mechanism

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.

Aggressive glioblastomas, sarcomas and gastric cancers keep amplified cancer genes such as EGFR, MYC, MDM2 and CDK4 on free-floating DNA circles (ecDNA) whose copy number rises and falls quickly, letting the tumour dial resistance up and down. Cells carrying ecDNA depend on CHK1, giving a first drug target.

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.

Tens of thousands of times a day a single DNA letter is oxidised or chemically scarred. A small crew snips it out and PARP marks the nick so it gets sealed. PARP inhibitors do not just switch PARP off; they trap it on the DNA, turning a harmless nick into a lethal break when the cell copies its DNA.

Every organ keeps its lining cells behind a thin, dense sheet of protein called the basement membrane. A tumour that has not crossed it is 'in situ' and essentially curable; crossing it is the moment cancer becomes invasive.

MYC drives half of all cancers but has no pocket for a drug and is needed by normal cells too. The first direct MYC blockers are in trials; the question is whether there is a therapeutic window.

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.

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.

Tumours come in three immune weathers: inflamed (T cells inside, checkpoint drugs work), excluded (T cells stuck at the edge), and desert (no T cells at all). Most common cancers are excluded or desert, and turning them 'hot' is the central problem of immunotherapy.

Complement is a cascade of blood proteins that punches holes in things marked by antibodies and calls in inflammatory cells. Therapeutic antibodies such as rituximab use it to kill cancer cells; tumours defend themselves with shields (CD46, CD55, CD59), and the cascade's own by-products (C5a) can recruit the myeloid cells that protect the tumour.

Nerves feed pancreatic, prostate, and other tumours. Beta-blockers and botulinum toxin are cheap, safe, and already in trials to see if severing that link slows cancer.

Before a cell divides it must copy three billion letters of DNA exactly once, 'licensing' thousands of start points in advance and firing them in waves. Cancers driven by MYC, cyclin E or RAS fire excess start points too fast, and antimetabolites such as 5-FU, topoisomerase poisons such as irinotecan and platinum drugs all jam this copying machinery.

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.

A break through both strands of DNA is the most dangerous lesion a cell faces. Two crews compete to fix it: homologous recombination copies the answer from the sister chromosome (accurate, needs BRCA), while end joining simply glues the ends (fast, sloppy). Which crew wins decides whether PARP inhibitors and radiation kill the cell.

Of the thousands of mutations in a tumour, only a handful (typically 2-8) actually drive it. Drivers either jam an accelerator on (oncogenes, one hit is enough) or remove a brake (tumour suppressors, both copies must go). Everything else is a passenger along for the ride.

Cancer cells can install pumps in their outer membrane that throw chemotherapy back out as fast as it comes in. The same pumps guard the gut, brain and bone marrow in healthy tissue, which is why blocking them failed as a strategy and why drug designers now choose payloads the pumps cannot grip.

Even when a drug wipes out 99% of a tumour, a few cells survive without any resistance mutation: they go quiet, stop dividing, and wait. These persisters are the seed of relapse. They are hard to kill precisely because they are not doing much, but they have their own weaknesses.

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.

Immune cells kill by touch: they present FAS ligand or TRAIL to a target cell, whose death receptors then trigger self-destruction from the outside in. Tumours cut this wire by deleting the receptors or over-producing decoys and blockers.

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.

Tumours recruit the body's repair cells, fibroblasts, and keep them in wound-healing mode forever. The scar tissue they lay down (desmoplasia) squeezes blood vessels shut, walls out immune cells, stiffens the tissue in a way that itself tells cancer cells to grow, and is why pancreatic cancer is so hard to treat.

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.

Several studies found patients infused with checkpoint inhibitors earlier in the day lived longer. If a randomised trial confirms it, it is a free improvement available everywhere tomorrow.

After glucose, glutamine is the tumour's favourite food. It feeds the energy cycle, donates nitrogen for making DNA letters, and makes the antioxidant glutathione. MYC- and KRAS-driven cancers eat so much of it that they starve the T cells next door.

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.

Whole regions of tissue carry cancer mutations long before a tumour exists. Detecting and treating the field, not the tumour, could prevent cancers rather than cure them.

Getting into the bloodstream and surviving there is brutal: cells are ripped from their neighbours, battered by flow, and hunted by NK cells. Fewer than one in a thousand survive. The ones that do travel in clusters, wear a cloak of platelets, or ride with neutrophils. Liquid biopsies catch what is left.

