Osteoblasts are nothing but bone forming cells (‘osteo’= bone & ‘blasts’= forming cells). When they start to undergo too much proliferation and become neoplastic, they form a malignant tumour called Osteosarcoma. Osteosarcoma is characterized by immature bone or osteoid tissue formed by neoplastic cells. However, fibrous or cartilaginous tissue may also co-exist or even predominate.
What are the causes of osteosarcoma ?
Certain factors such as exposure to ionizing radiation, episode of trauma, particular genetic alterations, pre-existing bone diseases like Paget’s disease of bone or fibrous dysplasia, and some viral infections incline the bone to the development of osteosarcoma, but none of them are the actual causative agents of the tumour.
It is also known now that cytotoxic chemotherapy and radiotherapy for other diseases can lead to the development of secondary osteosarcoma.
Genetically, patients affected with syndromes, for instance hereditary retinoblastoma, Li-Fraumeni syndrome, and the Rothmund-Thomson syndrome are susceptible to osteosarcoma. All these disorders have certain genetic alterations which contribute to tumour development. Numerous carcinogens (cancer-causing environmental factors) and oncogenes (genes which turn on tumour cells) have been proposed, such as mutations in the p53 tumour suppressor gene.
What are the clinical features of osteosarcoma ?
Age: It is the most commonly seen primary malignant bone tumour affecting the younger age group. Osteosarcoma has a bimodal peak incidence. The peak of the disease incidence correlates with the adolescent growth spurt.
Site: They arise predominantly in the long bones, occasionally in the axial bones, and seldom in the soft tissues. The classic or so-called conventional osteosarcoma develops basically in the metaphysis of long bones. It has a partiality for occurring in the knee area, that is either the lower thigh or upper shin bone. The second most common site is the proximal humerus, or that part of the arm that articulates with the shoulder. However, osteosarcoma has been known to occur in every bone.
Clinical presentation of osteosarcoma: In Osteosarcoma, the most common presentation is pain at site. This is generally worsened by physical exertion. There may be pain at nights as well. Any persistent bone pain, occurring even at night, should be examined by your doctor. Quite a few of the patients link the pain to a traumatic episode. Local tenderness, a palpable mass, painful joint movement, a limp, a limited range of movement & fever can also be noted. Primary bone cancer is sometimes revealed when a bone that has been damaged by cancer fractures after even a slight trauma.
They are aggressive tumours, known to destroy the normal bone in the area they occur, invading surrounding soft-tissue, and have a high metastatic potential, or the tendency to spread elsewhere in the body, mostly to the lungs.
What are the types of osteosarcoma?
There are several different types of osteosarcoma, namely the osteoblastic type, the chondroblastic type and also the fibroblastic osteosarcoma. In addition, there are also other rarer subtypes seen, namely the parosteal, periosteal, telangiectatic and small cell osteosarcoma.
How is an osteosarcoma diagnosed ?
The main modalities used in the identification and diagnosis of osteosarcoma are :
- Radiography for detecting the bone lesion : to establish preliminary diagnosis of osteosarcoma, to determine the location of the primary tumour and to detect if there is metastasis to the other parts of the body.
The radiographic appearance is changeable and can vary from lytic, to sclerotic, to mixed forms. In the mixed pattern, both bony destruction as well as new bone formation are found.Characteristic radiographic findings in osteosarcoma are basically the sunburst pattern (it is due to extension of tumour, its mineralization, and arrangement of radiating spicules), or the Codman’s triangle (periosteal elevation on either side of the lesion), in the tumour area. - MRI and bone scintigraphy : MRI is used to investigate the tumour extent, to organize for the location of biopsy and surgery, and to recognize any potential skip lesions. Scintigraphy (nuclear bone scan) with technetium-99m demonstrates an augmented uptake in the main tumour area corresponding with new bone forming and increased blood supply in the tumour.
- CT scans : These are used to detect metastasis. CT of the chest and abdomen is performed to identify any organ metastases. In recent years, micro CT is being used to view and analyze the microstructure of diseased tissue and detection of even minute, millimetre- sized tumours.
