Parathyroid hormone-related protein, bone metastases and hypercalcaemia of malignancy.

Breast cancer patients frequently develop bone metastases. A newly discovered peptide, Parathyroid Hormone Related Protein (PTHrP), causes humoral hypercalcaemia of malignancy. We have studied whether production of this protein by breast cancers leads to the development of bone metastases or hypercalcaemia. PTHrP was produced by nearly 60% of early breast cancers and its production by the tumours was associated with malignant mammographic microcalcification, and the development of both bone metastases and hypercalcaemia. The hypercalcaemia associated with bone metastases has been shown to have a significant humoral component and measurement of plasma PTHrP in patients with hypercalcaemia is diagnostically useful. Potential mechanisms of preventing bone metastasis are discussed.