Mechanics of cancer

A shop floor with a locked glass floor beneath it. Staff (epithelial cells) can be unruly upstairs and it is still contained; the emergency begins when someone cuts through the glass into the building services below, where the plumbing (blood and lymph vessels) runs.

A building inspector (Hippo) who checks that the block is full and stops new floors. Cancers fire the inspector, and the architect (YAP/TAZ) keeps adding storeys.

A relay of seven runners. The race is only won if every baton is passed. Cancers usually drop only one or two batons, so the treatment that works is the one that fixes the step that actually failed, which is why the same drug cures one patient and does nothing for the next.

Wanted posters: the cell pins fragments of everything it makes onto its surface. Immune police recognise criminals' faces. Cancers that survive have taken down the posters (lost MHC) or bribed the police (checkpoints).

A checkpoint at a border: p53 is the inspector who halts traffic when something looks wrong, MDM2 is the manager who keeps sending the inspector home, RB is the barrier arm, and CDK4/6 is the motor that lifts it. Cancers bribe the inspector (TP53 mutation) or hot-wire the motor (cyclin D amplification).

Two repair crews for a road: PARP fixes potholes, BRCA rebuilds collapsed bridges. A town that has lost its bridge crew (BRCA mutation) survives as long as potholes are fixed before they become bridge collapses. Block the pothole crew (PARP inhibitor) and the bridges fall.

A dam (mitochondrial membrane) held by guards (BCL-2, MCL-1) against demolition crews (BAX/BAK). Cancer hires extra guards. Venetoclax fires the BCL-2 guards, and the dam breaks.

A doorbell wired to a self-destruct switch: immune cells ring it. Some tumours rip out the doorbell (FAS loss), some stuff the wiring with insulation (c-FLIP), and some install a second doorbell that rings nowhere (decoy receptors).

Retired workers who refuse to leave the office. They no longer do the job, but they shout, clutter the corridors, and sometimes hire back the very people who were fired.

A fire marshal who is normally kept locked in a cupboard (by MDM2). When alarms sound, the cupboard opens and the marshal stops work, calls repairs, and if the building is beyond saving, orders evacuation (apoptosis) or condemns it (senescence). Cancers either sack the marshal (TP53 mutation) or weld the cupboard shut (MDM2 amplification).

The plastic tips on shoelaces fray a little every time you tie them; when they are gone the lace unravels and the shoe is thrown out. Cancer cells carry a machine that keeps re-tipping the laces.

Footprints in snow. A fox, a dog and a child each leave a distinct print; you can tell who crossed the garden without having seen them. Cancer genomes are snowfields, and each mutagen and each broken repair crew leaves its own print.

A car with a stuck accelerator (oncogene: one fault is enough) and cut brake lines (tumour suppressor: both lines must fail because they are duplicated). The scratches on the paintwork (passengers) did not cause the crash but they tell you what road it drove on.

Clonal evolution is like weeding a field with one herbicide year after year: the field fills with the one weed that shrugs it off. Rotating herbicides and leaving some susceptible weeds to crowd out the resistant ones is the evolutionary alternative.

Weeds in the blood's seed bank. Harmless individually, they spread with age and after chemical sprays, some turn into leukaemia, and their DNA litters the blood, so a test for tumour DNA can mistake weeds for cancer.

The genome is the book; epigenetics is the highlighting and the pages stapled shut. Cancer staples shut the safety chapters and highlights the growth chapters. Epigenetic drugs pull staples.

A librarian who unlocks shelves on request. When one librarian is fired the other covers both shifts; fire the second and the library stops working. That second librarian is the drug target.

A lawn where many patches have already turned to weeds. Any single tumour is one patch that took over; mowing it leaves the rest of the lawn ready to sprout again.

A burglar who does not need to pick the locks because he carries a master key: E6 and E7 are keys that open p53 and RB directly, saving the virus the years of mutation a spontaneous cancer needs. The upside is that the burglar's face is on every camera, so the immune system can be taught to spot him.

A wound that never heals: the repair crews keep pouring in growth signals and clearing away rubble, and a wound that is always being rebuilt is a wound where mistakes accumulate.

An engine with four cylinders that must fire in sequence. Cyclins are the fuel injected into each cylinder in turn and burned away; CDKs are the pistons. p16 and p21 are the hand on the throttle. Cancers flood the first cylinder (cyclin D) or remove the throttle hand (CDKN2A).

