Immunochemical characterization of circulating parathyroid hormone-related protein in patients with humoral hypercalcemia of cancer

Article Abstract:

Some cancer patients develop hypercalcemia, or elevated levels of calcium in their blood. Hypercalcemia is generally associated with a poor prognosis. The condition was known to result because the tumors produced a protein that is similar to parathyroid hormone and binds to parathyroid hormone receptors on normal cells. This protein, the parathyroid hormone-related protein (PTHRP), has been isolated and its gene cloned and sequenced. These developments have permitted the development of specific assays for PTHRP; little or no PTHRP is present in normal subjects, whereas the substance is elevated in patients with hypercalcemia due to cancer. The substance was normal in patients with other types of hypercalcemia. PTHRP is, however, elevated in both breast tissue and breast milk. Assays have been developed to detect specific portions of the PTHRP molecule. In particular, one detects the presence of the first 74 amino acids in the chain, and another detects the amino acids from position 109 to 138. In patients with chronic renal failure, levels of the first 74-amino acid chain were normal, but levels of the 109 to 138 chain were elevated, suggesting that the molecule may be split into pieces. This has been confirmed by using antibodies to remove the first piece from blood plasma. The second piece remained in the plasma, indicating that they must be separate. These assays may be especially valuable in the differential diagnosis of hypercalcemia due to cancer as opposed to other causes. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Parathyroid hormone-related peptide in sickness and in health

Article Abstract:

For 50 years, some have suspected that parathyroid hormone or a related substance might be involved in the development of hypercalcemia (elevated levels of calcium in the blood) in some cancer patients. Recently it has become clear that some tumors do secrete a substance which is similar to parathyroid hormone. Now, in the April 19, 1990 issue of The New England Journal of Medicine, researchers present comprehensive data on this substance, parathyroid hormone-related protein, or PTHRP. PTHRP is found in the blood of hypercalcemic patients with cancer, but not in patients with hypercalcemia due to other causes such as hyperparathyroidism. Further research will be necessary to determine if this protein is present in a minority of patients with hypercalcemia due to other causes to learn its true diagnostic value. It also seems that the protein is present in some cancer patients with normal levels of serum calcium; the meaning of this observation remains uncertain. PTHRP apparently also has some normal function, as it is found in high concentrations in breast tissue and milk. Although circulating PTHRP is not found in lactating women, milk contains a 10,000-fold higher concentration of PTHRP than normal serum. The substance may affect calcium metabolism in the breast or perhaps improve its absorption by the infant. The identification of this factor will almost certainly provide new insights into the physiological regulation of the critical ion calcium. (Consumer Summary produced by Reliance Medical Information, Inc.)

Calcium in the body, Calcium (Nutrient), editorial

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Hypercalcemia associated with cancer

Article Abstract:

Hypercalcemia is reported to occur in up to 20 to 30 percent of patients with cancer at some time during the course of their disease. In patients with local osteolytic hypercalcemia, the hypercalcemia results from the marked increase in osteolytic bone resorption in areas surrounding the malignant cells within the marrow space.

United Kingdom, Science & research, Risk factors, Cancer patients

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