Pathways

Androgen receptor signalling is prostate cancer's engine. Testosterone becomes DHT, binds the androgen receptor, and drives growth genes. Castration removes the fuel; newer pills block the receptor or the enzyme that makes fuel inside the tumour.

How the immune system sees cancer, and how cancer learns to hide. Tumours display fragments of their proteins on MHC molecules; T cells kill the ones they recognise; the survivors are the ones that stopped showing fragments or switched on brakes.

Autophagy is the cell's recycling programme. Cancer cells, especially pancreatic and RAS-driven tumours, use it to survive starvation and drug stress, which is why hydroxychloroquine, an old malaria drug that blocks it, keeps appearing in trials.

The wasting syndrome that kills up to a third of cancer patients: tumours send hormonal signals (GDF-15, IL-6) that switch off appetite and burn muscle and fat. The first drug to reverse it, ponsegromab, showed weight gain in 2024.

Cancer cells rewire how they eat. They burn glucose inefficiently but fast (the Warburg effect), gorge on glutamine and fats, and build the nucleotides and lipids needed to divide. This is why the FDG PET scan works, and why metabolism is a drug target.

Cancer neuroscience is the study of how tumours talk to nerves. Nerves grow into tumours and feed them signals; brain tumours even wire themselves into neural circuits. Cutting the conversation with common drugs such as beta-blockers is now being tested.

Some cancer cells behave like stem cells: they can regrow the whole tumour, resist treatment, and switch identities. This plasticity explains why tumours come back and why some lung and prostate cancers transform into a different cancer type under therapy.

Damaged cells can stop dividing permanently instead of dying. That protects against cancer at first, but senescent cells linger, secrete inflammatory signals, and after chemotherapy can help tumours relapse, so removing them (senolytics) is a new strategy.

cGAS-STING is the cell's alarm for DNA in the wrong place. Radiation, chemotherapy, and ADCs spill DNA into the cytoplasm; cGAS detects it, STING sounds the alarm, and interferon calls in the immune system.

Most cancers have the wrong number of chromosomes and keep shuffling them at every division. This chaos fuels evolution and drug resistance, but it also stresses the cell and can trigger immune alarms, a double edge that researchers are trying to exploit.

Cells run on a 24-hour clock that gates cell division, DNA repair, and drug metabolism. Cancers often break their clocks, and the time of day a drug or immunotherapy is given can change how well it works.

A tumour is a population that evolves by natural selection. Treatment kills the sensitive cells and selects the rest, which is why resistance is the rule; measuring the surviving population (MRD) and adapting therapy is the counter-strategy.

As we age, blood stem cells with cancer-like mutations quietly expand in most people. These clones raise leukaemia and heart disease risk, are accelerated by chemotherapy, and confuse blood tests for cancer DNA.

The DNA damage response is the cell's set of repair crews. Single-strand breaks are patched by PARP; double-strand breaks by BRCA-dependent homologous recombination. Lose one crew and the cell survives; lose both and it dies. That is how PARP inhibitors work.

Cancers copy their DNA too fast and with broken checkpoints, so replication forks stall and collapse. They survive only by leaning on emergency repair kinases such as ATR, CHK1, and WEE1, which is why blocking those kinases can be selectively lethal.

Cancer changes not just its genes but how they are read: chemical tags on DNA and histones silence guardians and awaken growth programmes. Unlike mutations, these changes are reversible, which is the hope behind epigenetic drugs.

How a cancer cell changes shape to migrate and to shrug off drugs. Transcription factors like ZEB1 and SNAIL loosen the cell, switch on pumps that eject chemotherapy, and hide it from the immune system.

Cells can die in several programmed ways. Beyond the classic apoptosis, ferroptosis kills through iron-driven fat oxidation, and drug-resistant, mesenchymal cancer cells turn out to be unusually prone to it.

Cancer often arises from a whole region of tissue that already carries mutations, not from one rogue cell. Sun-exposed skin, smokers' airways, and Barrett's oesophagus are patchworks of mutant clones competing long before a tumour appears.

A developmental pathway that shapes embryos and is switched back on in basal cell skin cancer and some brain tumours. Blocking it cures most advanced basal cell carcinomas, but tumours learn to reactivate it downstream.

The pathway that tells organs when to stop growing. Cancers disable it so YAP and TAZ stay in the nucleus driving growth; in mesothelioma, NF2 loss does exactly that, and the first drugs against the YAP–TEAD switch are in trials.

