Hypercalcemia is an abnormally high level of calcium in the blood, usually more than 10.5 milligrams per deciliter of blood. It is the most common life-threatening metabolic disorder associated with cancer.
Calcium plays an important role in the development and maintenance of bones in the body. It is also needed in tooth formation and is important in other body functions. As much as 99% of the body's calcium is stored in bone tissue. A healthy person experiences a constant turnover of calcium as bone tissue is built and reshaped. The remaining 1% of the body's calcium circulates in the blood and other body fluids. Calcium in the blood plays an important role in the control of many body functions, including blood clotting, transmission of nerve impulses, muscle contraction, and other metabolic activities.
Cancer-caused hypercalcemia produces a disruption in the body's ability to maintain a normal level of calcium. This abnormally high level of calcium in the blood develops because of increased bone breakdown and release of calcium from the bone. The disorder occurs in approximately 10-20% of all cancer cases. The most common cancers associated with hypercalcemia are breast, prostate, and lung cancer, as well as multiple myeloma or other tumors with extensive metastasis to the bone. It may also occur in patients with head and neck cancer, cancer of unknown primary, lymphoma, leukemia, kidney cancer, and gastrointestinal cancer. Hypercalcemia most commonly develops as a late complication of cancer, and its appearance constitutes an emergency.
Several clinical symptoms are associated with cancer-related hypercalcemia. Symptoms may appear gradually and often look like signs of other cancers and diseases. The symptoms of hypercalcemia are not only related to the elevated level of calcium in the blood, but—more importantly—to how rapidly the hypercalcemia develops. The severity of the symptoms is often dependent upon factors such as previous cancer treatment, reactions to medications, or other illnesses a patient may have. Most patients do not experience all of the symptoms of hypercalcemia, and some may not have any signs at all. Rapid diagnosis of hypercalcemia may be complicated because the symptoms are often nonspecific and are easily ascribed to other factors. These symptoms include: