Tumor angiogenesis

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Angiogenic Switch - Flipping the Blood Flow

  • Angiogenic Switch: The process where tumors shift from an avascular to a vascular state, essential for growth beyond 1-2 mm and overcoming metabolic demands.

⭐ Tumors cannot grow beyond 1-2 mm in diameter without inducing angiogenesis, existing as dormant, in situ lesions.

  • Mechanism: Driven by an imbalance of pro- and anti-angiogenic factors.
    • Primary Trigger: Hypoxia (low oxygen).
    • Key Mediator: Hypoxia-inducible factor 1-alpha (HIF-1α) is stabilized, promoting transcription of pro-angiogenic factors (e.g., VEGF).
    • Inhibitor Loss: Inactivation of p53 decreases synthesis of anti-angiogenic molecules (e.g., thrombospondin-1).

Tumor Angiogenesis and Metastasis

Mechanism - Sprouting New Pipes

Angiogenesis is driven by an "angiogenic switch," where the balance tips in favor of pro-angiogenic factors over anti-angiogenic ones.

  • Pro-angiogenic Factors: Primarily VEGF (Vascular Endothelial Growth Factor) and bFGF (basic Fibroblast Growth Factor).
  • Anti-angiogenic Factors: Thrombospondin-1, angiostatin, and endostatin.

⭐ Vascular Endothelial Growth Factor (VEGF) is the most potent and critical mediator of tumor angiogenesis, binding to VEGFR on endothelial cells.

Mechanisms of Angiogenesis in Cancer

New tumor vessels are often leaky, tortuous, and disorganized, facilitating metastasis.

Clinical Targeting - Cutting the Supply Lines

  • Anti-VEGF Therapy: Primary strategy to inhibit tumor angiogenesis by targeting Vascular Endothelial Growth Factor (VEGF).

    • Monoclonal Antibodies: Bind to VEGF ligand.

      • Bevacizumab (Avastin)
    • Tyrosine Kinase Inhibitors (TKIs): Inhibit VEGF receptor (VEGFR) signaling within endothelial cells.

      • Sunitinib, Sorafenib

⭐ Bevacizumab (Avastin) is a monoclonal antibody that binds circulating VEGF, preventing it from activating its receptor on endothelial cells.

  • Common Side Effects:

    • Hemorrhage & bleeding
    • Hypertension
    • Impaired wound healing
    • Proteinuria & renal dysfunction
  • Resistance Mechanisms: Tumors can evade anti-VEGF therapy by upregulating alternative pro-angiogenic factors like FGF and PDGF.

High‑Yield Points - ⚡ Biggest Takeaways

  • Tumors cannot grow beyond 1-2 mm or metastasize without angiogenesis (new blood vessel formation).
  • An "angiogenic switch" occurs when pro-angiogenic factors like VEGF and bFGF overcome inhibitors.
  • Loss of p53 promotes angiogenesis by downregulating the inhibitor thrombospondin-1.
  • New tumor vessels are leaky, dilated, and haphazardly connected, which facilitates metastasis.
  • Therapeutic agents like bevacizumab are monoclonal antibodies that directly target and neutralize VEGF.

Practice Questions: Tumor angiogenesis

Test your understanding with these related questions

A research team develops a new monoclonal antibody checkpoint inhibitor for advanced melanoma that has shown promise in animal studies as well as high efficacy and low toxicity in early phase human clinical trials. The research team would now like to compare this drug to existing standard of care immunotherapy for advanced melanoma. The research team decides to conduct a non-randomized study where the novel drug will be offered to patients who are deemed to be at risk for toxicity with the current standard of care immunotherapy, while patients without such risk factors will receive the standard treatment. Which of the following best describes the level of evidence that this study can offer?

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Flashcards: Tumor angiogenesis

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Tumor cells upregulate _____ to evade anti-tumor T-cells

TAP TO REVEAL ANSWER

Tumor cells upregulate _____ to evade anti-tumor T-cells

PD-L1

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