Normal calcium regulation
Kidney function

Hypercalcemia occurs in 10%-20% of people with cancer, although it occurs much less often in children. The cancers most often associated with hypercalcemia are cancer of the breast and lung, as well as certain cancers of the blood, particularly multiple myeloma. Early diagnosis and treatment with fluids and drugs that lower calcium levels in the blood can improve symptoms in a few days, but diagnosis may be difficult. Symptoms of hypercalcemia can appear gradually and may resemble symptoms of many cancers and other diseases. Early diagnosis and treatment are not only lifesaving in the short term, but may also increase the patient's ability to complete cancer therapy and improve the patient's quality of life.

Patients who have advanced terminal cancer and are no longer receiving treatment for the cancer may choose not to be treated for hypercalcemia. This option should be considered by a patient and his or her family in advance, before symptoms of hypercalcemia occur.

Healthy people consume about the same amount of calcium in their diet as their bodies lose in urine, feces, and sweat. Hypercalcemia associated with cancer disrupts the body's ability to maintain a normal level of calcium.

Normal, healthy kidneys are able to filter large amounts of calcium from the blood, excrete the excess not needed by the body, and retain the amount of calcium the body does need. However, hypercalcemia may cause such high levels of calcium in the body that the kidneys are overworked and become unable to excrete the excess. Some tumors produce a substance that can cause the kidneys to excrete too little calcium. This results in a large amount of urine being produced, which then causes dehydration. Dehydration may lead to appetite loss, nausea, and vomiting which make the dehydration worse. Inactivity caused by weakness and tiredness may increase the amount of calcium in the blood by increasing the amount of calcium that is absorbed from the bones. Calcium deposits may collect in the kidneys, causing permanent damage.

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