A 62-year-old man with a 35-pack-year smoking history and occupational exposure to trichloroethylene presents with painless gross hematuria, right flank pain, a palpable right flank mass, fatigue, and 6 kg weight loss over 3 months. Laboratory investigations show hemoglobin 17.8 g/dL, calcium 11.6 mg/dL, and elevated LDH. Multiphasic contrast-enhanced CT of the abdomen is performed. The structure marked **A** in the diagram—a heterogeneously enhancing exophytic right renal mass measuring 8 cm with avid arterial-phase enhancement and central necrosis—is most consistent with which histological subtype of renal cell carcinoma?

Question

Accepted Answer

D. Clear cell renal cell carcinoma (70–80% of RCC cases). ## Why Clear cell renal cell carcinoma (70–80% of RCC cases) is right

The structure marked **A**—a heterogeneously enhancing exophytic renal mass with **avid arterial-phase enhancement** and central necrosis—is the hallmark imaging signature of clear cell RCC (ccRCC). Clear cell carcinoma accounts for 70–80% of all RCC cases and is characterized by its hypervascular nature, resulting in intense arterial-phase enhancement on multiphasic CT. The rapid contrast washout on delayed phases, heterogeneous enhancement (due to intratumoral necrosis and hemorrhage), and exophytic growth pattern are all typical of ccRCC. The clinical presentation—paraneoplastic erythrocytosis (hemoglobin 17.8 g/dL from ectopic erythropoietin), hypercalcemia (calcium 11.6 mg/dL from PTHrP), and elevated LDH—further supports ccRCC, which is the most common source of paraneoplastic syndromes among RCC subtypes. [Motzer RJ et al. NCCN Clinical Practice Guidelines, 2022]

## Why each distractor is wrong

- **Papillary renal cell carcinoma**: Papillary RCC typically shows **less avid arterial enhancement** compared to clear cell RCC and is less hypervascular. It accounts for only 10–15% of RCC cases and is less commonly associated with paraneoplastic erythrocytosis and hypercalcemia. The imaging pattern of **A** is inconsistent with papillary subtype.
- **Chromophobe renal cell carcinoma**: Chromophobe RCC (5% of RCC) is typically **less hypervascular** than clear cell RCC and shows more homogeneous enhancement. It rarely presents with the degree of arterial-phase hyperenhancement and central necrosis seen in structure **A**. Paraneoplastic syndromes are uncommon with chromophobe RCC.
- **Oncocytoma**: Although oncocytoma is a benign renal tumor that can show arterial enhancement, it is **not a malignant RCC subtype**. Oncocytomas are typically more homogeneous, lack central necrosis, and do not cause the paraneoplastic syndromes (erythrocytosis, hypercalcemia) observed in this patient. The presence of metastatic disease and venous thrombus excludes benign oncocytoma.

**High-Yield:** Clear cell RCC = hypervascular + avid arterial enhancement + paraneoplastic syndromes (erythrocytosis, hypercalcemia, Stauffer syndrome) = 70–80% of all RCC.

[cite: Motzer RJ et al. Kidney Cancer, Version 3.2022, NCCN Clinical Practice Guidelines. J Natl Compr Canc Netw 2022;20(1):71-90.]

Answer

A. Papillary renal cell carcinoma

Answer

B. Oncocytoma

Answer

C. Chromophobe renal cell carcinoma

Explanation

Why Clear cell renal cell carcinoma (70–80% of RCC cases) is right

Why each distractor is wrong

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