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PTHrP Hypercalcaemia — SCE Medical Oncology MCQ

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HardBreast CancerPTHrP HypercalcaemiaSCE Medical Oncology

A 62-year-old woman with metastatic breast cancer develops hypercalcaemia. Her PTHrP (parathyroid hormone-related peptide) is markedly elevated. PTH is suppressed. What is the mechanism of her hypercalcaemia?

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Correct answer: E — PTHrP-driven renal calcium retention and osteoclastic bone resorption

Tumour-derived PTHrP increases renal calcium conservation and osteoclastic bone resorption while suppressing native PTH. PTHrP-driven calcitriol synthesis and increased intestinal calcium absorption: PTHrP principally mimics PTH at bone and kidney rather than generating calcitriol excess. PTHrP-driven renal phosphate retention and reduced osteoclast activity: PTHrP promotes phosphaturia and osteoclastic resorption rather than phosphate retention. PTHrP-driven parathyroid hyperplasia and increased intact-PTH secretion: intact PTH is suppressed in humoral hypercalcaemia of malignancy. PTHrP-driven tumour lysis and release of intracellular calcium stores: tumour lysis does not mediate sustained PTHrP hypercalcaemia.

Reference: Renal and skeletal actions of parathyroid-hormone-related peptide (Published November 1992): https://pubmed.ncbi.nlm.nih.gov/1338636/; NICE NG81 advanced breast cancer: recommendations (Current NICE recommendations, accessed July 2026): https://www.nice.org.uk/guidance/ng81/chapter/Recommendations