Cancer
Cancer is not one disease but a family of them — well over a hundred, united by a single broken rule. Every part of your body is built from cells that grow, divide and die on a tight schedule, taking their cues from the tissue around them. Cancer is what happens when a line of cells stops listening: it keeps dividing when it should stop, refuses to die when it should, and eventually spreads. This page is a plain-English tour of what that actually means — the biology underneath, how doctors describe and stage it, the main types, what raises the risk and what lowers it, how screening catches it early, the history of how we came to understand it, and the real and growing list of treatments. It is written to inform and to steady, not to frighten: cancer is common, much of it is preventable, a great deal of it is now treatable, and survival keeps improving. If you are worried about yourself or someone you love, the NHS cancer pages and Macmillan are good, calm places to start.
What cancer actually is
Start with the cell. An adult human is something like thirty trillion cells, and they are constantly being replaced — your gut lining renews in days, your skin in weeks. Each time a cell divides it must copy three billion letters of DNA, and copying is never perfect. Mistakes (mutations) creep in, and more arrive from sunlight, tobacco smoke, ordinary chemical wear and the simple passage of time. The body has elaborate machinery to spot and repair this damage, or to make a badly damaged cell quietly destroy itself. Cancer begins when, over years, a cell accumulates the particular handful of mutations that disable those safeguards.
The mutations that matter cluster in two kinds of gene. Oncogenes are the accelerators — genes that, when stuck “on”, tell a cell to keep dividing. Tumour-suppressor genes are the brakes — genes such as TP53 (often called the “guardian of the genome”) whose job is to halt division or trigger a damaged cell's self-destruction. Cancer is, in essence, a car with the accelerator jammed down and the brakes cut. It almost always takes several such changes, gathered one at a time, which is why cancer is overwhelmingly a disease of later life: it is the slow arithmetic of accumulated damage.
In 2000, two biologists, Douglas Hanahan and Robert Weinberg, distilled this sprawling disease into a famous shortlist they called the hallmarks of cancer — the capabilities a normal cell has to acquire to become a malignant one. They are worth knowing, because almost every treatment targets one of them:
- Sustaining proliferation — making its own “keep dividing” signals instead of waiting to be told.
- Evading growth suppressors — ignoring the brakes that tell normal cells to stop.
- Resisting cell death — dodging apoptosis, the orderly self-destruct programme that should eliminate a faulty cell.
- Inducing a blood supply (angiogenesis) — coaxing the body to grow new blood vessels to feed the tumour.
- Invasion and metastasis — breaking out of its home tissue and seeding elsewhere.
- Evading the immune system — hiding from, or switching off, the immune cells whose job is to find and destroy it.
Two more were added later — rewiring the cell's metabolism to fuel rapid growth, and the underlying genome instability and inflammation that generate the mutations in the first place. The point of the list is reassuring in its own way: cancer is not magic. It is a finite set of cellular tricks, and each one is a target we can learn to block.
Benign vs malignant, spread and staging
Not every lump is cancer. A benign tumour is an overgrowth that stays put — a mole, a fibroid, a lipoma. It can still cause trouble by pressing on something, but it does not invade neighbouring tissue or travel to distant parts of the body, and removing it usually ends the matter. A malignant tumour — what we mean by cancer — does two dangerous things a benign one does not: it invades the tissue around it, pushing fingers of itself through the normal boundaries, and it can metastasise, shedding cells that travel through the bloodstream or the lymphatic system and start new colonies elsewhere.
Metastasis is what makes cancer lethal. A tumour confined to its origin can very often be cut out or destroyed; once it has scattered seeds to the liver, lungs, bones or brain, it becomes far harder to clear. A metastasis keeps the identity of where it began — breast cancer that has spread to the lung is still breast cancer, and is treated as such, because its biology is set by its origin, not its new address.
To plan treatment and estimate outlook, doctors describe how far a cancer has gone using staging. The most common scheme is the TNM system: T for the size and extent of the primary tumour, N for whether it has reached nearby lymph nodes, and M for whether it has metastasised to distant sites. These combine into an overall stage from I to IV. Separately, grading looks down the microscope at how abnormal the cells appear: low-grade cells still resemble normal tissue and tend to grow slowly; high-grade cells look wild and disorganised and tend to behave more aggressively. Stage is about where the cancer has reached; grade is about how it is likely to behave.
| Stage | Roughly means | General outlook |
|---|---|---|
| Stage 0 | Abnormal cells confined to where they began (“in situ”); not yet invasive | Often curable by removal alone |
| Stage I | Small, localised; has not spread to nodes or beyond | Generally very treatable |
| Stage II | Larger, or just into immediately adjacent tissue; little or no nodal spread | Usually treatable, often curable |
| Stage III | More extensive locally and/or into nearby lymph nodes | Treatable; often needs combined therapies |
| Stage IV | Spread to distant organs (metastatic) | Usually treated to control and prolong; cure is harder but improving |
Exact definitions and what each stage means for outlook vary a great deal by cancer type — a stage IV testicular cancer and a stage IV pancreatic cancer are very different stories. Staging guides treatment; it is not a sentence.
