What Is Bone Cancer?

Bone cancer is an uncommon type of cancer that begins when cells in the bone start to grow out of control.

The information here focuses on primary bone cancers (cancers that start in bones) that most often are seen in adults. Information on Osteosarcoma, Ewing Tumors (Ewing sarcomas), and Bone Metastases is covered separately.

Normal bone tissue

To understand bone cancer, it helps to know a little about 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 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 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).

Bone itself contains 2 kinds of cells.

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

Bone often looks as if it doesn’t change much, but it's actually very active. 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.

Primary bone cancers versus bone metastasis

Cancers that start in the bones are called primary bone cancers. These types of cancers aren’t very common.

Most of the time when an adult with cancer is told they have cancer in the bones, the doctor is talking about a cancer that started somewhere else and then spread to the bones. This is called bone metastasis. It can happen with many different types of advanced cancer, like breast cancer, prostate cancer, and lung cancer. When the cancer cells in the bone are looked at under a microscope, they look like the cancer cells in the organ they came from.

So, if someone has lung cancer that has spread to bone, the cancer cells in the bone look and act like lung cancer cells, not bone cancer cells, so they need treatments that are used for lung cancer.

To learn more about cancer that has spread to the bones, see Bone Metastasis.

Types of primary bone cancers

Primary bone cancers (cancers that start in the bone itself) are also known as bone sarcomas. (Sarcomas are cancers that start in bone, muscle, fibrous tissue, blood vessels, fat tissue, as well as some other tissues. They can develop anywhere in the body.)

There are many kinds of primary bone cancer. Some are rare.

Osteosarcoma

Osteosarcoma (also called osteogenic sarcoma) is the most common primary bone cancer. It starts in an early form of bone cells. It most often occurs in young people between the ages of 10 and 30, but about 1 in 10 osteosarcomas develop in people older than 60. It's rare in middle-aged people, and is more common in males than females. These tumors develop most often in bones of the arms, legs, or pelvis.

This type of cancer is not discussed further on our Bone Cancer pages. For more information on it, see Osteosarcoma.

Ewing tumor (Ewing sarcoma)

Ewing tumors are the second most common type of primary bone cancer in children, teens, and young adults, and the third most common type of bone cancer overall. These tumors are rare in adults older than 30. They occur most often in white people and are rare among African Americans and Asian Americans. 

Most Ewing tumors develop in bones, but they can start in other tissues and organs. The most common sites for this cancer are the hip (pelvic) bones, the bones in the chest wall (such as the ribs or shoulder blades), the bones of the spine, and the long bones of the legs. 

This type of cancer is not discussed further on our Bone Cancer pages. For more information on it, see Ewing Family of Tumors.

Chondrosarcoma

Chondrosarcoma starts in early forms of cartilage cells. It's the second most common primary bone cancer. It's rare in people younger than 20, and the risk of chondrosarcoma goes up as people get older.

Chondrosarcomas can start in any place there's cartilage. Most develop in bones like the pelvic (hip) bones, legs, or arms. Some start in the trachea, larynx, chest wall, shoulder blades, ribs, or skull.

Benign (non-cancerous) tumors such as enchondromas and osteochondromas are more common in the cartilage than are chondrosarcomas. These benign tumors rarely turn into cancer. People who have many of these tumors have a slightly higher chance of developing cancer, but this isn't common.

Chondrosarcomas are given a grade from 1 (I) to 3 (III), which is a measure of how fast they are likely to grow. The lower the grade, the slower the cancer tends to grow and the less likely it is to spread:

• Low-grade (grade I) chondrosarcomas, also called atypical cartilaginous tumors, tend to grow the slowest and are very unlikely to spread.
• Intermediate-grade (grade II) chondrosarcomas are slightly more likely to spread.
• High-grade (grade III) chondrosarcomas are the most likely to spread.

Most chondrosarcomas are grade I or grade II.

