# The angiogenic switch & tumour vessels

Source: https://onco.cc/pathways/angiogenic-switch/  
OnCo record `angiogenic-switch` (Pathway). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A tumour cannot grow beyond a couple of millimetres without its own blood supply. The 'switch' flips when the signals calling for new vessels (VEGF, FGF, angiopoietin) outweigh the ones holding them back (thrombospondin). The vessels that result are leaky and chaotic, which starves the tumour of oxygen, blocks drugs, and gives cancer cells a way out.

## Summary

Hypoxia (HIF), oncogenes (RAS, MYC), p53 loss (which normally induces thrombospondin-1) and inflammatory cells tip the balance of pro-angiogenic (VEGF-A/C, FGF2, PDGF-B, ANG2, PlGF) over anti-angiogenic (TSP-1, endostatin, angiostatin) factors. Endothelial tip cells (VEGFR2, DLL4-Notch selection) sprout, stalk cells proliferate, pericytes (PDGFRβ) stabilise; ANG2 destabilises. Alternatives: vessel co-option (liver, lung, brain metastases; a mechanism of bevacizumab resistance), intussusception, vasculogenic mimicry, and bone-marrow-derived endothelial progenitors. Tumour vessels are tortuous, leaky, poorly pericyte-covered and lack hierarchy, producing heterogeneous hypoxia, acidity, high interstitial pressure (which collapses vessels further and blocks drug penetration), and easy intravasation. Anti-VEGF therapy at moderate doses 'normalises' vessels transiently, improving perfusion, drug delivery and T-cell entry, the basis of IO-VEGF combinations. Resistance: alternative ligands (FGF, ANG2, PlGF), myeloid cells, co-option, and increased invasiveness.

## Fields

- Kind: Pathway
- Last checked: 2026-09-09
- Tags: mechanism; mechanics-atlas
- Analogy: A new housing estate demanding roads. Once the developers (VEGF) outvote the planners (thrombospondin), roads are laid overnight: badly, with dead ends and potholes, so deliveries (oxygen, drugs) fail and the estate's residents can slip out onto the motorway. Anti-VEGF drugs do not close the roads; used well they make the few that remain drivable.
- Interventions: Anti-VEGF antibodies (bevacizumab, ramucirumab) and VEGFR TKIs (axitinib, cabozantinib, lenvatinib, sunitinib, pazopanib, tivozanib, fruquintinib, regorafenib, sorafenib); Vascular normalisation windows for IO-VEGF combinations in RCC, HCC, endometrial cancer; PD-1×VEGF bispecific ivonescimab; HIF-2α inhibition upstream (belzutifan); multikinase inhibitors hit FGFR/PDGFR escape ligands; Vessel co-option limits anti-angiogenics in liver and brain metastases

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Angiogenesis
- Bergers & Benjamin, Tumorigenesis and the angiogenic switch (Nat Rev Cancer 2003): https://doi.org/10.1038/nrc1093

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Glioma & glioblastoma](https://onco.cc/cancers/glioblastoma/), [Hepatocellular carcinoma](https://onco.cc/cancers/hcc/), [Ovarian cancer](https://onco.cc/cancers/ovarian/), [Renal cell carcinoma](https://onco.cc/cancers/rcc/)
- technologies: [Anti-angiogenic therapy](https://onco.cc/technologies/antiangiogenic/), [Hypoxia-activated prodrugs](https://onco.cc/technologies/hypoxia-activated-therapy/), [Small-molecule kinase inhibitors](https://onco.cc/technologies/kinase-inhibitors/)
- targets: [CSF1R](https://onco.cc/targets/csf1r/), [FGF13](https://onco.cc/targets/fgf13/), [FGF2](https://onco.cc/targets/fgf2/), [HIF-1α (HIF1A)](https://onco.cc/targets/hif1a/), [HIF-2α](https://onco.cc/targets/hif2a/), [PD-1](https://onco.cc/targets/pd1/), [PDGFRA](https://onco.cc/targets/pdgfra/), [VEGF / VEGFR](https://onco.cc/targets/vegf/)
- drugs: [Axitinib](https://onco.cc/drugs/axitinib/), [Belzutifan](https://onco.cc/drugs/belzutifan/), [Bevacizumab](https://onco.cc/drugs/bevacizumab/), [Cabozantinib](https://onco.cc/drugs/cabozantinib/), [Fruquintinib](https://onco.cc/drugs/fruquintinib/), [Ivonescimab](https://onco.cc/drugs/ivonescimab/), [Lenvatinib](https://onco.cc/drugs/lenvatinib/), [Nintedanib](https://onco.cc/drugs/nintedanib/), [Pazopanib](https://onco.cc/drugs/pazopanib/), [Ramucirumab](https://onco.cc/drugs/ramucirumab/), [Regorafenib](https://onco.cc/drugs/regorafenib/), [Sorafenib](https://onco.cc/drugs/sorafenib/), [Sunitinib](https://onco.cc/drugs/sunitinib/), [Tivozanib](https://onco.cc/drugs/tivozanib/)
- pathways: [Intravasation & circulating tumour cells](https://onco.cc/pathways/intravasation-ctc-survival/), [Myeloid suppression: TAMs, MDSCs & don't-eat-me signals](https://onco.cc/pathways/myeloid-suppression-axis/), [Tumour microenvironment (TME)](https://onco.cc/pathways/tumor-microenvironment/), [VEGF angiogenesis](https://onco.cc/pathways/vegf-angiogenesis/), [VHL / HIF oxygen sensing](https://onco.cc/pathways/hif-vhl/)
- terms: [Hallmark: inducing or accessing vasculature](https://onco.cc/terms/inducing-angiogenesis/), [Microenvironment and inflammation: tumours as wounds that do not heal](https://onco.cc/terms/microenvironment-inflammation-theory/)
- key papers: [Tumorigenesis and the angiogenic switch](https://onco.cc/key-papers/paper-bergers-nat-rev-cancer/)

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