The types and the common cancers
Cancers are named first by the kind of cell they start in, which is more informative than where in the body they sit. The broad families are:
- Carcinomas — by far the commonest, arising in the epithelial cells that line and cover the body's surfaces and organs. Breast, lung, prostate, bowel and most skin cancers are carcinomas.
- Sarcomas — arising in connective tissue: bone, muscle, fat, cartilage and blood vessels. Rarer, and a varied group.
- Leukaemias — cancers of the blood-forming cells in the bone marrow, which flood the blood with abnormal white cells rather than forming a solid lump.
- Lymphomas — cancers of the lymphatic system's immune cells, chiefly Hodgkin and the many non-Hodgkin lymphomas.
- Others — including melanoma (from the pigment cells of the skin), tumours of the brain and central nervous system, and germ-cell tumours such as most testicular and ovarian cancers.
A handful of cancers account for most of the burden. The table below sketches the common ones — what they affect and a note on each — though none of this replaces an assessment by a doctor.
| Cancer | Type | Notes |
|---|---|---|
| Breast | Carcinoma | The commonest cancer in women; mostly found through screening or a felt lump. Often treatable, especially when caught early; some are driven by hormones or the HER2 protein, which guides treatment. |
| Lung | Carcinoma | A leading cause of cancer death; strongly linked to smoking, though it occurs in non-smokers too. Often found late, which is why CT screening of higher-risk people is expanding. |
| Prostate | Carcinoma | Very common in older men; frequently slow-growing, so some cases are safely monitored rather than treated straight away (“active surveillance”). |
| Bowel (colorectal) | Carcinoma | Often develops from polyps over years, which is what makes screening so effective — polyps can be removed before they turn cancerous. |
| Skin | Carcinoma / melanoma | The commonest cancers of all. Most (basal and squamous cell) are very curable; melanoma is more serious but highly treatable when caught early. Sun and UV exposure is the chief driver. |
Causes and risk
The honest headline is that the single biggest risk factor for cancer is simply getting older. Cancer is largely a numbers game of accumulated DNA damage and bad luck in cell division — the longer you live and the more times your cells divide, the more chances there are for the wrong combination of mutations to land. This is why cancer has become more common as we live longer and conquer other causes of death; it is, in part, a by-product of success. None of which means it is purely random: a large slice of risk comes from causes we understand and can do something about.
The best-established carcinogens and risk factors include:
- Tobacco — the largest single preventable cause, behind lung cancer and many others (mouth, throat, bladder, pancreas).
- Alcohol — a Group 1 carcinogen, raising the risk of cancers of the mouth, throat, oesophagus, liver, bowel and breast. More on this in the guide to alcohol.
- Ultraviolet light from the sun and sunbeds — the main cause of skin cancers, including melanoma.
- Certain infections — some viruses and bacteria cause cancer over time: HPV (cervical and several other cancers, now largely preventable by vaccination), hepatitis B and C (liver cancer) and Helicobacter pylori (stomach cancer).
- Radiation — ionising radiation, and in homes the natural radioactive gas radon, raise risk; high doses are why radiology uses the lowest dose it can.
- Overweight and obesity — now one of the larger preventable causes, linked to bowel, breast, womb and several other cancers. See the guide to body weight.
- Occupational and environmental exposures — such as asbestos, certain industrial chemicals and air pollution.
- Inherited risk — a minority of cancers run in families. Faulty BRCA1 and BRCA2 genes, for instance, sharply raise breast and ovarian cancer risk, and Lynch syndrome raises bowel cancer risk. Genetic testing and extra screening can help those affected.
Cancer Research UK and others estimate that roughly 4 in 10 cancers in the UK are preventable through known risk factors — chiefly not smoking, keeping a healthy weight, drinking less alcohol, staying safe in the sun, and taking up vaccination (HPV) and screening when offered. That is not a promise — plenty of people who do everything right still get cancer, and it is never their fault — but at the level of whole populations, a large share of cancer is genuinely avoidable.
