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.

Pathology

 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. The tumor is solid, hard, irregular ("fir-tree" 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 characteric 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. Presence of immature blood vessels (sarcomatous vessels lacking endothelial cells) favors the bloodstream metastasizing.

 

 Causes

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.

 

Symptoms

 Many patients first complain of pain that may be worse at night, and may have been occurring for some time. If the tumour 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).

 

 Genetics

 Hereditary syndromes of osteosarcoma have been identified:

     * Rothmund-Thomson Syndrome

    * RECQL4 gene mutations

    * RB1 gene mutations (also implicated in retinoblastoma)

    * Li-Fraumeni syndrome

 These syndromes are extremely rare within the Osteosarcoma diagnosis, and probably represent less than 0.5% of those diagnosed

 

Diagnosis

 Family physicians and orthopedists rarely see a malignant bone tumor (most bone tumors are benign). Thus, many patients are initially misdiagnosed with cysts or muscle problems, and some are sent straight to physical therapy without an x-ray.

 The route to osteosarcoma diagnosis usually begins with an x-ray, continues with a combination of scans (CT scan, PET scan, bone scan, MRI) and ends with a surgical biopsy. Much can be seen on films, but the biopsy is the only definitive proof that a bone tumor is indeed malignant or benign.

 The biopsy of suspected osteosarcoma should be performed by a qualified orthopedic oncologist. The American Cancer Society states: "Probably in no other cancer is it as important to perform this procedure properly. An improperly performed biopsy may make it difficult to save the affected limb from amputation."

 

Treatment

 Patients with osteosarcoma are best managed by a medical oncologist and an orthopedic oncologist experienced in managing sarcomas. Current standard treatment is to use neoadjuvant chemotherapy (chemotherapy given before surgery) followed by surgical resection. The percentage of tumor cell necrosis (cell death) seen in the tumor after surgery gives an idea of the prognosis and also lets the oncologist know if the chemotherapy regime should be altered after surgery.

 Standard therapy is a combination of limb-salvage orthopedic surgery and a combination of high dose methotrexate with leucovorin rescue, intra-arterial cisplatin caffeine, adriamycin, ifosfamide with mesna, BCD, etoposide, muramyl tri-peptite (MTP).

 Ifosfamide can be used as an adjuvant treatment if the necrosis rate is low.

 3-year event free survival ranges from 50% to 75%. and 5-year survival ranges from 60% to 85+% in some studies. Overall, 60-65% treated 5-years ago (2000) will be alive today. Osteosarcoma has one of the lowest survival rates for pediatric cancer despite chemotherapy's success in osteosarcoma of 6 chemotherapies, interferon-alpha, interleukin-2, and being the prototype of solid tumors in cancer.

 Treatment studies come from Children's hospital Boston, Memorial Sloan-Kettering, Children's Oncology Group, Italian Oncology Group, Japan, and MD Anderson in Texas.

 Fluids are given for hydration.

 Drugs like Kytril and Zofran help with nausea and vomiting.

 Neupogen, epogen, Neulasta help with white blood cell counts and neutrophil counts.

 Blood helps with anemia.

  

Prognosis

     * Prognosis is separated into three groups.

     * Stage I osteosarcoma is rare and includes parosteal osteosarcoma or low-grade central osteosarcoma. It has an excellent prognosis (>90%) with wide resection.

     * Stage IIb prognosis depends on the site of the tumor (proximal tibia, femur, pelvis, etc.) size of the tumor mass (in cm.), the degree of necrosis from neoadjuvant chemotherapy (beforeoperation chemotherapy), and pathological factors like the degree of p-glycoprotein, whether your tumor is cxcr4-positive. Her2-positive as these can lead to distant metastases to the lung. Longer time to metastases, more than 12 months or 24 months and the number of metastases and resectability of them lead to the best prognosis with metastatic osteosarcoma. It is better to have fewer metastases than longer time to metastases. Those with a longer length of time(>24months) and few nodules (2 or fewer) have the best prognosis with a 2-year survival after the metastases of 50% 5-year of 40% and 10 year 20%. If metastases are both local and regional the prognosis is different unfortunately.

     * Initial Presentation of stage III osteosarcoma with lung metastates depends on the resectability of the primary tumor and lung nodules, degree of necrosis of the primary tumor, and maybe the number of metastases. Overall prognosis is 30% or greater depending.

 

 

Canine Osteosarcoma

 

Risk Factors

 Osteosarcoma is the most common bone tumor in dogs and typically afflicts middle-age large and giant breed dogs such as Irish Wolfhounds, Greyhounds, German Shepherds, Rottweilers, and Great Danes. It has a ten times greater incidence in dogs than humans. A hereditary base has been shown in St. Bernard dogs. Spayed/neutered dogs have twice the risk of intact ones to develop osteosarcoma.

 Clinical Presentation

 The most commonly affected bones are the proximal humerus, the distal radius, the distal femur, and the tibia, following the basic premise "far from the elbow, close to the knee". Other sites include the ribs, the mandible, the spine, and the pelvis. Rarely, osteosarcoma may arise from soft-tissues (extraskeletal osteosarcoma). Metastasis of tumors involving the limb bones is very common, usually to the lungs. The tumor causes a great deal of pain, and can even lead to fracture of the affected bone.

 

Treatment and Prognosis

 Amputation of the leg is the initial treatment, although this alone will not prevent metastasis. Chemotherapy combined with amputation improves the survival time, but most dogs still die within a year. There are surgical techniques designed to save the leg (limb-sparing procedures), but they do not improve the prognosis. One key difference between osteosarcoma in dogs and humans is that the cancer is far more likely to spread to the lungs in dogs.

 Some current studies indicate that osteoclast inhibitors such as alendronate and pamidronate may have beneficial effects on the quality of life by reducing osteolysis, thus reducing the degree of pain as well as the risk of pathological fractures.

 

Osteosarcoma in Cats

 Osteosarcoma is also the most common bone tumor in the cat, although not as frequently encountered, and most typically affects the rear leg. The cancer is less aggressive in cats than in dogs, and therefore amputation alone can lead to a significant survival time. 

 

 

 

 

 

 

 

 

 

 

 

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