Lymphoma Calcitriol Hypercalcaemia — RACP Adult Medicine MCQ

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HardEndocrinology & DiabetesLymphoma Calcitriol HypercalcaemiaRACP Adult Medicine

A 58-year-old woman with metastatic breast cancer develops hypercalcaemia (corrected calcium 3.5 mmol/L) with a suppressed PTH and normal PTHrP. Her 1,25-dihydroxyvitamin D is elevated. She has widespread lymphadenopathy. What additional diagnosis should be considered?

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Correct answer: B — Lymphoma with ectopic calcitriol production

When hypercalcaemia occurs with suppressed PTH, normal PTHrP, and elevated 1,25-dihydroxyvitamin D (calcitriol), the differential includes granulomatous diseases (sarcoidosis) and lymphoma. Lymphomas (particularly Hodgkin and some non-Hodgkin lymphomas) can produce 1,25-dihydroxyvitamin D via tumour-associated macrophage 1-alpha-hydroxylase activity, identical to the mechanism in sarcoidosis. This patient with breast cancer and widespread lymphadenopathy may have concurrent lymphoma (or granulomatous inflammation in lymph nodes). Biopsy of the lymphadenopathy is essential. Treatment includes corticosteroids (which suppress 1-alpha-hydroxylase) plus hydration and bisphosphonates.

Reference: eTG – 2025 – Endocrinology; eTG – 2025 – Haematology