A 58-year-old man being worked up for haematuria is found to have a left renal mass consistent with renal cell carcinoma. Full blood count shows haemoglobin 19 g/dL and haematocrit 55%. What is the underlying mechanism of this paraneoplastic phenomenon?
- A Inappropriate ADH secretion causing haemoconcentration
- B Ectopic secretion of erythropoietin by tumour cells ✓
- C Parathyroid hormone related peptide production stimulating marrow
- D ACTH cosecretion driving cortisol mediated erythropoiesis
Correct answer: B. Ectopic secretion of erythropoietin by tumour cells
Explanation
Renal cell carcinoma is a classic source of ectopic erythropoietin, producing true secondary polycythaemia in roughly 1 to 5 percent of patients. ADH excess causes hyponatraemia, not erythrocytosis, and PTHrP produces hypercalcaemia, while ACTH cosecretion gives Cushingoid features. Polycythaemia may paradoxically coexist with anaemia elsewhere in the disease and resolves after nephrectomy, which supports its value as a marker of tumour activity.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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