What is Osteosarcoma?

Osteosarcoma is the most common type of cancer affecting the bone and involves abnormal osteoblast cells that are responsible for the construction of bone.

Children and young adults are most likely to be diagnosed with the disease, particularly around the age of adolescent growth spurts during puberty when the bones grow more quickly.

Epidemiology

The overall incidence of osteosarcoma in the United States is 400 cases per year, which equates to approximately 1 per 800,000 people. Individuals with darker skin have a slightly higher risk of being affected by osteosarcoma and males are more inclined to the condition than females.

The disease is very rare in young children but the incidence increases dramatically when individuals reach the growth spurts related to adolescence. The peak incidence occurs between the age of 15 and 19, with 8.5 cases per million per year.

Of those patients that are diagnosed with the disease, the five-year survival rate is approximately 63%, with a more positive prognosis noted in females than males.

Signs and Symptoms

The majority of tumors develop in the distal femur or the proximal tibia, the bones near the knee. Another common site is the proximal humerus, the bone near the shoulder. Osteosarcoma can present in any bone in the body, however.

Most patients experience signs of the disease for several weeks or months before they seek medical advice. The most common symptom is pain, which becomes more evident with physical activity. Due to the non-specificity of the symptoms, individuals often think the pain may be due to growing or previous physical trauma.

Upon physical examination, specific symptoms that may be noted in patients with osteosarcoma include mass around tumor site that may be tender or warm and decreased range of motion of affected joint.

The may be involvement of the lymph node and respiratory system in more advanced cases, but this is not seen in the majority of cases.

Telangiectatic is a specific subtype of osteosarcoma that is usually linked to a pathologic bone fracture. The pain and possible swelling in the area may cause difficulty of movement, leading to a limping gait.

Subtypes

Cases of osteosarcoma can be classified according to their appearance on an X-ray image or microscopic evaluation. The different subtypes (high-grade, intermediate-grade and low-grade) provide valuable information about the prognosis of the condition.

High-grade osteosarcomas are the fastest growing and are associated with a poorer prognosis. Their appearance under a microscope is distinct from that of normal bone cells, due to the quickly dividing cells. There are several subtypes of high-grade osteosarcomas, including:

• Osteoblastic
• Chrondroblastic
• Extra-skeletal
• Fibroblastic
• Juxtacortical high grade
• Pagetoid
• Post-radiation
• Small cell
• Telangiectatic

Intermediate-grade osteosarcomas are the least common type and exist between low and high-grade in severity. Juxtocortical intermediate grade is a subtype of this grade.

Low-grade osteosarcomas are associated with the most positive prognosis and grow slowly in comparison to the other grades of osteosarcoma. When viewed under a microscope, the cells look similar to normal bone cells and have few cells undergoing replication. Subtypes of this grade include juxtacortical low-grade and intramedullary well differentiated.

References

• http://emedicine.medscape.com/article/1256857-overview
• http://www.cancer.org/cancer/osteosarcoma/detailedguide/osteosarcoma-what-is-osteosarcoma
• http://sarcomahelp.org/osteosarcoma.html
• http://radiopaedia.org/articles/osteosarcoma