A mother drops off her $15-$year$-$old son at soccer practice. He plays for a traveling team, and she is headed to the grocery store to do some shopping while he is occupied. While at the store, she receives a telephone call from the coach, telling her that her son was kicked just below the knee, causing him to fall to the ground. He was wearing his shin guards but complains that it hurts too much to walk. The mother turns around and heads back to the soccer field. When she arrives, her son is sitting on the bench with ice on his leg. The coach and a teammate help her get him into the car, and she drives him to the emergency department. An x$-$ray image shows a fracture near the knee with subluxation.

$1.$ Attempts at closed reduction are unsuccessful; consequently, the young man is taken into surgery. At the completion of the procedure, the orthopedic surgeon talks with the family. The repair was more extensive than the surgeon had initially expected. Near the site of the break, a tumor was found. Based on the young man$$s age, the tumor is most likely what type? Explain why