Screening and early detection
The single most useful fact about cancer treatment is that earlier-stage cancer is far more treatable than later-stage. A small, localised tumour can often be removed entirely; the same cancer found after it has spread is a much harder fight. Screening is the attempt to find cancers — or the changes that precede them — in people who feel perfectly well, before symptoms appear. The major national programmes are:
- Breast — mammography, an X-ray of the breast, offered to women in the relevant age range to catch tumours too small to feel.
- Cervical — cervical screening (the smear test), now usually testing for HPV first, finds pre-cancerous changes that can be treated long before cancer develops.
- Bowel — the FIT home test looks for tiny traces of blood in a stool sample, prompting a colonoscopy to find and remove polyps or early cancers.
- Lung — low-dose CT scanning is increasingly offered to people at higher risk (chiefly current and former smokers), where it catches lung cancers early enough to cure more of them.
Screening is one of medicine's great quiet successes — cervical screening and HPV vaccination together are on course to make cervical cancer rare. But it is not a free lunch, and being honest about that matters. Screening can throw up false alarms that lead to anxiety and further tests, and it can find slow, harmless growths that would never have caused trouble in a person's lifetime — over-diagnosis — leading to treatment that was not, in hindsight, needed. National programmes are designed around weighing these harms against the lives saved, and on balance the established programmes save many more than they harm. The practical advice is simple: take up the screening you are invited to, and ask your doctor about anything that does not feel right.
A short history
Cancer is ancient. It has been found in Egyptian mummies and even in dinosaur fossils — it is a deep consequence of being a multicellular animal whose cells divide. The earliest written description, the Egyptian Edwin Smith papyrus of around 1600 BCE, describes breast tumours and, against one, notes bluntly: “there is no treatment.”
The word itself comes from the Greek karkinos, meaning “crab”. Hippocrates is said to have chosen it because the swollen veins radiating from some tumours reminded him of a crab's legs; the Latin translation, cancer, gave us both the disease's name and the constellation. For well over a thousand years the dominant theory was Galen's — that cancer was caused by an excess of “black bile”, one of the four humours. It was wrong, but it held until the microscope and the modern understanding of the cell finally replaced it in the nineteenth century, when Rudolf Virchow established that cancers, like all tissue, are made of cells — cells gone wrong.
The first real weapon was the knife. As anaesthesia and antisepsis made surgery survivable in the 1800s, surgical removal became the mainstay, sometimes in radical, disfiguring forms. The second weapon arrived almost by accident: within a few years of Wilhelm Röntgen's discovery of X-rays in 1895 and the Curies' isolation of radium, doctors found that radiation could shrink tumours — the birth of radiotherapy. The third came out of war: soldiers exposed to mustard gas in the World Wars were found to have depleted white blood cells, which led, in the 1940s, to using related chemicals to attack leukaemia — the first chemotherapy.
In 1971 the United States declared a “War on Cancer”, pouring money into research. Progress was slower than promised, but the science deepened: the 1970s and 80s revealed oncogenes and tumour-suppressor genes, recasting cancer as fundamentally a disease of genes. Alfred Knudson's “two-hit” hypothesis explained why some cancers run in families — you can inherit one faulty copy of a suppressor gene and need only a second hit to lose the brake entirely. That genetic understanding eventually paid off in treatment: Herceptin (trastuzumab), approved in 1998, was an antibody aimed precisely at the HER2 protein that drives a subset of breast cancers — the dawn of targeted therapy. Most recently, drugs that release the brakes the immune system puts on itself — immune-checkpoint inhibitors — transformed the outlook for melanoma and other cancers, earning James Allison and Tasuku Honjo the 2018 Nobel Prize in Medicine.
Treatment
There is no single treatment for cancer, because there is no single cancer. Modern care draws on a growing toolkit, usually combining several approaches, and almost always planned by a multidisciplinary team — surgeons, oncologists, radiologists, pathologists, specialist nurses and others meeting together to tailor a plan to the individual tumour and person. The main modalities are:
| Modality | What it does |
|---|---|
| Surgery | Physically removes the tumour and, often, nearby lymph nodes. The oldest and still the most likely to cure a localised cancer outright. |
| Radiotherapy | Uses focused high-energy radiation to damage cancer cells' DNA so they cannot keep dividing. Increasingly precise, sparing surrounding tissue. |
| Chemotherapy | Drugs that kill rapidly dividing cells throughout the body — powerful against cancer, but also the cause of familiar side effects, because it hits some healthy fast-dividing cells too. |
| Hormone therapy | For cancers fuelled by hormones (many breast and prostate cancers), blocks or lowers those hormones to starve the cancer. |
| Targeted therapy | Drugs aimed at a specific molecule a particular cancer depends on (such as HER2, or a mutated growth signal), often with fewer broad side effects. |
| Immunotherapy | Helps the patient's own immune system find and destroy cancer — chiefly checkpoint inhibitors, and CAR-T therapy, where a patient's own T-cells are re-engineered to hunt their cancer. |
| Stem-cell / bone-marrow transplant | Replaces blood-forming cells after very high-dose treatment, used mainly for leukaemias and lymphomas. |
Treatment is given with one of two intentions, and being clear about which matters. Curative (or radical) treatment aims to remove or destroy the cancer completely. Palliative treatment aims to control the cancer, relieve symptoms and extend good-quality life when cure is not realistic — and it can do that for a long time. It is important to understand that palliative is not a synonym for “giving up”; it is active, skilled care focused on living as well as possible.
