Bone is living, connective tissue that has multiple functions such as protecting internal organs, storing minerals, and supporting body weight. In adults, bone is also the primary site of hemopoiesis , the formation of blood cells.

Bone consists mostly of calcium phosphate and collagen, a mineral and protein that make bones strong, yet flexible and able to withstand stress. There are three types of bone cells in mature bone tissue: osteoblasts, osteocytes, and osteoclasts. Osteoblasts and osteocytes, found in the surface of the bone, are involved in bone deposition , the process in which bone tissue regenerates itself. Osteoclasts, on the other hand, are embedded deep in the bone and are involved in the resorption , or break down, of bone tissue. The delicate balance between bone deposition and resorption is what maintains bone mass, density and structure.

During adolescence, bone mass development accelerates dramatically as the rate of bone deposition exceeds the rate of resorption. This results in bones that are larger, denser, and heavier. After peak bone mass is achieved, usually around the age of 30, bones begin to break down faster than they rebuild themselves. Men and women lose bone at the same rate, until menopause, when hormonal changes (decreasing estrogen) speed up bone loss in women, putting them at increased risk for bone disease. Calcium and Bones

Calcium is the most abundant mineral in the body and 99 percent of it is stored in the skeletal structure. Calcium not only gives bones strength and structure, but also plays an important role in several body functions such as muscle contractions and kidney functioning. If a person's diet does not contain sufficient levels of calcium (1,000 mg a day for men, 1200 mg for women, and 1500 mg for postmenopausal women), the body will withdraw calcium from the bones to meet its needs. The resulting decrease in bone tissue can lead to bone disease.

• Bone mass Loss - Bone loss and bone weakening is a common symptom in patients who have some form of bone cancer. However, there are many forms of bone cancer which can cause different symptoms, depending on the size and location of the cancer. Some types of bone cancers can interfere with normal movements and can weaken the bones, occasionally leading to fractures. In bone containing metastasized cancer cells, the bone derived growth factor transforming growth factor, stimulates the cancer cells to produce cytokines and other growth factors that in turn trigger osteoclasts, cells that break down bone tissue. This upset to the delicate balance of bone resorption and formation can lead to vertebral collapse, spinal cord compression, and osteoporosis.
  
• Primary Bone Cancer - Bone cancer is a growth found in any part of the bone. Most bone cancers are called sarcomas , which are cancers that develop predominantly from bone, cartilage, muscle, fibrous tissue, fatty tissue, or nerve tissue. Bone cancer originating in the bone itself is known as primary bone cancer, and may be malignant (cancerous) or benign. Both types may grow and compress healthy bone tissue, however, benign tumors do not spread and are rarely life-threatening. Primary bone cancer is also very rare, with approximately 2,500 new cases diagnosed each year in the United States. More commonly, bones are the site of cancers that result from the spread of cancer cells (bone metastases) from another organ via the blood or lymphatic system to the bones.

  Bone pain is the most common symptom of bone cancer, often the result of weakening bones or a tumor that invades bone or presses against nerves or other tissues. Swelling and tenderness in or near joints is also common. Frequent fractures may be an indication of cancer, as bones weakened by tumors are more susceptible to injury. Symptoms may also include fatigue, fever, weight loss, and anemia (loss of oxygen-carrying red blood cells). All of these symptoms can mimic those of other less serious conditions, so it is important to confirm them with your doctor.

• Bone Metastases - Metastatic cancer is a cancer that has spread from the original site (breast, lungs, etc.) to another part of the body. Cancerous cells can break away from the original tumor and travel throughout the body via the blood or lymphatic system (although most often cancerous cells travel through the bloodstream). When this happens, the cancerous cells can attach to a new area of the body and begin to grow, forming new tumors in this new location. Bones are one of the most common areas of the body for these traveling cancerous cells to land. This cancer of the bone is called bone metastases , since the original site of the cancer was in another location of the body. The most common types of cancer that can lead to bone metastases include cancer of the lungs, kidney, breast, ovary, prostate, and colon.

  Pain in the bones is the main symptom of bone metastases. The pain may be worse at night at first, and may come and go. Later on the pain may become constant and may worsen when the patient is active. Some patients with bone metastases experience relatively mild symptoms, such as decreased appetite and unusual sleep patterns due to discomfort. Others may notice frail or brittle bones, nausea, fatigue, muscle weakness, restlessness, and confusion.

An unfortunate side effect of some cancer treatments is that although they may help with treating the cancer, they may also cause bone loss. For example, chemotherapy has been shown to cause premature bone loss by inducing ovarian failure, which prevents the ovaries from releasing estrogen into the bloodstream. Before beginning any cancer treatment, talk with your doctor about possible effects including bone loss.

Reviewed by Jon Hinrichs, M.D.