the knee, either in the lower part of the thigh bone (distal femur) or the upper part of the shinbone (proximal tibia).

Does bone cancer start somewhere?

Cancers that start in the bones are called primary bone cancers. These types of cancers aren't very common. Most of the time when an adult with cancer is told they have cancer in the bones, the doctor is talking about a cancer that started somewhere else and then spread to the bones. This is called bone metastasis.

Where does osteosarcoma spread first?

Most often it spreads to the lungs, but it can also spread to other bones, the brain, or other organs. About 1 out of 5 osteosarcomas have spread already when they are first diagnosed.