A 55-year-old man found to have a large right renal mass is noted incidentally to have a hemoglobin of 19 g/dL and hematocrit of 56%. No cause of secondary erythrocytosis such as chronic hypoxia is identified. This paraneoplastic manifestation results from:

• A Cross-reactivity of tumor antigens with red cell receptors
• B Ectopic secretion of parathyroid hormone-related peptide
• C Production of a granulocyte colony-stimulating factor analog
• D Ectopic production of erythropoietin by the tumor ✓

Explanation

Renal cell carcinoma can produce erythropoietin ectopically, causing paraneoplastic polycythemia; hepatocellular carcinoma and cerebellar hemangioblastoma behave similarly. PTHrP secretion by renal cell carcinoma instead produces hypercalcemia, making option B the strongest distractor since both are recognized paraneoplastic syndromes of this tumor. Granulocyte colony-stimulating factor production causes leukocytosis rather than erythrocytosis. Recognition of polycythemia as a presenting clue to occult renal cell carcinoma is a classic examination point.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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