Incidence

Osteogenic sarcoma (Osteosarcoma)

Osteogenic sarcoma (OS) is an aggressive cancerous neoplasm arising from primitive transformed cells of mesenchymal origin that exhibit osteoblastic differentiation and produce malignant osteoid. It is the most common histological form of primary bone cancer.

Note! Two main types of cells in our bones help them stay strong and keep their shape:

v Osteoblasts help build up bones by forming the bone matrix (the connective tissue and minerals that give bone its strength).

v Osteoclasts prevent too much bone matrix from building up and help bones keep their proper shape. By depositing or removing minerals from the bones, osteoclasts also help control the amount of these minerals in the blood.

Like osteoblasts of normal bone, the cells that form this cancer make bone matrix. But the bone matrix of an OS is not as strong as that of normal bones.

Osteosarcoma derives from primitive bone-forming mesenchymal cells and is the most common primary bone tumor. OS occurs most frequently in adolescents, but there is a second incidence peak among individuals aged 60-65 and older.

Among childhood cancers, osteosarcoma occurs eighth in general incidence and in the following order: leukemia (30%), brain and other nervous system cancers (22.3%), neuroblastoma (7.3%), Wilms tumor (5.6%), Non-Hodgkin lymphoma (4.5%), rhabdomyosarcoma (3.1%), retinoblastoma (2.8%), osteosarcoma (2.4%), and Ewing sarcoma (1.4%).

Image 9.11 Predilections of osteosarcoma (Image by Mikael Häggström, 2008).

The incidence rates of childhood and adolescent osteosarcoma with 95% confidence intervals areas follows: Blacks, 6.8/year/million; Hispanics, 6.5/year/million; and Caucasians, 4.6/year/million. Osteosarcoma has a bimodal age distribution, having the first peak during adolescence and the second peak in older adulthood. The first peak is in the 10–14-year-old age group, coinciding with the pubertal growth spurt. This suggests a close relationship between the adolescent growth spurt and osteosarcoma. The second osteosarcoma peak is in adults older than 65 years of age; it is more likely to represent a second malignancy, frequently related to Paget’s disease.

There is a preference for origination in the metaphyseal region of tubular long bones. Most often it affects the proximal end of tibia or humerus, or distal end of femur. Osteosarcoma tends to affect regions around the knee in 60% of cases, 15% around the hip, 10% at the shoulder, and 8% in the jaw (Image 9.11).