What is cancer?

Expert reviewers, Professor Andrew Protheroe, Consultant Oncologist and Jo Byfleet, Bupa Clinics GP and Physician in Charge
Next review due January 2024

Cancer is when abnormal cells in your body grow in an uncontrolled way. It is the name given to a group of over 200 related diseases which can start almost anywhere in the body.

Half of us will get cancer at some point – mostly in old age. Although it can be serious, many people are cured and more than half live for over 10 years. Research is going on all the time to improve diagnosis and treatment.

Below is some very general information about cancer. You will find links to our other cancer information and other helpful organisations.

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About cancer

Your body is made up of many different types of cells that form your tissues and organs. Body tissues grow by individual cells dividing into identical ‘daughter cells’. This normally happens in a controlled way for growth and repair. But cancer cells don’t stop dividing when they should. Often, they form lumps called tumours. Blood cancers such as leukaemia don’t form tumours but the abnormal cells build up in the blood.

Cancer cells can spread into surrounding tissues or to other parts of the body. This is called metastasising. Your doctor may call cancer that has spread a ‘secondary tumour’ or ‘metastatic cancer’.

Symptoms of cancer

Cancer symptoms vary depending on the type of cancer, but there are certain symptoms to look out for. These include the following.

  • A new lump in any area of your body – for example, a breast lump or testicular lump.
  • Unusual bleeding – for example, in pee, vomit or poo (stool).
  • Coughing up blood or a cough that won’t go away.
  • A sore that won’t heal anywhere on the body.
  • Unexplained weight loss.
  • Unexplained reduced appetite.
  • Feeling bloated most days.
  • Changes to a mole – for example, bleeding, itching or a change in size or colour.
  • Change in bowel habits – for example, constipation or diarrhoea for more than three weeks.
  • Difficulty peeing (for men).
  • Having indigestion often or difficulty swallowing.
  • Unexplained vaginal bleeding – for example, between periods, after sex or after menopause.

These symptoms are often caused by other medical conditions that aren’t cancer. But if you have any of them or notice other unusual changes in your body which don’t go away, contact your GP.

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Cancer screening

Cancer screening involves testing seemingly healthy people for cancer. There is then the option for further tests which may show if you have the cancer or not. Approved screening tests can save lives and improve quality of life. This is because they can diagnose cancer early. Screening tests can reduce the chance of developing a serious condition.

However, it’s important to understand that screening tests aren’t always accurate. There is the possibility of a false negative (an incorrect negative result) or a false positive (an incorrect positive result). It is also important to remember that a genuinely negative result doesn’t mean you won’t get cancer in the future.

So far, there are screening tests for cancer of the cervix, breast cancer and bowel cancer. At the moment for the general population, there are no reliable screening tests for other cancer types. However, research is going on all the time. Some screening tests are offered to people who are known to be at higher risk of some cancers. For example, those who have inherited certain genes that increase their risk.

When you are invited to have screening depends on your age and gender. Accepting or refusing a screening test invitation is a personal choice. Talk to your GP if you have any questions about cancer screening.

Diagnosis of cancer

If you have symptoms, your GP will ask about these and may examine you. They may ask about your medical history and cancer in members of your family. You may need tests to see if your symptoms are caused by cancer or another condition. Tests may include:

Your GP may refer you to a specialist. You’ll usually see them within two weeks if cancer is suspected. Other tests depend on your symptoms and the area of your body affected. For example, you may have an examination using a tube to look inside your stomach or bowel (an endoscopy).

You may also need a biopsy. This is a small sample of tissue which is removed and sent to a laboratory to check for cancer cells.

If you have cancer, you may need other tests to see how big the cancer is and if it has spread. This is called staging. Staging is important because it helps your doctor decide on the best treatment for you.

If your doctor recommends any tests, they’ll explain why the test important and what is involved. It’s OK to ask questions and raise any concerns you have.

Treatment of cancer

Different types of cancer respond to different treatments. Your treatment also depends on how much the cancer has grown and if it has spread. You may have treatment to:

  • cure the cancer
  • shrink or slow down the cancer growth to prolong your life
  • reduce the symptoms caused by the cancer – this is called palliative therapy

You may have surgery to remove the cancer. You may have chemotherapy and radiotherapy before or after surgery or on their own. Other treatments include immunotherapy (using your immune system to fight cancer), hormone therapy and treatments that directly target cancer cells (called targeted or biological therapies). Some cancers are treated with high-dose chemotherapy followed by a stem cell transplant.

Your doctor will discuss treatment with you and go through any possible choices. They may also ask if you’d like to take part in a clinical trial to help improve existing treatment or test a new treatment. It is OK and important to ask questions as you go through the process.

Who’s who in cancer

You may come across many different doctors and healthcare professionals during cancer care. They each have different expertise and together can provide the best treatment for you.

