A 69-year-old woman presents with left flank pain and hematuria. Physical examination suggests a left-sided abdominal mass. Computerized tomography (CT) scan of the abdomen reveals a 5-cm mass in the left kidney. Which of the following laboratory abnormalities might also be present?

**Core Concept**
Erythropoietin (EPO) is a hormone produced by the kidneys that stimulates red blood cell production in the bone marrow. In cases of renal cell carcinoma (RCC), EPO production is often increased due to the tumor's ability to produce this hormone.

**Why the Correct Answer is Right**
In RCC, the tumor cells can produce EPO, leading to an increase in red blood cell mass and subsequent polycythemia. This is because the tumor cells have acquired the ability to produce EPO, which in turn stimulates the bone marrow to produce more red blood cells. This is a common paraneoplastic syndrome associated with RCC.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypercalcemia is not typically associated with RCC, as this tumor often produces parathyroid hormone-related protein (PTHrP), leading to hypocalcemia.
**Option B:** Hypokalemia may occur due to renal tubular damage from the tumor or its metastases, but it is not as directly related to RCC as polycythemia.
**Option C:** Hyperuricemia may occur in RCC, especially if the tumor has metastasized to the bones, but it is not as specific a finding as polycythemia.

**Clinical Pearl / High-Yield Fact**
RCC often presents with a triad of symptoms: flank pain, hematuria, and a palpable abdominal mass. EPO production by the tumor cells can lead to polycythemia, which is a key laboratory finding in these patients.

**Correct Answer:** C.

✓ Correct Answer: A. polycythemia