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Difficulty: MediumNeoplastic Processes

A 58-year-old man comes to the clinic reporting a two-month history of a persistent left-sided scrotal mass that feels like a 'bag of worms.' The mass does not decrease in size when he lies flat. He also reports intermittent episodes of pink-tinged urine over the past month. His past medical history is significant for a 30-pack-year smoking history, though he quit 5 years ago. His vital signs show a blood pressure of 150/95 mmHg, heart rate 82/min, and a BMI of 28 kg/m2. Physical examination confirms a left-sided varicocele that remains prominent in the supine position. Laboratory testing reveals a hemoglobin of 19.2 g/dL and a hematocrit of 58%. Which of the following best describes the molecular or pathophysiologic mechanism most directly responsible for the laboratory abnormality seen in this patient?

  1. Inappropriate stabilization of hypoxia-inducible factor leading to autonomous erythropoietin synthesisAnswer
  2. B
    Constitutive activation of Janus kinase 2 in hematopoietic stem cells
  3. C
    Physiologic compensatory erythropoiesis driven by chronic arterial hypoxemia
  4. D
    Relative hemoconcentration secondary to decreased effective circulating plasma volume
  5. E
    Ectopic production of parathyroid hormone-related peptide by malignant cells

Answer

Inappropriate stabilization of hypoxia-inducible factor leading to autonomous erythropoietin synthesis
The correct answer is inappropriate stabilization of hypoxia-inducible factor leading to autonomous erythropoietin synthesis. This patient's presentation of painless gross hematuria and a left-sided varicocele that fails to empty in the supine position is highly suspicious for a left-sided renal cell carcinoma (RCC). The left gonadal vein drains perpendicularly into the left renal vein. An RCC can extend into the renal vein, obstructing the gonadal vein and leading to a left-sided varicocele. Polycythemia (elevated hemoglobin and hematocrit) is a well-documented paraneoplastic syndrome of RCC. This occurs due to the ectopic production of erythropoietin (EPO). At the molecular level, clear cell RCCs are strongly associated with mutations in the von Hippel-Lindau (VHL) tumor suppressor gene. Loss of VHL function prevents the normal ubiquitination and degradation of hypoxia-inducible factor (HIF). The resulting inappropriate stabilization and accumulation of HIF leads to increased transcription of several target genes, including EPO, which causes secondary polycythemia.

Step-by-Step Solution

1
Analyze the physical exam findings to localize the primary lesion.
The patient has a left-sided varicocele that fails to empty when supine, alongside painless hematuria. This suggests an obstruction of the left renal vein, which the left gonadal vein drains into.
A varicocele that does not decompress raises high suspicion for a left-sided Renal Cell Carcinoma (RCC) invading the renal vein.
2
Evaluate the laboratory abnormalities in the context of the suspected lesion.
The elevated hemoglobin (19.2 g/dL) and hematocrit (58%) indicate polycythemia. In a patient with suspected RCC, this is a recognized paraneoplastic syndrome.
RCC can autonomously secrete hormones, most notably erythropoietin (EPO), causing secondary absolute polycythemia.
3
Determine the molecular mechanism underlying this specific paraneoplastic syndrome.
Ectopic EPO production in clear cell RCC is driven by mutations in the VHL tumor suppressor gene.
Loss of VHL prevents the degradation of hypoxia-inducible factor (HIF), leading to its stabilization and the subsequent autonomous transcription of EPO.

Key Concept

Renal cell carcinoma (RCC) can present with hematuria and a left-sided varicocele due to left renal vein invasion. It frequently causes paraneoplastic polycythemia due to VHL mutation-mediated stabilization of hypoxia-inducible factor (HIF), leading to autonomous erythropoietin production.
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Neoplastic Processes

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