Cancer may start in your bones (called primary bone cancer) or it may start in another area of your body and spread to your bones (called a secondary cancer). Primary bone cancers may start in the new tissue of growing bones, in cartilage (connective tissue between bones), or in the nerve tissue within bone marrow. Secondary bone metastases disrupt the process of bone cell reproduction. All types of cancer that occur in bones can cause pain, bone weakness and increases of calcium levels in the blood.
Causes Pain
Pain is the most common symptom in those with cancer that has spread to the bone, affecting approximately 70 percent of those with bone metastases. It is caused by the stretching of the membrane that covers the bones (periosteum) and by nerve stimulation of the layer of cells lining the inner cavity of the bone (endosteum). Bone pain can be fairly constant and can be worse at night or in certain positions (such as standing) that put weight on the affected bone. It may be difficult to differentiate this pain from arthritis or other bodily aches and pains.
Changes Bone Density and Strength
When cancer spreads to your bones, it can weaken them in one of two ways. Osteolytic metastases (tumors that have spread from another area of the body) destroy bone tissues, forming holes in the bone itself. Osteoblastic metastases cause the bone to overproduce new cells, increasing bone density but also making it more susceptible to fractures.
Pathological fractures (fractures caused by inherent problems with the bone as opposed to external factors) can occur when tumors have destroyed enough bone that it can no longer support normal body functions. Roughly 50 percent of patients with metastatic cancer that has spread to the bone will experience bone fractures every year.
Hypercalcemia
Hypercalcemia is a condition in which there is too much calcium in the blood. Normal bones constantly break down and rebuild. When bones break down, they release calcium into the blood stream, helping the body to carry out vital processes like muscle contraction, nerve function, blood clotting and cell division. Cancer in the bone causes an imbalance between the formation and reabsorption of bone calcium, with too much calcium being released into the blood stream. This can cause a number of side effects, including nausea, vomiting, fatigue, mood disturbances, abdominal pain, constipation, anorexia, dry mouth or throat and extreme thirst, muscle weakness, irregular heart beat, frequent urination, confusion and coma.