Uncommon subtypes of chondrosarcoma

A small number of chondrosarcomas have distinctive features that can be seen with a microscope. These uncommon subtypes often have a different prognosis (outlook):

• Dedifferentiated chondrosarcomas start out as typical chondrosarcomas, but then some parts of the tumor change into cells like those of a high-grade sarcoma (such as an osteosarcoma, fibrosarcoma, or high-grade undifferentiated pleomorphic sarcoma). This type of chondrosarcoma tends to develop in older adults and grows faster than most other chondrosarcomas.
• Mesenchymal chondrosarcomas tend to develop in younger adults. They often grow quickly, and they are more likely to come back after treatment.
• Clear cell chondrosarcomas are rare and tend to grow slowly. They seldom spread to other parts of the body unless they have already come back several times in the original location.

High-grade undifferentiated pleomorphic sarcoma (UPS) of bone

This cancer was previously known as malignant fibrous histiocytoma (MFH) of bone. Undifferentiated pleomorphic sarcoma (UPS) most often starts in soft tissues (connective tissues such as ligaments, tendons, fat, and muscle). It's rare in bones, but when it does occur, it usually affects the legs (often around the knees) or arms. This cancer most often occurs in elderly and middle-aged adults. It's rare in children. It tends to grow locally, but sometimes it can spread to distant parts of the body, like the lungs.

Fibrosarcoma of bone

Fibrosarcoma is another type of cancer that develops more often in soft tissues than it does in bones. It usually occurs in middle-aged adults. Bones in the legs, arms, and jaw are most often affected.

Giant cell tumor of bone

This type of primary bone tumor can be either benign (not cancer) or malignant. The benign form is more common. These tumors are most common in people in their 20s and 30s.

Giant cell bone tumors typically affect the legs (usually near the knees) or arms. They don’t often spread to distant parts of the body, but after surgery they can come back (even more than once) in the place where they started. With each recurrence, the tumor becomes a bit more likely to spread to other parts of the body (most often to the lungs). Rarely, a malignant giant cell bone tumor spreads to other parts of the body without first recurring locally.

Chordoma

This uncommon type of bone tumor occurs in the bones of the spine, most often at the bottom of the spine (sacrum) or the base of the skull. It develops most often in adults older than 30. It's about twice as common in men as in women. Rarely it can develop in children, as well.

Chordomas tend to grow slowly and often do not spread to other parts of the body. They often come back in the same area if they are not removed completely. If they do spread, they most often go to the lymph nodes, lungs, or liver.

Primary bone tumors that are not cancer

Some tumors that start in the bones are benign (not cancer). Benign tumors do not spread to other parts of the body and are not usually life threatening. When they need to be treated they often can be cured with surgery. Types of benign bone tumors include:

• Osteoid osteoma 
• Osteoblastoma 
• Osteochondroma
• Enchondroma
• Chondromyxoid fibroma

Benign giant cell tumors of bone can also be included here. 

Benign bone tumors won't be discussed further here.

Other cancers that develop in bones

Some other cancers develop in the bones, but they don't start in the actual bone cells. These cancers start in early forms of blood cells or immune cells in the bone marrow (the soft inner part of some bones). These are not considered to be primary bone cancers, and they are discussed in more detail elsewhere.

Multiple myeloma

In multiple myeloma, many tumors develop in the bones, but it's not a primary bone cancer because it starts in plasma cells (a type of immune cell) in the bone marrow. Sometimes, myeloma can be found as a single tumor (called a plasmacytoma) in a bone, but most often it has spread to other bones, so it's treated as a widespread disease. 

For more on this type of cancer, see Multiple Myeloma.

Leukemias

Leukemias start in the blood-forming cells of the bone marrow, not in the bone itself. There are many types of leukemia. Most of these are cancers of early forms of white blood cells, but they can also start in other types of blood cells.

For more on this type of cancer, see Leukemia.

Non-Hodgkin lymphomas

Non-Hodgkin lymphomas start in early forms of white blood cells called lymphocytes. Most often these cancers develop in lymph nodes or in other parts of the body that contain lymph tissue. But in rare cases, a lymphoma can show up first in the bones.This is known as a primary non-Hodgkin lymphoma of bone (PLB). It can affect one or many bones. 

PLB is treated based on the type of lymphoma it is. (Most PLBs are diffuse large B-cell lymphomas.) The outlook is generally similar to other lymphomas of the same type and stage.

For more information on the treatment of lymphoma, see Non-Hodgkin Lymphoma.