To invade, a cancer cell must grip the scaffolding around it, dissolve a path with enzymes, and pull itself forward, alone or in a chain led by a scout cell. Fibroblasts often cut the trail first. The enzyme blockers of the 1990s failed; today's targets are the grip (integrins, FAK) and the trail-makers.

Most cancers have the wrong number of chromosomes; normal cells do not. If that difference creates a specific weakness, a drug against it would spare normal tissue by definition.

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.

Instead of trying to kill every hidden cancer cell after surgery, keep them dormant for life with low-toxicity drugs, the way extended hormone therapy already does in breast cancer.

The cells that survive targeted therapy change shape and become unusually dependent on an antioxidant enzyme, GPX4. Hitting them in that window might stop resistance before it evolves.

Under pressure from a drug that blocks its identity (the androgen receptor in prostate cancer, EGFR in lung cancer), a tumour can change what kind of cell it is, becoming a small-cell neuroendocrine cancer that no longer needs the blocked signal. It is the ultimate escape: not a new mutation in the engine, but a new engine.

Dividing cells need membranes, and membranes are fat. Cancers switch on the fat-building enzymes most adult tissues keep off, and in fatty environments (breast, omentum, bone marrow) they also steal lipids from neighbouring fat cells. This links obesity to cancer and offers new drug targets.

Metabolic drugs keep failing because tumours switch fuels. Measuring what a patient's tumour actually eats, with tracers and PET, could pick the right metabolic drug for the right tumour.

Stool transplants from immunotherapy responders have rescued some non-responders in melanoma. If defined bacterial cocktails work as well, every immunotherapy patient could get one.

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.

After DNA is copied, a proofreading crew fixes the letters the polymerase got wrong. Lose it and the genome fills with thousands of small errors, especially in repetitive stretches (microsatellites). Those errors make abnormal proteins that the immune system can see, which is why immunotherapy works so well in these cancers.

When a cell divides, a scaffold of microtubules (the spindle) pulls one copy of each chromosome to each side. A checkpoint holds the split until every chromosome is hooked on. Taxanes and vinca alkaloids freeze the spindle so the cell is stuck at this checkpoint until it dies.

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.

Every cause of DNA damage leaves its own fingerprint in the genome: sunlight, tobacco, a faulty repair enzyme, a gut bacterium. Reading these fingerprints tells you what caused a cancer and which repair crews it is missing, which in turn predicts which drugs will work.

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.

Tumours recruit the body's clean-up cells (macrophages and immature myeloid cells) and re-train them as bodyguards. They switch off T cells, build vessels, and, when a therapeutic antibody flags a cancer cell for eating, are told 'don't eat me' by CD47 on its surface.

Natural killer cells patrol for cells that have lost their identity papers (MHC-I) or that display stress flags. Cancers that hide from T cells by dropping MHC-I become visible to NK cells, unless they also shed the stress flags, wrap themselves in a second inhibitory badge (HLA-E), or soak the neighbourhood in TGF-β.

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.

Tumours and immune cells eat from the same plate. Cancer cells hoard glucose and glutamine, dump lactate and acid, and burn tryptophan and arginine into by-products that paralyse T cells. The tumour wins the food fight, and the immune system loses before it has fired a shot.

About one cancer in eight worldwide is caused by a virus. HPV, hepatitis B and C, Epstein-Barr, HTLV-1, KSHV and Merkel cell polyomavirus each hijack the same brakes cancer normally has to mutate, which is why vaccines against HPV and HBV are among the most effective anti-cancer drugs ever made.

Chemotherapy leaves behind senescent cells that inflame tissues and help tumours relapse. A short course of senolytic drugs afterwards might reduce relapse and long-term side effects at once.

Breast cancer goes to bone, lung, liver and brain; prostate cancer to bone; colon cancer to liver; uveal melanoma almost only to liver. Paget's 1889 idea still holds: where a cancer spreads depends on both the seed (the cell's programme) and the soil (the organ's welcome). Each soil has its own vicious cycle, and some are druggable.

Growth-factor receptors are antennas on the cell surface that pair up when a signal lands and switch on the growth relays inside. Cancers mutate, multiply, or fuse these antennas so they broadcast 'grow' with no signal at all. Most targeted drugs, antibodies and ADCs start here.