Cancer · UKMLA & AKT
Hypercalcaemia of malignancy
A free high-yield preview for the UKMLA Applied Knowledge Test, covering how to recognise this condition. The full SA Note notes add investigations, management and complications, with practice questions on this topic.
Key high-yield points
- PTHrP-mediated (humoral) - 80% of cases: tumour cells secrete PTHrP, which binds PTH/PTHrP receptor → increased osteoclast activity + renal calcium reabsorption; elevated calcium suppresses endogenous PTH → PTHrP elevated, PTH suppressed, phosphate low
- Cancers: squamous cell lung cancer, renal cell carcinoma, breast cancer, endometrial cancer
- Osteolytic bone metastases: direct tumour invasion stimulates local osteoclast activity via cytokines (RANKL); PTH suppressed; breast cancer and multiple myeloma
- Autonomous vitamin D production: lymphoma macrophages convert 25-OH vitamin D → 1,25-dihydroxyvitamin D (calcitriol) via 1-alpha-hydroxylase → excess intestinal calcium absorption; same mechanism as sarcoidosis
Key discriminator: in PTHrP-mediated hypercalcaemia PTH is suppressed and PTHrP is elevated. In primary hyperparathyroidism PTH is elevated - biochemistry is how you tell them apart.
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