Osteosarcoma is a type of aggressive bone cancer that primarily affects the long bones, such as those in the arms and legs. It is most commonly diagnosed in adolescents and young adults, often during periods of rapid growth. The exact cause of osteosarcoma is not well understood, but genetic factors and previous radiation therapy are known risk factors. Symptoms typically include localized pain and swelling, and the diagnosis is confirmed through imaging studies and biopsy. Treatment usually involves a combination of surgery and chemotherapy, with the goal of removing the tumor and preventing metastasis.