A 68-year-old man with a 40-year smoking history and hypertension is found to have a left renal mass on incidental CT imaging. Histopathological examination reveals nests of large cells with abundant clear cytoplasm separated by a delicate branching capillary network, as marked by **A** in the diagram. Which of the following molecular alterations is the PRIMARY driver of the characteristic hypervascular phenotype in this tumor?
A. Mutation of PBRM1 gene causing loss of chromatin remodeling capacity
B. Translocation t(X;1)(p11;q21) resulting in TFE3 fusion and altered transcriptional regulation
C. Amplification of MET proto-oncogene resulting in enhanced hepatocyte growth factor signaling
D. Inactivation of VHL tumor suppressor gene leading to constitutive HIF-1α/HIF-2α stabilization and VEGF upregulation
Explanation
Why option 1 is correct
The structure marked A — nests of clear cytoplasm cells — is the defining histologic hallmark of clear cell renal cell carcinoma (ccRCC). The molecular hallmark of ccRCC is inactivation of the VHL tumor suppressor gene on chromosome 3p25 (present in ~80–90% of sporadic ccRCC cases). VHL loss leads to constitutive stabilization of hypoxia-inducible factors (HIF-1α and HIF-2α), which transcriptionally upregulate VEGF, PDGF, and TGF-α. This drives the characteristic hypervascular phenotype — the delicate branching capillary network (chicken-wire pattern) seen in the diagram — and forms the molecular rationale for anti-angiogenic therapy (VEGF TKIs, anti-VEGF antibodies, and checkpoint inhibitors). This is the PRIMARY and most common molecular driver of ccRCC pathogenesis (WHO Classification of Urinary & Male Genital Tumors 5e, NCCN Kidney Cancer Guidelines).
Why each distractor is wrong
Option 2 (MET amplification): While MET alterations occur in some renal cancers (particularly hereditary papillary RCC type 1), they are not the primary driver of the ccRCC phenotype. MET-driven tumors typically present with a papillary morphology, not the clear cell pattern marked as A.
Option 3 (PBRM1 mutation): PBRM1 is a BAF180 chromatin remodeling gene that is mutated in ~40% of ccRCC cases, but it is a secondary/co-driver mutation, not the primary initiating event. PBRM1 loss does not directly explain the hypervascular phenotype or the clear cell morphology.
Option 4 (TFE3 translocation): TFE3 fusions (e.g., t(X;1)(p11;q21)) are characteristic of translocation renal cell carcinoma (tRCC), a distinct entity with different morphology (epithelioid cells, voluminous cytoplasm, papillary architecture). This is not the molecular basis of ccRCC.
High-YieldNEET PG
VHL inactivation → HIF stabilization → VEGF upregulation → hypervascular ccRCC; this is the molecular basis for why anti-angiogenic therapy (sunitinib, pazopanib, axitinib, cabozantinib) and checkpoint inhibitors work in metastatic ccRCC.
WHO Classification of Urinary & Male Genital Tumors 5e; NCCN Kidney Cancer Guidelines
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