- Positron emission tomography (PET) : This is a significant nuclear imaging modality. The most commonly used tracer in PET is fluorine-18 fluorodeoxyglucose (F-18 FDG). It is basically a glucose analogue and is utilized by the cell’s glucose transporters. This marker accumulating in tumour areas is a pointer of great metabolic activity.
- Laboratory Investigations : Antigen-antibody testing: Serum IgM antibody level to tumour associated antigens like angiogenin (ANG-IgM) is a helpful diagnostic marker for osteosarcoma and lung metastases.
- Histopathological Investigations : Histopathology and immunohistochemistry are requisite for confirmation of osteosarcoma in the biopsied tissues. Finally, histopathologic methods are the end line of the diagnostic options.
The bone tissue that is found in the tumour is neoplastic. It is not formed by normal osteoblasts, but by tumour osteoblasts. The osteoblasts seen are pleomorphic and anaplastic.
How is an osteosarcoma treated ?
Most people with an osteosarcoma will need to have a combination of different treatments. The three basic modalities for cancer treatment include surgery, chemotherapy and/or radiotherapy, and now, even immunotherapy.
Surgery is a primary part of treatment and is used to eradicate the tumour from bone. If surgery is difficult, then radiotherapy may be used instead. Chemotherapy is used for most people with an osteosarcoma. It is often given to shrink the tumour before surgery.
- Surgery : Complete surgical resection of the tumour is performed by amputation of the limb, or if possible, limb-sparing salvage approach,that is removal of the tumour whilst sparing the limb. The aim of the surgery must be complete tumour removal including the reactive zone with a wide margin of normal tissue to avoid local recurrence and improve overall survival.If limb salvage is not possible, amputation or ablation of the limb may be performed. Currently, most patients with long bone osteosarcoma are treated by resection with wide margins, yet saving the limbs. However, it is important to keep in mind that limb-saving surgery bears an elevated risk of local recurrence as compared to amputation.Limb-sparing surgery consists of total removal of the tumour and limb reconstruction to restore motor function. The bones and joints that have been cut by surgery will have to be replaced by other materials and devices.
- Chemotherapy : Chemotherapy is the use of anti-cancer (or cytotoxic) drugs to annihilate cancer cells. It is a significant treatment for osteosarcoma as it augments surgical treatment. It is typically given prior to surgery to shrink outsized tumours in order to avert amputation. Neoadjuvant chemotherapy regimens and postoperative chemotherapy should be administered to control local tumour recurrence, prevent tumour metastases and micrometastases.
- Radiotherapy : Radiotherapy treats cancer by using radiation to destroy the cancer cells, whilst trying to spare normal unaffected cells. Radiotherapy is often used after surgery but may also be a primary treatment option wherever surgery is difficult or not possible. Radiotherapy has its own side effects such as reddening of skin, loss of hair and tiredness.
These side effects will have to be tolerated or treated, depending on their severity. - Immunotherapy : Immunotherapy is basically treating the disease by altering, enhancing, or suppressing the body’s immune system. Along with the early development of chemotherapy, immunotherapy also started developing and now it is yielding far better encouraging results.
The active agents of immunotherapy are collectively called immunomodulators. They are an assorted array of natural preparations, synthetic preparations or recombinant ones. These substances include cytokines, interferons, and bacterial based cellular membrane fractions and are already licensed for use in patients.
Immunotherapy is the future treatment choice in managing osteosarcoma.
What is the follow-up required after the treatment of osteosarcoma ?
After your treatment is completed, you will require regular check-ups by your doctor and x-ray examination. The radiographic & advanced imaging techniques are non-invasive techniques with diagnostic capability and are to be used for follow-up after surgery and to locate potential sites of metastasis. These check-ups will have to continue for several years. If you have notice any problems or recent symptoms, inform your doctor, as soon as possible.
How to find and reach cancer specialists for osteosarcoma treatment ?
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Disclaimer: The content provided here is meant for general informational purposes only and hence SHOULD NOT be relied upon as a substitute for sound professional medical advice, care or evaluation by a qualified doctor/physician or other relevantly qualified healthcare provider.
