Bone cancer

Introduction

Bone cancer can begin in any bone in the body, but it most commonly affects the pelvis or the long bones in the arms and legs. Bone cancer is rare, making up less than 1 per cent of all cancers. In fact, noncancerous bone tumours are much more common than cancerous ones. Bone cancer develops in the skeletal system and destroys tissue. It can spread to distant organs, such as the lungs. Most of the time when an adult with cancer is told they have cancer in the bones, the doctor is talking about cancer that started somewhere else and then spread to the bones. This is called bone metastasis. Bone cancer can begin in any bone in the body, but it most commonly affects the pelvis or the long bones in the arms and legs. 

The 5-year survival rate is the percentage of people with bone cancer who are likely to survive to at least 5 years after diagnosis. However, if cancer spreads to distant sites, such as the lungs, the 5-year survival rate reduces to 33%. 

 An estimated 3,610 people of all ages (2,100 men and boys and 1,510 women and girls) in the United States will be diagnosed with primary bone sarcoma. In 2020, it was estimated that about 400 of these cases will occur in people age 15 to 19.

Normal bone tissue:

Bone is the supporting framework for your body. The hard, outer layer of bones is made of compact (cortical) bone, which covers the lighter spongy (trabecular) bone inside. The outside of the bone is covered with fibrous tissue called the periosteum. Some bones have a space inside called the medullary cavity, which contains the soft, spongy tissue called bone marrow (discussed below). The tissue lining the medullary cavity is called the endosteum.

Most bones start out as a softer, more flexible form of tissue called cartilage. Cells in the body then lay calcium down onto the cartilage to form bone. After the bone is formed, cartilage may remain at the ends to act as a cushion between bones. This cartilage, along with ligaments and other tissues connect bones to form a joint. In adults, cartilage is mainly found at the end of some bones that are part of a joint. Cartilage can also be found in other parts of the body, such as on the ends of the ribs, in parts of the nose and ears, and in the trachea (windpipe) and larynx (voice box). The bone itself contains 2 kinds of cells- 

  • Osteoblasts are cells that lay down new bone.
  • Osteoclasts are cells that dissolve old bone.

New bone is always forming while old bone is dissolving. This helps keep the bones strong. In some bones, the marrow is only fatty tissue. In other bones, it contains blood-forming cells. These cells make new red blood cells, white blood cells, and blood platelets. There are other cells in the bone marrow, too, such as plasma cells and fibroblasts. Any of these bone cells can develop into cancer.

Causes and risk factors 

Scientists have learned how certain changes in the DNA in bone cells can cause them to become cancerous. These changes sometimes result from factors such as exposure to radiation. But the gene changes leading to bone cancer are usually acquired during life rather than inherited from a parent. Genes that normally help cells grow, divide, or stay alive can sometimes change to become oncogenes. These mutations are present only in the cancer cells, so they cannot be passed on to the person’s children. While scientists need to carry out more research into the precise cause of bone cancer. Risk factors for developing bone cancer include:

  • being under 20 years of age
  • exposure to radiation, such as receiving radiation therapy for a different cancer
  • a previous bone marrow transplant
  • having a close relative with bone cancer
  • individuals with hereditary retinoblastoma, a type of eye cancer that most commonly develops in children
  •  people with long term inflammatory diseases, such as Paget’s disease, might  be at a slightly higher risk  of developing bone cancer later in life.

Diagnosis

At this time, there are no widely recommended screening tests for bone cancer in people who aren’t known to be at increased risk. Still, most bone cancers are found at an early stage, before they have clearly spread to other parts of the body. Symptoms such as bone pain or swelling often prompt a visit to a doctor.

A doctor may order a blood test to rule out other possible causes. They will then refer the person to a bone specialist. Imaging tests can help determine the location and size of bone tumours, and whether the tumours have spread to other parts of the body. The types of imaging tests recommended depending on your individual signs and symptoms. Tests may include:

  • Bone scan
  • Computerized tomography (CT)
  • Magnetic resonance imaging (MRI)
  • Positron emission tomography (PET)
  • X-ray

Biopsy

To grade and stage a tumour, as well as assessing whether it is benign or malignant, a doctor may request a biopsy. Testing can tell your doctor whether the tissue is cancerous and, if so, what type of cancer you have. It can also reveal whether the tumour cells are growing quickly or slowly.                                                             

Several different types are available for people with bone cancer, including:          

  • Inserting a needle through your skin and into a tumor. During a needle biopsy, your doctor inserts a thin needle through your skin and guides it into the tumor. Your doctor uses the needle to remove small pieces of tissue from the tumor.
  • Surgery to remove a tissue sample for testing. During a surgical biopsy, your doctor makes an incision through your skin and removes either the entire tumor or a portion of it.

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