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About bones
The human skeletal system is made up of more than 200 bones that
protect the internal organs, allow people to stand upright, and attach
to muscles that allow movement. Bones are connected to other bones by
ligaments, which are bands of tough, fibrous tissue, while cartilage
covers and protects the joints where bones come together. Bones are
hollow and filled with bone marrow, which is the spongy, red tissue that
produces blood cells. The cortex is the hard, outer portion of the
bone.
Bone is a tissue that consists of collagen (a soft, fibrous tissue)
and calcium phosphate (a mineral that helps harden and strengthen the
bone). There are three types of bone cells:
- Osteoclasts break down and remove old bone.
- Osteoblasts build new bone.
- Osteocytes carry nutrients to the bone.
About bone cancer
Cancer can occur in any part of the bone. Cancer begins when normal
cells in the bone change and grow uncontrollably, forming a mass called a
tumor. A bone tumor can be benign (noncancerous) or malignant
(cancerous, meaning it can spread to other parts of the body). Even
though a benign tumor does not spread outside the bone, it can grow
large enough to press on surrounding tissue and weaken the bone. A
malignant tumor can destroy the cortex and spread to nearby tissue. If
bone tumor cells get into the bloodstream, they can spread to other
parts of the body, especially the lungs.
There are different types of bone cancer, including:
- Osteosarcoma and Ewing sarcoma are two of the most common types of bone cancer and mostly occur in children and young adults.
- Chondrosarcoma is cancer of the cartilage and is more common in adults.
- Chordoma is a type of bone cancer that typically starts in the lower spinal cord.
Rarely, soft tissue sarcomas begin in the bone, including:
- Malignant fibrous histiocytoma (MFH), which makes up less than 1% of bone tumors and is usually found in adults. An arm or leg, especially around the knee joint, is the most common place for MFH to appear.
- Fibrosarcoma is also more common among adults, particularly during middle age, and most often begins in the thighbone.
- Paget’s disease of the bone generally occurs in older adults and involves the overgrowth of bony tissue.
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