The side effects are real and deserve to be named honestly rather than minimised — fatigue, nausea, hair loss with some chemotherapy, lowered immunity, and others that depend on the treatment. They are usually manageable, often temporary, and the team's job includes treating them, not just the cancer. Anyone going through treatment should feel able to report side effects: there is almost always something that can help.
Living with cancer and prognosis
The picture is, genuinely, far brighter than the word “cancer” often makes people fear. Across the rich world, cancer survival has improved markedly over the past half-century — for many cancers it has roughly doubled. Testicular cancer and many childhood cancers are now usually cured; most breast, prostate and skin cancers caught early do very well. Even advanced cancers that cannot be cured can increasingly be held in check for years, lived with rather than simply died of.
That has created a large and growing population of survivors, and a field — survivorship — devoted to life after and alongside treatment: managing long-term side effects, the fear of recurrence, fertility, work, and the ordinary business of getting on with living. Survival statistics are population averages, not individual predictions; they describe groups, and no statistic knows your particular case.
And when a cancer cannot be cured, palliative and hospice care comes into its own. It is one of the most misunderstood parts of medicine. Far from being about “giving up”, it is a specialism in living as fully and comfortably as possible — controlling pain and other symptoms, supporting families, and honouring what matters most to a person. Studies have even found that good early palliative care can improve quality of life and, in some cases, length of it. Organisations like Macmillan exist precisely to support people and families through all of this.
What the research says & frontiers
Cancer research is moving fast, and the direction of travel is towards treatments matched ever more precisely to the individual tumour. A few of the most promising frontiers:
- Precision oncology — reading the genetic profile of a particular tumour to choose the drug most likely to work against it, rather than treating by organ alone. The same drug may treat cancers from different organs that share a mutation.
- Liquid biopsies — blood tests that detect tiny fragments of tumour DNA, with the promise of catching cancer earlier, tracking whether treatment is working, and spotting recurrence sooner than scans can.
- mRNA cancer vaccines — using the same technology behind recent vaccines to train the immune system against a patient's own tumour markers; early trials, including in melanoma, are encouraging.
- Expanding cell therapies — extending CAR-T and related approaches, already transformative in some blood cancers, towards the harder problem of solid tumours.
- AI in pathology and imaging — machine-learning tools that help spot tumours on scans and slides earlier and more consistently, as a second pair of eyes for specialists.
None of these is a single “cure for cancer” — that framing was always a misunderstanding of a hundred-odd different diseases. But taken together they are steadily turning more cancers into conditions that can be caught early, treated precisely, and either cured or lived with.
Where to get help & more info
If you have noticed a possible symptom — a new or changing lump, unexplained bleeding, a mole that has changed, unexplained weight loss, a persistent cough or a change in bowel habits — the right move is simple: see your GP. Most such symptoms turn out not to be cancer, but checking early is always worthwhile, and you will never be wasting anyone's time.
Trustworthy, free sources of information and support:
- NHS — Cancer: symptoms, types, screening and what to expect (UK).
- Macmillan Cancer Support: practical, emotional and financial support, plus a free helpline.
- Cancer Research UK: clear explainers on every cancer type, causes and prevention.
- WHO — Cancer fact sheet: the global picture, causes and prevention.
- American Cancer Society and the US National Cancer Institute: thorough reference material.
- CDC: prevention and screening guidance.
Related guides on this site: alcohol, a Group 1 carcinogen, and body weight, now one of the larger preventable risk factors.
Some of the figures and details on this page — typical ranges, statistics and the biology — were compiled with the help of AI tools and may contain errors or be out of date. They are shared in good faith for general interest only, and are not medical advice. Nothing here is a substitute for a doctor or a qualified health professional; if you are worried about cancer, please seek professional help. Check claims against primary medical sources before relying on them.