Parathyroid hormone-related protein (or PTHrP) is a protein occasionally secreted by cancer cells (breast cancer, certain types of lung cancer). PTHrP is related in function to the "normal" parathyroid hormone. When a tumor secretes PTHrP, this can lead to hypercalcemia. As this is sometimes the first sign of the malignancy, hypercalcemia caused by PTHrP is considered a paraneoplastic phenomenon.

The protein was first isolated in 1988 by Broadus et al. Miao et al showed that disruption of the PTHrP gene in mice caused a lethal phenotype and distinct bone abnormalities, suggesting that PTHrP has a physiological function.

PTHrP shares the same N-terminal end as parathyroid hormone and it therefore can bind to the same receptor (the Type I PTH receptor).

PTHrP aids in normal mammary gland development and lactation as well as placental transfer of calcium.

References

• Broadus AE, Mangin M, Ikeda K, Insogna KL, Weir EC, Burtis WJ, Stewart AF. Humoral hypercalcemia of cancer. Identification of a novel parathyroid hormone-like peptide. N Engl J Med 1988;319:556-63. PMID 3043221.
• Miao D, Li J, Xue Y, Su H, Karaplis AC, Goltzman D. Parathyroid hormone-related peptide is required for increased trabecular bone volume in parathyroid hormone-null mice. Endocrinology 2004;145:3554-62. PMID 15090463.

Oncology