Cancer · UKMLA & AKT
Hypercalcaemia of malignancy
A free high-yield preview for the UKMLA Applied Knowledge Test. Below are the key points to recognise hypercalcaemia of malignancy — the full SA Note notes add investigations, management, complications and 10 practice questions.
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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