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BONE TUMORS

Primary tumors of the bone account for about 2% of all childhood cancers. The two major types of primary bone tumors are osteosarcoma and Ewing sarcoma.

OSTEOSARCOMA

EPIDEMIOLOGY
The incidence of osteosarcoma is approximately 3 million in whites and 2.5 million in blacks. The cause is unknown. It is the second most common tumor seen in adolescent and young adults. Most children present between the ages of 15 and 19 years. It is thought to correlate with the period of rapid growth when an adolescent matures into a young adult. This period is also associated with growth sprout. Some genetic factors have been associated with the development of osteosarcoma. These include retinoblastoma, and Li-Fraumeni syndrome. Environmental factors include exposure to previous radiation.

SYMPTOMS
It presents as pain and swelling in the area of tumor. There is also a decrease range of motion in the bone involved. Sometimes it is picked up on X-ray studies performed in the work-up of a fractured bone. The bones usually affected are the long bones of the legs. The lower end of the femur (long bone in the thigh) is the commonest site of presentation (53%). Other sites are upper end of tibia (leg bone) (26%), Humerus (upper arm bone) (12%), fibula (outer leg bone) (5%), Scapula (upper back bone) (1%) and the ileum (hip bone) (1%).

DIAGNOSIS
This can be suspected from the history presented to the doctor and from the findings obtained on physical examination of the patient. Some tests need to be done to confirm this diagnosis. These tests include:

  1. X-rays of the affected bones. If a tumor is suspected then an MRI or CT scan of the bone should be done.
  2. Bone scan to find out if other bones are affected.
  3. A chest CT scan is also required because this tumor tends to spread to the lungs.
  4. Blood test to obtain blood count and to check blood chemistry.
  5. Biopsy of the tumor. The same orthopedic surgeon who will be performing the definitive surgery during treatment should ideally do this.

TREATMENT
Management requires a multidisciplinary approach including surgery, anesthesia, social service, physical therapy and chemotherapy, and the recommendation therefore, is that a center with the appropriate facilities and experienced staff handle such complicated management . Radiotherapy is generally not used to treat osteosarcoma because the tumor cells are not sensitive to radiation.

SURGERY
The two main types of surgery done for osteosarcoma in the bones of the legs and arm are:

  1. Amputation in which the affected limb is removed completely.
  2. Limb salvage surgery in which the tumor is removed and a prosthesis is then placed in the limb to help limit the deformity and also to maintain adequate function of the limb.

The decision as to which procedure is best depends on the size of the tumor, its location, involvement of surrounding nerves and blood vessels, presence or absence of a non-healing pathological fracture, infected biopsy site and possibility of contamination of surrounding tissue with tumor cells at the time of biopsy. In tumors involving non-extremity bones, the tumor is removed as a block. This is called en-bloc resection. Amputation is the standard treatment for tumors involving the long bones of the arm and legs. However with the advent of chemotherapy, it is now possible to shrink this tumor to a smaller size with chemotherapy prior to surgery. Thus at surgery, a limb-sparing procedure is done whereby the tumor along with some normal bone is removed and the defect is replaced by a prosthetic device.

Definitive surgery now generally done after the patient has received a course of chemotherapy. This helps determine the response of the tumor to chemotherapy. If there is evidence of spread to the lungs these lesions have to be removed surgically.

CHEMOTHERAPY
Chemotherapy can be given prior to surgery (neoadjuvant chemotherapy) or after surgery (adjuvant chemotherapy). The advantages of neoadjuvant chemotherapy are:

  1. It may help shrink size of tumor making it easier to resect.
  2. Helps kill tumor cells that have spread to other organs.
  3. Assess response to chemotherapy. If response is not good an alternative combination of drugs can be offered. A new agent called MTP-PE is also being used in patients with osteosarcoma. This drug is related to the BCG vaccine used to immunize people against tuberculosis. It is thought that it helps eradicate residual tumor cells not killed by chemotherapy agents.

PROGNOSIS
Survival is better in patients that have localized tumors (i.e tumors that did not spread to other regions). Survival rate is about 65% to 85% in patients treated with adjuvant chemotherapy. Factors that contribute to poorer outcome include tumors arising in skull or vertebrae, tumors presenting at multiple location, and tumors occurring in children <10 years of age.

EWING SARCOMA

This is the second most common malignant tumor of the bone. The incidence is 2.1/million in whites and 0.3/million in black.

SYMPTOMS
Usually presents with local pain and swelling of the affected bone. It commonly affects bones of the legs, and hip bones. However Ewing tumor may develop in any bone of the body including the ribs, jaw and skull. There may be associated fever and Ewing tumor may initially be confused with osteomyelitis (bacterial infection of the bone). Some children with this type of tumor have presented with inability to walk.

INVESTIGATIONS
Besides obtaining history and performing complete physical examination, some tests helps in making and/or confirming the diagnosis of Ewing sarcoma. These test include:

  1. X-ray of affected bone.
  2. CT scan or MRI of affected bone. Sometimes both studies are required.
  3. Biopsy of the tumor so as to obtain specimen for pathologic diagnosis. This sample is also subjected to very special test to help differentiate from other tumors that involve the bone.
  4. Bone scan to determine how far the tumor has spread at the primary site and also to determine if other bones are affected.
  5. Bone marrow aspirate and biopsy because this tumor sometimes spread into the bone marrow.
  6. Chest CT scan because in 18% of cases the tumor spreads into the lungs.

TREATMENT MODALITIES
These includes:

  1. Surgery
  2. Chemotherapy
  3. Radiotherapy

Surgery
Surgical removal of the tumor is recommended for affected bone if it is technically possible to remove the entire tumor and some surrounding unaffected bone and if removal of the affected site will not be associated with significant functional impairment. Amputation may be required for tumors located in the long bones of the arms and legs.

Chemotherapy
The use of chemotherapy has improved outcome of treatment of patients with Ewing sarcoma especially if the tumor has spread to other areas of the body. Chemotherapy is given for up to 18 months. One to two cycles of chemotherapy may be given prior to surgical removal of the tumor.

Radiotherapy
Unlike osteosarcoma, Ewing sarcoma is sensitive to radiation. Radiation therapy is given to the primary site, i.e the site where the tumor is. This helps in killing tumor cells that may have spread to surrounding tissues.

Prognosis
With the current available treatments , which include chemotherapy, radiotherapy and surgery , about 55 - 60% of patient with Ewing sarcoma are alive after 5 years. Children with Ewing sarcoma affecting bones of the leg have a better outcome than those with tumor affecting bones of the arms, hips, skull and trunk. The survival of children with recurrent tumor is poor. These children are treated with high doses of chemotherapy followed by bone marrow transplant. The bone marrow is obtained from the patient (autologous bone marrow transplant).