Definition and Overview
Osteosarcoma is the most common type of cancer that develops in bone. It is aggressive and most commonly occurs in children and young adults between the ages of 10 and 30. Teens are the most commonly affected age group while people over the age of 60 are the least affected. It is a serious, life-threatening form of musculoskeletal cancer that commonly spread (metastasise) to the lungs.
There are different bones that make up the human body. These include flat bones (support and protect the vital organs such as the brain), long bones (make a framework for the muscles), and cell-forming bones (bone marrow). These bones are supported by two types of cells:
Osteoblasts – These cells originate from the bone marrow and form new bone made of bone collagen and other protein. They are found on the surface of the new bone and control calcium and mineral deposition.
Osteoclasts – These are large cells that dissolve the bone to prevent it from building up too much ensuring that it achieves and keeps its proper shape.
Osteosarcoma usually develops in the osteoblasts or growing bones. This explains why it most commonly affects teens that are having a growth spurt. The cancerous cells usually develop near the ends of the long bones such as the lower part of the thighbone, the upper part of the arm bone, and the upper part of the shinbone. In adults, the disease is commonly diagnosed in the jaw, hips, and shoulder.
Osteosarcoma can be either primary or secondary. It is classified as primary if it occurs as a result of an abnormality in bone development and secondary if it is caused by another condition. Osteosarcomas are further classified based on their appearance and location. They are called intramedullary if they develop in the medullary cavity of a long bone, juxtacortical if they are located on the other surface of the bone, and extraskeletal if they arise in soft tissues.
Causes of the Condition
The definitive causes of osteosarcoma and other cancers like chondrosarcoma, neuroblastoma, and leiomyosarcoma are yet to be established by doctors. Although it is known in the medical community as an “ancient disease”, this rare type of bone cancer is still not well understood. Some theorise that it is a result of DNA mutations causing healthy bone cells to reproduce very rapidly and form a tumour. DNA damage during the normal process of cellular division can be caused by prior radiation treatment, genetic predisposition, and underlying bone abnormalities such as Paget’s disease of the bone. Certain factors that can increase a person’s risk of developing osteosarcoma have been identified through specialised research. The following are often found among patients diagnosed with the disease.
Inherited syndromes, including retinoblastoma, Rothmund-Thompson syndrome, Li-Fraumeni syndrome (osteosarcoma syndrome), Bloom syndrome, Diamond-Blackfan anemia, and Werner syndrome
Previous radiation therapy for another type of cancer
Osteochondroma or Paget disease
Rapid bone growth
Osteosarcoma cancer produces noticeable symptoms early on allowing patients to seek medical attention during the early stages of the disease. These include:
A palpable lump
Bone or joint pain
Unexplained weight loss
Walking difficulties (if the tumour is in the leg bone)
Weak bones resulting in fractures
Increased pain with lifting
Patients with localised osteosarcoma have a wider range of treatment options and generally better prognoses. Thus, it is important for any unusual symptoms to be promptly reported to a physician for a diagnosis.
Who to See and Types of Treatments Available
Osteosarcoma is diagnosed with the use of imaging tests. Patients who complain of symptoms mention above usually undergo an x-ray, which is usually enough for an experienced radiologist to spot malignant tumour of the bone. To confirm the diagnosis and to determine the stage of the disease, additional tests are performed. These include:
Magnetic resonance imaging (MRI)
CT scan of the chest to rule out lung metastases
A biopsy is also performed to assess the tumour’s characteristics under a microscope. This helps doctors determine whether it is high or low grade.
Low-grade osteosarcomas, which only account for 1% of all cases and which usually occur in higher age group, are likely to grow and spread very slowly. High-grade osteosarcomas, on the other hand, are the exact opposite as they can grow and spread quickly.
Osteosarcoma, just like other types of cancer such as lymphoma (cancer of the lymph nodes), melanoma (skin cancer), and leukemia (cancer of the bone marrow), is treated with surgery followed by either chemotherapy or radiation therapy (adjuvant therapy). Patients with low-grade tumours typically undergo surgery first while those with high-grade tumours undergo chemotherapy sessions for up to three months to shrink the tumour before their surgery.
Malignant tumours are removed with a wide margin of healthy tissue around them to ensure that no cancer cells remain. Surgeons exhaust all means to ensure that in the process, the patient’s affected limb is spared to avoid long-term disability that can significantly affect their quality of life. The tissues that were removed during surgery are replaced with a metal implant or an allograph, or a combination of two. In severe cases where the cancer cells have affected a huge portion of the limb, surgeons perform an amputation.
Following surgery, patients undergo adjuvant therapy. During this process, a pathologist assesses the rate at which tumour cells die, which indicates how well the body responds to the therapy. Based on the pathologist’s assessment, new drugs can be used for chemotherapy or adjustments on patient’s radiation therapy will be made. Patients are continuously monitored throughout the duration of treatment with a focus on the function of their liver, heart, and kidneys. Thus, they undergo various imaging tests until their treatment has been completed.
Many factors can affect the outlook for patients with osteosarcoma following bone cancer treatment. These include:
The size and location of the tumour
Whether or not cancer cells have already spread to other areas of the body
How well the patient responds to therapies
Patients with high-grade osteosarcoma have a survival rate of approximately 70%. The survival rate for those whose disease has spread throughout the body is significantly lower. Meanwhile, patients who have successfully completed treatment are still at risk of recurrences or developing the condition again. A recurrent osteosarcoma can affect the same bone or other organs and tissues, such as the lungs. Thus, it is essential for patients to maintain their follow-up testing and examination schedules even after a long period of remission.
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Yang J, Yang D, Cogdell D, Du X, Li H, Pang Y, et al. APEX1 gene amplification and its protein overexpression in osteosarcoma: correlation with recurrence, metastasis, and survival. Technol Cancer Res Treat. 2010 Apr. 9(2):161-9.