Printing a 3,000-page book on thousands of small presses at once. Licensing hands out one ticket per press before printing begins; firing starts them in waves. Cancer starts far too many presses with too little ink (nucleotides), so pages smear and tear, and many chemotherapies simply cut off the ink supply or jam the rollers.

A photocopier running at triple speed with the paper-jam sensor removed. It keeps working only because a technician (ATR/CHK1/WEE1) constantly clears jams. Remove the technician and it destroys itself.

A tug-of-war where the referee (spindle checkpoint) will not blow the whistle until every player has a grip on the rope. Taxanes glue the rope so nobody can pull; the match never starts and the players eventually collapse. Cells without p53 sneak off the pitch with the wrong number of players, which is how aneuploidy begins.

Chromosomal instability is a library that reshuffles and duplicates random shelves every night. Most rearrangements are useless, some ruin the building, but occasionally one yields a book the librarian needs to survive a new rule, and the mess itself keeps the fire alarms twitching.

Two halves of a walkie-talkie that only transmit when clipped together by a signal from outside. Cancer glues them together (fusions, mutations) or installs hundreds of extra sets (amplification), so the room is full of shouted 'grow' orders. TKIs pull the battery, antibodies tape over the microphone, ADCs use the aerial as a mailing address for poison.

A relay race: receptor hands the baton to RAS, RAS to RAF, RAF to MEK, MEK to ERK, ERK runs into the nucleus and shouts 'divide'. A KRAS mutation is a runner who never stops running whether or not anyone handed them the baton.

Think of a factory: the receptor is the order desk, PI3K and AKT are the managers relaying the order, PTEN is the accountant cancelling orders, and mTOR is the assembly line. Cancer forges orders (PIK3CA mutation) or fires the accountant (PTEN loss).

A conductor who can make every section of the orchestra play louder at once. You cannot take away the baton, so drugs try to silence the score (transcription), tire the conductor (degradation), or exploit the fact that a full-volume orchestra cannot afford a single missing player.

A concert where a few songs are played at deafening volume through rented amplifiers. Cutting the mains for a moment (BET, CDK7/9 inhibitors) silences the loudest songs first because their sound decays fastest, while the quieter household appliances keep humming.

A factory's single loading dock (eIF4F). No matter how many orders the managers (RAS, PI3K, MYC) shout, everything must pass through the dock. Narrow the dock and the most urgent, oversized orders (oncogene proteins) are the first to fail.

A recycling plant with barcode stickers (ubiquitin) and a shredder (proteasome). Myeloma is a paper mill that produces so much waste it dies when the shredder stops (bortezomib). PROTACs and glues are forged stickers that get the plant to shred the cancer's own machinery.

A torn page. The careful archivist (HR) fetches the twin copy from the shelf and transcribes it letter for letter; the hurried clerk (NHEJ) tapes the two halves together, losing a few words. Tumours missing the archivist survive on the clerk, so anything that adds more torn pages (PARP inhibitors, platinum, radiation) buries them.

A spell-checker that runs after every page is typed. Without it, typos pile up, especially in words like 'banana' where it is easy to lose count of the repeats. The garbled words in the resulting proteins read as foreign, so the immune system, once its brakes are released, attacks with unusual vigour.

A besieged city that starts recycling furniture into firewood. It keeps the lights on through the siege, and burning the 'wanted posters' (MHC) hides its criminals too.

Ferroptosis is rust. Iron plus oxygen eats through the cell's membranes unless an antioxidant crew (GPX4) keeps repainting them. Cells that changed shape to dodge chemotherapy have thinner paint.

KEAP1–NRF2 is a smoke detector wired to a sprinkler system. Cancers jam the detector on, so the sprinklers run constantly and wash away every poison you throw at them.

A factory that switches from a clean, efficient power plant to burning everything it can find, fast and dirty, because speed matters more than efficiency when you are building a new factory every day.

A construction site that runs on two deliveries: sand (glucose) for bulk and steel (glutamine) for the frame and the rebar. MYC doubles the steel order. Cutting one delivery rarely stops the build because the site switches suppliers; that is why single metabolic drugs have disappointed.

A factory that must build its own walls. Normal adult tissue buys wall panels from a supplier (dietary fat); cancer reopens its own panel plant (FASN) and, when it lands in a fat depot, simply strips panels off the buildings next door.

VHL is the shredder that destroys the 'we are suffocating' memo whenever there is oxygen around. Kidney cancer breaks the shredder, so the memo piles up and the cell keeps ordering new blood vessels and sugar.

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.

