A 58-year-old Indian man presents with a 3-month history of flank pain and gross hematuria. On examination, he has a palpable left flank mass and is found to be hypertensive (BP 160/95 mmHg). Abdominal CT shows a 6 cm heterogeneous left renal mass with areas of necrosis and calcification. Chest X-ray reveals multiple bilateral pulmonary nodules. Laboratory investigations show hemoglobin 16.5 g/dL (elevated), serum calcium 11.2 mg/dL, and normal renal function. Which of the following is the most likely histological subtype of this renal malignancy?

Explanation

## Diagnosis: Clear Cell Renal Cell Carcinoma (ccRCC) ### Clinical Presentation Analysis **Key Point:** The classic triad of flank pain, hematuria, and palpable flank mass is present in this case, though this triad occurs in only ~10% of patients and usually indicates advanced disease. ### Histological Subtype Identification The clinical and radiological features point to **clear cell RCC**: | Feature | Clear Cell RCC | Papillary RCC | Chromophobe RCC | Collecting Duct | |---------|---|---|---|---| | **Frequency** | 70–80% of RCC | 10–15% | 5% | <1% | | **Imaging** | Heterogeneous, necrosis, calcification | Solid, homogeneous | Well-circumscribed | Large, infiltrative | | **Paraneoplastic syndromes** | Common (erythropoietin, PTHrP) | Rare | Rare | Rare | | **Metastatic pattern** | Lung, bone, brain | Lung | Lung | Aggressive, early mets | | **Prognosis** | Intermediate | Better (stage-dependent) | Better | Poor | **High-Yield:** Clear cell RCC arises from the proximal convoluted tubule epithelium and accounts for ~75% of all RCC cases. The heterogeneous appearance with necrosis and calcification on imaging is characteristic. ### Paraneoplastic Manifestations **Clinical Pearl:** This patient exhibits two paraneoplastic syndromes: 1. **Erythrocytosis** (Hb 16.5 g/dL) — due to erythropoietin (EPO) production by tumor cells 2. **Hypercalcemia** (Ca 11.2 mg/dL) — due to PTHrP (parathyroid hormone-related peptide) secretion 3. **Hypertension** — from renin secretion or mass effect These paraneoplastic phenomena are most common in clear cell RCC and are associated with worse prognosis. ### Pathological Features of Clear Cell RCC **Key Point:** Histologically, clear cell RCC shows: - Cells with abundant clear cytoplasm (due to lipid and glycogen content) - Well-defined cell membranes ("chicken wire" pattern) - Increased vascularity with hemangiopericytoma-like vessels - VHL gene mutation in ~80% of cases (loss of chromosome 3p) ### Staging and Prognosis This patient has **Stage IV disease** (T3/T4, N0, M1 — pulmonary metastases). Clear cell RCC is the most common subtype to present with metastatic disease at diagnosis. **Mnemonic for RCC subtypes:** **"CCPCC"** — Clear Cell (most common), Chromophobe, Papillary, Collecting duct, Carcinoid. [cite:Robbins 10e Ch 19]