A patient with a flank mass and hypercalcemia has elevated hematocrit. Which paraneoplastic mechanism best explains these findings?

A patient with a flank mass and hypercalcemia has elevated hematocrit. Which paraneoplastic mechanism best explains these findings?

• A. Autoimmune hemolytic anemia
• B. Calcitonin overproduction
• C. Paraneoplastic production of PTH-related peptide and erythropoietin
• D. Renin overproduction

Answer: (C)

Tumors can drive paraneoplastic syndromes by secreting humoral factors that mimic normal hormones. In a renal cell carcinoma presenting as a flank mass with hypercalcemia and a high hematocrit, the best explanation is paraneoplastic production of PTH-related peptide and erythropoietin. PTH-related peptide acts similarly to parathyroid hormone, binding the same receptors and promoting bone resorption as well as renal calcium reabsorption. This leads to increased serum calcium, producing the hypercalcemia observed. At the same time, ectopic erythropoietin production by the tumor stimulates the bone marrow to make more red blood cells, resulting in an elevated hematocrit (polycythemia). Renal cell carcinoma is a classic tumor associated with both effects, which is why a flank mass plus these two lab findings fit perfectly. The other options don’t explain both hypercalcemia and increased red cell mass: autoimmune hemolytic processes would cause anemia rather than high hematocrit; calcitonin overproduction would lower calcium; renin overproduction doesn’t account for the calcium and red cell changes seen here.

Tumors can drive paraneoplastic syndromes by secreting humoral factors that mimic normal hormones. In a renal cell carcinoma presenting as a flank mass with hypercalcemia and a high hematocrit, the best explanation is paraneoplastic production of PTH-related peptide and erythropoietin.

PTH-related peptide acts similarly to parathyroid hormone, binding the same receptors and promoting bone resorption as well as renal calcium reabsorption. This leads to increased serum calcium, producing the hypercalcemia observed. At the same time, ectopic erythropoietin production by the tumor stimulates the bone marrow to make more red blood cells, resulting in an elevated hematocrit (polycythemia).

Renal cell carcinoma is a classic tumor associated with both effects, which is why a flank mass plus these two lab findings fit perfectly. The other options don’t explain both hypercalcemia and increased red cell mass: autoimmune hemolytic processes would cause anemia rather than high hematocrit; calcitonin overproduction would lower calcium; renin overproduction doesn’t account for the calcium and red cell changes seen here.