A growing town (tumour) that keeps sending out road-building orders (VEGF). Anti-angiogenic drugs cancel the orders; at the right dose the roads that remain are straighter and better, so police (immune cells) and supplies (drugs) get in.

A buffet where the tumour arrives first, eats the protein, and leaves the table sticky with lactate. The immune guests arrive hungry and find nothing but by-products that make them drowsy.

A soldier needs a target in the sights (TCR) and an order to fire (CD28). CTLA-4 is a commander revoking orders during training; PD-1 is a white flag the enemy waves on the battlefield that makes the soldier lower their weapon. Checkpoint inhibitors tear up the white flag.

A soldier posted at a wall for months with no relief. First tired, then unwilling to fire, finally unable to, and the last stage is written into their habits so deeply that no order can undo it. Checkpoint inhibitors work on the tired, not the broken.

Three kinds of town: one where the police already patrol the streets (inflamed), one where they mill about outside a wall (excluded), and one with no police station at all (desert). Removing the officers' handcuffs (PD-1 blockade) only helps in the first; the second needs a gate, the third needs recruitment.

A smoke detector wired to the fire brigade. DNA in the cytoplasm is smoke; cGAS is the detector; STING is the alarm bell; interferon is the 999 call that brings the immune system. Many tumours have quietly removed the batteries.

A landlord who hires the neighbourhood's own bouncers, pays them in sugar and lactate, and hangs a sign on every door that reads 'don't touch, friend' (CD47). The police (T cells) are stopped at the door by the bouncers, and the cleaners (macrophages) read the sign and leave.

A castle under siege from the inside: the cancer conscripts the town's builders (fibroblasts) to raise walls, bribes the guards (macrophages) to look away, and diverts the water supply (vessels) so that reinforcements (T cells, drugs) never arrive.

A town planner who first refuses all new building (tumour suppressor) and then, corrupted, builds walls and moats around the tumour that keep the police out (immune exclusion).

A demolition crew that follows the flags an antibody plants on a building: they blow holes in the walls (membrane attack complex) and call in the bulldozers (phagocytes). Tumours paint over the flags (CD55, CD59), and the noise of the demolition attracts the wrong kind of crowd (C5a-recruited suppressor cells).

Guards who stop anyone not wearing a staff badge (MHC-I) or anyone visibly panicking (stress ligands). Cancer's trick against T cells (throwing away the badge) makes it conspicuous to these guards, so successful tumours also learn to stop panicking, borrow a visitor badge (HLA-E) and bribe the guards with TGF-β.

A brick in a wall (epithelial cell) turning into a nomad: it lets go of its neighbours, packs pumps to spit out poison, and puts on camouflage. The wall-brick was easy to hit; the nomad is not.

A climber in a collapsing tunnel: grip the wall (integrins), chip away the rock ahead (MMPs), and haul forward (myosin). Some climbers squeeze through cracks without chipping (amoeboid). Often a guide (a fibroblast) has already carved the passage.

Leaving a fortress through the drains and swimming a river in flood while archers (NK cells) fire from the bank. Survivors go in rafts (clusters), under wet blankets (platelets), and with a friendly escort (neutrophils).

A colonising power that sends engineers, seed and fertiliser to a distant shore before the settlers sail. The settlers (CTCs) that land where the soil has been prepared survive; the ones that land elsewhere starve.

A seed leaving a plant: it must detach, ride the wind, land somewhere with the right soil, survive the winter, and only then sprout. Almost every seed fails; the few that grow are the metastases.

Seeds that stay in the soil for years waiting for the right spring. You can keep the ground cold (maintenance therapy), force them to sprout and mow them (wake-and-kill), or dig them out (immune clearance).

Dandelion seeds fall everywhere, but only take root where the soil suits them. Bone is a greenhouse for breast and prostate seeds because the seeds can trick the gardeners (osteoclasts) into digging up food for them.

A gated city with customs officers who throw out most goods (efflux pumps). Smugglers who get in bribe the local guards (astrocytes) to feed them. Drugs that work here are either small enough to slip past customs or arrive by a special convoy (focused ultrasound, intrathecal delivery).

Builders hired to repair a wall who never stop: they pour concrete around the tumour until the roads are blocked (vessels), the police cannot get in (T cells), and the very hardness of the concrete tells the tenants to multiply. Demolishing the builders' work made things worse; the newer plan is to retrain them.

A tumour that taps into the city's telephone lines: it receives growth orders from the nervous system, and brain tumours go further, plugging themselves into the switchboard so that ordinary brain chatter feeds them.