Osteosarcoma in Children
What is osteosarcoma?
Osteosarcoma, also called osteogenic sarcoma, is the most common primary malignant bone tumor in children, adolescents, and young adults. Osteosarcoma only ranks behind lymphomas and brain tumors as the most prevalent pediatric solid tumor. Its hallmark is the presence of immature bone or osteoid formed by malignant cells. This means that it is a bone-producing sarcoma—that the malignant cells produce immature woven bone, or osteoid—hence the name “osteosarcoma.”
Osteosarcoma in Children
Osteosarcoma most frequently occurs in children and young adults between the ages of 10 and 30. It usually starts with pain and swelling in a bone, most commonly around the knee, followed by shoulder, hip and other sites. Though the exact cause of osteosarcoma is mostly unknown, patients who have specific genetic mutations found in rare genetic disorders, such as TP53 mutations in the Li-Fraumeni syndrome or RECQL4 mutations in the Rothmund-Thomson syndrome, or exposure to ionizing radiation, have a higher chance of developing osteosarcoma. The pain may vary from a dull ache to severe unrelenting pain. It is not unusual for osteosarcoma to be mistaken for an injury or infection of the bone, both of them being much more common entities. As a result, the diagnosis of osteosarcoma is sometimes delayed, which makes treatment and cure difficult. As a rule, any lump or swelling in the limbs of a child should not be ignored, if it is > 5 cm, deep, painful or increasing in size.
Laboratory tests may be used to aid in diagnosis. For example, a high level of alkaline phosphatase in the blood may be used to follow up response of osteosarcoma to treatment. Additionally, radiographs, computed tomography, and magnetic resonance imaging are often used in diagnosis and for detection of metastases.
The standard of care for osteosarcoma involves a diagnosis by an initial biopsy (mostly a core needle biopsy), followed by pre-operative chemotherapy for 2-3 months. Surgery is then performed to remove the tumor. After that, post-operative chemotherapy based on the initial response to preoperative chemotherapy is administered. Typically, patients who have a good response receive the same chemotherapy post-operatively, while poor responders may receive an intensified or alternative chemotherapy regimen in an attempt to counter the chemo-resistance of the tumor.
Advances in limb salvage surgery for osteosarcoma in young children
Fortunately, childhood bone cancer is curable, if detected in time, with cures rates reaching 70- 80 percent in localised disease. Not just that, the legs or hands of these patients can be saved with good form and function in more than 90 percent of patients. This is performed through "limb salvage surgery", where the cancerous bone is completely removed and the defect in the bone is suitably reconstructed, thereby restoring the normal form and function of the limb. This has been made possible by development of effective chemotherapy, modern prosthesis/ implants for limb reconstruction, and improved surgical techniques. Multimodality tumor board having representation from orthopedic oncology, pediatric oncology, musculoskeletal radiology and pathology forms a very important part of treatment of these patients.
Limb saving surgeries in growing children are particularly challenging ; this is largely a result of the small size of remaining bone and growth disturbance of operated limb as compared to the corresponding bone on other side. For these reasons, it is very useful to preserve as much of the normal bone as possible in children, as one attempts to save not just the limbs but also the growth plates at the ends of bones. Computer navigation, a new technology for high precision bone cancer surgery, has proved to be a boon in this direction. Use of computer navigation has enabled orthopedic oncologists to save limbs from cancer, while they continue to grow.
The use of expandable prosthesis (metallic prosthesis which can grow as the child grows) is also an important technological advancement for pediatric bone cancer treatment. This prothesis is used in young growing children, where there is significant growth remaining, and the growth plates cannot be saved. They ensure that the length of the cancer affected limb is not different from that of the normal limb, by the time the growth of the child ends.
Another effective technique that has we now use for children with bone cancer is the use of cancer bearing bone itself for restoring the continuity of the bone. Here, the cancerous bone is removed as usual, and then it is made cancer free by using intraoperative radiotherapy or cryosurgery. Once the cancer free bone is retrieved, it is placed back in to the defect from where it was removed, and fixed with plates. This is a very safe and durable reconstruction method, which allows the child to perform all activities that he does with a normal limb.
Last but not the least, rotationplasty is another form of saving a highly functional limb after complete cancer removal. The whole of the affected segment of the limb is removed barring the nerves and vessels supplying the lower part of the limb. This part is then rotated 180 degrees and fixed to the upper part of the remaining leg. This makes the ankle joint act as the new knee joint, so the the child can now use an external prosthesis for walking. Again, this surgery is for young growing children, and it enables the child to perform all sorts of activities.