A 58-year-old Indian male presents with incidental discovery of a 4 cm left renal mass on CT abdomen done for unrelated abdominal pain. Imaging shows a golden-yellow, well-circumscribed cortical lesion with heterogeneous enhancement and a tumor thrombus extending into the renal vein. Histopathology reveals the pattern marked **A** in the diagram—nests of polygonal cells with abundant clear cytoplasm separated by delicate sinusoidal vascular channels. Immunohistochemistry shows PAX8+, CA9+, and CD10+. Which of the following molecular alterations is the hallmark driver of this tumor subtype?
A. Mutation of the BAP1 gene on chromosome 3p without concurrent VHL inactivation, driving chromophobe differentiation
B. Translocation t(X;1)(p11;q21) resulting in TFE3 gene fusion and altered transcription factor activity
C. Inactivation of VHL tumor suppressor gene on chromosome 3p25, preventing HIF-1α/HIF-2α ubiquitination and leading to constitutive HIF stabilization
D. Loss of chromosome 3p and 8p with gain of chromosome 7 and 17, characteristic of papillary RCC
Explanation
Why option 1 is correct
The pattern marked A—nests of polygonal cells with abundant clear cytoplasm and delicate sinusoidal vasculature—is the hallmark microscopic appearance of clear cell renal cell carcinoma (ccRCC), the most common RCC subtype (70–75% of all RCC). The molecular hallmark is inactivation of the VHL tumor suppressor gene on chromosome 3p25, occurring in over 90% of sporadic ccRCC and in all VHL syndrome–associated cases. Loss of VHL function prevents ubiquitination and degradation of HIF-1α and HIF-2α, leading to constitutive HIF stabilization. This drives upregulation of VEGF (explaining the delicate vasculature), PDGF, EPO (paraneoplastic polycythemia), and GLUT1 (glycolysis), which together promote angiogenesis, growth, and the characteristic golden-yellow appearance due to lipid and glycogen accumulation. The presence of PAX8+, CA9+ (membranous—a HIF-driven gene), and CD10+ immunostaining further confirms ccRCC and the underlying HIF pathway activation.
Why each distractor is wrong
Option 2: TFE3 gene fusion (Xp11 translocation RCC) is characteristic of a rare, distinct RCC subtype that presents in younger patients and has different immunohistochemistry (TFE3+, often PAX8−). It does not explain the classic ccRCC morphology or the VHL-HIF axis.
Option 3: The chromosomal pattern of loss of 3p and 8p with gain of 7 and 17 is characteristic of papillary RCC, not ccRCC. Papillary RCC has a different microscopic appearance (papillary architecture with foamy macrophages, as shown in B) and is driven by MET or TFRC mutations, not VHL loss.
Option 4: While BAP1 mutations do occur on chromosome 3p and are associated with aggressive ccRCC, they are secondary drivers and occur in the context of concurrent VHL inactivation in the vast majority of cases. BAP1 loss alone is not the hallmark molecular alteration of ccRCC, and it does not drive chromophobe differentiation—BAP1-mutant tumors are still ccRCC with worse prognosis.
High-YieldNEET PG
VHL inactivation → HIF stabilization → VEGF/EPO/GLUT1 upregulation → angiogenesis, polycythemia, and the golden-yellow clear-cell phenotype. This is the central dogma of ccRCC pathogenesis and explains both morphology and paraneoplastic syndromes.
WHO Classification of Urinary Tract Tumors 5th ed; NCCN Kidney Cancer Guidelines
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