Osteosarcoma

By Prithvi Basak

Osteosarcoma or osteogenic sarcoma is a cancerous medical condition characterized by the presence of a tumor of bone. It occurs due to the conversion of healthy bone-forming cells into cancerous tumors. It usually affects children or teenagers.

Osteosarcoma is a type of bone cancer that occurs majorly in the age groups of 10 to 14. It begins with the conversion of bone-making mesenchymal cells into tumor cells. These tumor cells make bone tissue that resembles healthy bone tissue but is not strong. The tumor usually infects the rapidly growing bones in children, like long bones of legs and arms. In adults, it usually affects the flat bones like the jaw and pelvis. Affected people experience pain, swelling, or a limp at the site of the tumor. Osteosarcoma occurs in two forms called the primary form and the secondary form.

Moreover, due to the highly heterogeneous nature of manifestation of osteosarcoma, it can be divided into three types based on its position and their further subtypes based on the degree of manifestation. Treatment and diagnosis for osteosarcoma widely depend upon the type and subtype of the tumor. Several genetic reasons have been investigated as causes for osteosarcoma. The environment also plays an important role in triggering bone tumors.

Etiology of Osteosarcoma

A tumor develops when the DNA of a normal bone-forming cell guides it to divide at an abnormal rate. It results in poorly formed bone cells that invade healthy bone tissue and cause trouble. The cancerous or tumor cells may or may not spread to other sites in the body. Various genes can cause a healthy bone cell to become cancerous if it gets altered or damaged. The origin of osteosarcoma depends on several factors like genetics and the environment of the affected person. The genetic aberrations that can lead to osteosarcoma are listed below:

• Hereditary retinoblastoma- Mutation in gene RB1 can increase the risk of osteosarcoma along with bilateral retinoblastoma.

• Bloom syndrome- Mutation in the gene named BLM can imbalance the stability of DNA during replication. As a result, it can lead to osteosarcoma along with short stature and UV-induced rashes.

• Werner syndrome- A fault in the gene WRN can lead to adult progeria, which further increases osteosarcoma in later stages.

• Rothmund-Thompson syndrome- Mutation in RECQL4 gene causes predisposition of osteosarcoma along with chronic gastrointestinal defects.

Other reasons for osteosarcoma can be electrical burns, exposure to beryllium, orthopedic prosthetics, bone infarction, and bone infection. In addition, Paget’s disease is a bone disorder that can also lead to osteosarcoma.

Effects and Types of Osteosarcoma

The symptoms or effects of osteosarcoma are bone pain during physical activity. The pain can cause a limp at the site of the tumor. In addition, swelling can occur at the affected bone site. Fever, along with reduced joint movement and night sweats, are other signs. The signs and symptoms vary with the type of osteosarcoma.

Osteosarcoma can be classified as primary or secondary based on its site of occurrence. These are described below:

• The primary form of osteosarcoma manifests in the long bones of legs or arms. Knee bones are another common site for primary form bone tumors.

• The secondary form of osteosarcoma affects the flat bones and is found in adults majorly. The potential sites include the jawbones or the pelvis.

Based on position and degree of manifestation by the tumor, osteosarcoma is further divided as follows:

• High-grade osteosarcomas- The tumor cells in this category divide at the fastest rate and do not resemble normal bone tissue. These tumor cells are mostly found in children of growing age. These are further classified as:

• Osteoblastic

• Chondroblastic

• Fibroblastic

• Small cell

• Telangiectatic

• Low-grade osteosarcomas- The tumor cells in this type of osteosarcoma as the slowest growing. Moreover, the cells resemble normal bone and show few dividing cells. these are further classified as:

• Parosteal

• Intramedullary

• Intermediate grade osteosarcomas- These types of osteosarcoma are between the high-grade and low-grade tumors. The periosteal type is its subtype.

Diagnosis and Treatment for Osteosarcoma

Medical history or physical exam can determine the possible prognosis of osteosarcoma. Hereditary or genetic studies confirm genetic causes of the tumor, or the usual checkup involves checking of lumps or swelling around bones. Various imaging tests like X-rays, CT-scan, MRI, PET scans, or bone scans can confirm the presence of tumor mass. They can also predict unusual changes in the bones due to osteosarcoma. A biopsy is required if the primary tests confirm osteosarcoma. A small sample of bone tissue is collected from the swelled area. A needle is used to make a surgical incision in the skin.

Treatment for osteosarcoma depends on the underlying cause and degree as well the prognosis of the tumor cells. The primary focus of treatment is to stop the spread of tumor cells in other surrounding tissues or bones. Chemotherapy or surgery are the two options to treat osteosarcoma. Intravenous medication to kill the tumor cells is prescribed in case of chemotherapy. Radiation therapy can also be performed to kill osteosarcoma. The surgical therapies are done in severe cases, and these include:

• Limb-sparing surgery

• Amputation of leg or arm

• Rotationplasty

By Prithvi Basak