Alkaline phosphatase, or ALP, is a commonly measured enzyme found in several body tissues, including bone. Bone cancers and other tumors can result in elevated blood levels of ALP, but are not the only possible causes. The properties of ALP allow its use for both initial diagnosis and monitoring the course of bone cancers following treatment.
Bone Tumors
Your bones contain a complex mix of cell types, including those that make bone, cartilage, fibrous tissue, fat and blood cells. Any of these cells can be the origin of abnormal growths or tumors, including bone cancer. Primary bone tumors arise in the bones themselves, and can be benign or cancerous. Common examples of bone cancers include osteosarcomas, arising from the bone-forming cells called osteoblasts; chondrosarcomas from cartilage; and fibrosarcomas from fibrous tissue. Secondary bone cancers are those that have spread, or metastasized, to the bones from a cancer elsewhere in the body. Cancers from the prostate, breast, kidney, thyroid and lung are the most common example of these, according to MedlinePlus.
Total Alkaline Phosphatase
Alkaline phosphatase is a cellular enzyme found in highest concentrations in bone, liver, biliary tract, the intestines and placenta. Each of these tissues produces a slightly different form of ALP, called an isoenzyme, which are usually measured in aggregate and reported as total alkaline phosphatase. Total ALP levels vary somewhat with age and gender, but are highest during your childhood and teen years while active bone growth is occurring. Normal adult levels average 40 to 125 U/L, according to the Mayo Medical Laboratories, but can become elevated due to liver and biliary conditions, pregnancy, certain colon disorders and any bone disease that involves new bone formation, including many bone cancers.
Alkaline Phosphatase in Bone Disease
Bone cancers may initially be symptom free or present with fractures, bone pain or a mass. If your health-care provider is concerned about the possibility of a bone tumor, the initial evaluation will usually include bone X-rays and blood tests including an alkaline phosphatase level. Any tumor or other bone disorder that results in increased osteoblastic, or bone-forming, activity will increase the circulating levels of ALP. ALP isoenzyme levels might also be measured to confirm that any elevation is due to the bone form of the enzyme. The isoenzyme from bone should be particularly elevated when bone cancer, other bone tumors, Paget's disease, osteomalacia or hyperparathyroidism is present.
Treatment and Follow-Up
Primary bone cancers can result in very high levels of ALP, with secondary bone cancers generally showing less marked elevations depending on the tumor type and extent of bone involvement. Treatment can involve any combination of surgery, chemotherapy and radiation, again depending on the location and type of cancer. ALP levels should return to normal after successful treatment of a cancer, but can remain elevated or increase if a tumor persists, according to Lab Tests Online. Measuring ALP at regular intervals after treatment can therefore be a convenient long-term monitoring tool.
