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Osteosarcoma is the most common type of malignant bone cancer, accounting for 35% of primary bone malignancies. There is a preference for the metaphyseal region of tubular long bones. 50% of cases occur around the knee. It is a malignant connective (soft) tissue tumor whose neoplastic cells present osteoblastic differentiation and form tumoral bone.
Osteogenic Sarcoma is the 6th leading cancer in children under age 15. Osteogenic Sarcoma affects 400 children under age 20 and 500 adults (most between the ages of 15-30) every year in the USA. Approximately 1/3 of the 900 will die each year, or about 300 a year. A second peak in incidence occurs in the elderly, usually associated with an underlying bone pathology such as Paget’s disease, medullary infarct, or prior irradiation. Although about 90% of patients are able to have limb-salvage surgery, complications, such as infection, prosthetic loosening and non-union, or local tumor recurrence may cause the need for further surgery or amputation.
The tumor may be localized at the end of the long bones. Most often it affects the upper end of tibia or humerus, or lower end of femur. it tend to affect area around the knee in 60% of cases, 15% around the hip, 10% at the shoulder, and 8% in the jaw. The tumor is solid, hard, irregular (“fir-tree,” “moth-eaten” or “sun-burst” appearance on X-ray examination) due to the tumor spicules of calcified bone radiating in right angles. These right angles form what is known as Codman’s triangle. Surrounding tissues are infiltrated.
Microscopically: The characteristic feature of osteosarcoma is presence of osteoid (bone formation) within the tumour. Tumor cells are very pleomorphic (anaplastic), some are giant, numerous atypical mitoses. These cells produce osteoid describing irregular trabeculae (amorphous, eosinophilic/pink) with or without central calcification (hematoxylinophilic/blue, granular) – tumor bone. Tumor cells are included in the osteoid matrix. Depending on the features of the tumour cells present (whether they resemble bone cells, cartilage cells or fibroblast cells), the tumour can be subclassified.
The causes of osteosarcoma are not known. Questions remain about whether radium, or fluoride, in drinking water can act as “environmental triggers” for increasing the incidence of the disease. A low selenium or Vitamin D3 level or a high level of inflammation, as measured by interleukin-6, interleukin-8, or Nf-kB, Tumor Necrosis Factor Alpha may have a significant role as tumor suppressors and tumor initiators respectively. Recent studies show that an increased level of c-Fos can lead to osteosarcoma. The study that showed this result was done on transgenic mice in which the Fluid Sheer Stress (FSS) was increased to increase the number of osteoblast. Since c-Fos is ubiquitous in its over expression it can not only increase the osteoblast resulting in the symptoms of osteosarcoma. Therefore it is recently believed that a biological effect that may cause osteosarcoma is an error in the molecular pathway that controls c-Fos, causing an overexpression with no other counter stimuli to stop over production.
Many patients first complain of pain that may be worse at night, and may have been occurring for some time. If the tumor is large, it can appear as a swelling. The affected bone is not as strong as normal bones and may fracture with minor trauma (a pathological fracture).