Chronic inflammation is soil for cancer: it feeds growth signals, DNA damage, and immune suppression. The NF-κB switch inside cells is the master relay, and colitis, hepatitis, and H. pylori gastritis are the clinical proof.

Intrinsic apoptosis is the cell's self-destruct switch. BCL-2 holds it shut; BAX and BAK pull it open. Venetoclax pries BCL-2 off so the switch can fire.

The relay that turns cytokine signals into gene changes. Overactive in blood cancers (JAK2 in myelofibrosis), it is also the wire that carries interferon's cancer-killing message, so tumours cut it to escape immunotherapy.

KEAP1–NRF2 is the cell's antioxidant defence switch. Lung cancers often break the off-switch (KEAP1), leaving NRF2 permanently on, which detoxifies chemotherapy and radiation and makes these tumours resistant to almost everything.

The bacteria in the gut, and even inside tumours, influence whether cancer starts and whether immunotherapy works. Transplanting stool from responders has made some non-responders respond.

Cancer cells must make protein at furious speed. The eIF4F complex that starts protein synthesis is the funnel where growth signals converge, and drugs that pinch the funnel starve the tumour of the proteins it needs most.

MYC is the most commonly amplified cancer gene, a master switch that turns on thousands of growth genes. It has no pocket for a conventional drug, so it remained 'undruggable' for 40 years; the first direct MYC drugs finally entered trials in the 2020s.

A cell-to-cell contact signal that decides cell fate. It drives T-cell leukaemia when mutated on, acts as a tumour suppressor in some squamous cancers when lost, and its ligand DLL3 became a drug target in small-cell lung cancer.

In hormone-positive breast cancer, oestrogen binds its receptor, which switches on genes that make the cell divide. Every endocrine therapy cuts this chain somewhere.

The p53 and RB checkpoints are the cell's brakes. p53 senses damage and stops the cell from copying itself; RB holds the cell at the G1 gate until CDK4/6 unlocks it. Cancers cut these brakes.

How T cells decide to attack. A T cell needs to see the target (TCR-MHC) and get a 'go' signal (CD28). PD-1 and CTLA-4 are 'stop' signals; tumours exploit them. Checkpoint inhibitors remove the stop.

The cell's 'grow and survive' circuit. Growth signals from the surface switch on PI3K, which switches on AKT, which switches on mTOR, which builds proteins and blocks self-destruction.

The RAS-MAPK pathway is the cell's 'divide' relay. A signal at the surface flips RAS on, which passes to RAF, MEK, and ERK, which tell the nucleus to make the cell divide. KRAS and BRAF mutations jam it in the on position.

Genes are cut and pasted into messages before they are used. Blood cancers often carry mutations in the splicing machinery, and the errors create abnormal proteins that could serve as targets or immune flags.

A machine that opens and closes DNA so genes can be read. One in five cancers has a broken part (ARID1A, SMARCA4, PBRM1), and losing one part often creates a dependence on its twin, which is the basis for new synthetic-lethal drugs.

Normal cells can divide only so many times because the protective caps on their chromosomes, telomeres, wear down. Cancers switch the cap-rebuilding enzyme telomerase back on, or find another way (ALT), so they can divide forever.

A signal that stops normal cells from dividing but, once a cancer is established, switches sides: it builds scar-like stroma, walls out immune cells, and pushes cells into a migratory state.

How cancer spreads: cells leave the tumour, squeeze into blood or lymph vessels, survive the journey, exit into a new organ, often sleep there for years, and finally grow. Metastasis causes about 90% of cancer deaths.

Cancer cells can hide in bone marrow, lung, or brain for years or decades, asleep and invisible to scans and chemotherapy, then wake up. Late relapse in breast and prostate cancer is dormancy ending.

A tumour is not just cancer cells. It is a neighbourhood of fibroblasts, immune cells, blood vessels, nerves, and scaffolding that the cancer recruits and corrupts, and that decides whether drugs and immune cells can get in.

How tumours grow their own blood supply. Low oxygen makes cells release VEGF, which tells blood-vessel cells to sprout toward the tumour.

The VHL/HIF pathway is how cells sense oxygen (the 2019 Nobel Prize). VHL destroys HIF when oxygen is present. Kidney cancers lose VHL, so HIF-2α is permanently on and drives blood vessel growth and proliferation.

Wnt/β-catenin is a developmental pathway hijacked by colorectal cancer. Normally a destruction complex keeps β-catenin low; losing APC lets it flood the nucleus and drive growth genes.