  • Cancer nurse specialist – a healthcare professional who has in-depth knowledge in cancer care and is your main point of contact during and after treatment.
  • Oncologist – a doctor with specialist knowledge of chemotherapy, radiotherapy, immunotherapy and other non-surgical cancer treatments.
  • Surgeon – in cancer, different surgeons specialise in operating on specific parts of the body.
  • Radiographer – a technician trained in using techniques such as X-ray, MRI and CT scans to take images. They are also trained to operate the machines that deliver radiotherapy.
  • Radiologist – a doctor who specialises in using scans and X-rays to diagnose medical conditions, including cancer.
  • Dietitian – a healthcare professional who can advise on healthy eating and what to do if you’re having trouble eating and drinking because of your cancer treatment.
  • Physiotherapist – a healthcare professional who specialises in maintaining and improving movement and mobility.
  • Psychologist – a healthcare professional who specialises in helping with emotional and behavioural problems.
  • Counsellor – a professional who provides emotional support.
  • Pharmacist – a professional who prepares and checks medicine prescriptions and can advise on how to take medicines and on side-effects.
  • Occupational therapist – a professional who provides practical assistance to help you manage everyday activities and increase your independence.

Types of cancer

Cancers are named after the types of cells they develop from. We describe the three main groups here, but there are many other types.


Overall, 85 out of every 100 cancers are carcinomas. These start off in epithelial cells, which cover surfaces and line organs and tissues. Common types include cancers of the breast, lung, prostate and bowel. Together, these four cancers make up over half of all new cancers diagnosed.


Fewer than one in 100 cancers are sarcomas. These develop from the cells of connective tissues, which includes bone, muscle and blood vessels. The two main types are bone sarcomas and soft tissue sarcomas.

Cancers of blood cells

These include cancers of your blood and lymphatic system – lymphomas, leukaemias and myeloma.

  • In leukaemia, your bone marrow makes too many white blood cells which are abnormal and don’t work properly.
  • Lymphomas are cancers starting in your lymphatic system. This is a network of tubes and glands (lymph nodes) that help to fight infection and filter the blood.
  • Myelomas are cancers of blood cells called plasma cells.

Only about nine in every 100 people diagnosed with cancer have leukaemia, myeloma or lymphoma. But although they’re quite rare, leukaemias are the most common cancers in children.

Causes of cancer

Cancer isn’t infectious and you can’t catch it from other people. Around four out of 10 cancers are preventable. So you can reduce your risk by making healthy lifestyle changes.

Most cancers are caused by a combination of factors. Age is the biggest single risk factor – half of newly diagnosed cancers are in people aged 70 or over. Other causes include the following.

  • Smoking – this is the main cause of lung cancer. It also increases the risk of many other cancers, including cancers of the bladder, kidney, stomach and oesophagus.
  • Family history – some cancers run in families because you can inherit genes that increase risk of specific types of cancer, including breast, bowel, ovarian and prostate cancers. Speak to your GP if you’re concerned about cancers in your family. They will be able to assess if you would benefit from a genetics referral to consider your risk further.
  • Food and drink – a diet that is high in animal fats and red and processed meat but low in fruit and vegetables increases risk for some types of cancer. Drinking too much alcohol and being overweight can also increase risk.
  • Lack of exercise – not being physically active increases the risk of some cancers including breast and bowel cancer.
  • Sun and sunbeds – ultraviolet (UV) rays increase the risk of skin cancer, including melanoma.
  • Infections – for example, infection with a virus called human papilloma virus (HPV) increases risk for cervical, mouth and genital cancers.
  • Cancer-causing substances (carcinogens) – some substances are known to cause cancer, examples include asbestos and radioactive materials.

Help and support

Being diagnosed with cancer can be distressing for you and your family. You may need support to deal with the emotional aspects as well as physical symptoms. Specialist cancer doctors and nurses are experts in providing the support you need. Talk to your doctor or nurse if you’re finding your feelings hard to cope with.

Everyone has their own way of coping. But for further support and advice, you may find it helpful to contact one of the organisations in our helpful websites section. They have information about most types of cancer in more detail than we can go into here. Some have a telephone helpline or an online forum you can join. Your cancer team may be able to direct you to local support groups where you can meet other people with similar medical issues. There are also support groups for carers.

We have much more detailed information about many different types of cancer on our website.

Frequently asked questions

  • The most common cancer in the UK is breast cancer, followed by lung, prostate and bowel cancer. Over half of all people who are newly diagnosed with cancer have one of these types.

    Out of every 100 women who have cancer: 

    For every 100 men who have cancer:

    • 26 have prostate cancer
    • 13 have lung cancer
    • 13 have bowel cancer
    • 48 have other cancers (including cancer of the head and neck, cancer of the kidney and melanoma)

  • It can be very upsetting if someone you know has cancer, but there are lots of things you can do to help.

    Talking to your friend will help you to understand how they’re feeling and coping with the illness. Be realistic about how much time you can spend with them. Try to be reliable, so they know how much they can depend on you.

    You may find it hard to talk to your friend at first. If they don’t feel ready to talk, carry on with life as usual but offer your support. Find out information about their cancer type to help you understand what they’re going through. But don’t try telling them about it. It can be different for different people and they will get the most reliable information from their own medical team. This is a time when you can do most good by listening.

    Respect your friend’s privacy if they don’t want to talk about their cancer to you or to other people. Just being there and continuing to stay in touch can be a support. Many people like to try and keep their lives as normal as possible when they’re having treatment for cancer.

    Try to think about specific practical ways you can help rather than just asking if there’s anything you can do. Perhaps offer to cook a meal, pick up the children from school or do some shopping. You could also offer to take your friend to medical appointments or treatment sessions. Be sensitive if your friend doesn’t want support. Let them know the offer is still available if things change later.

    Remember to take time out for yourself because supporting somebody with cancer can be stressful and upsetting. Talk to other people about how you’re feeling and make sure others are involved with caring too. There are many support groups that offer help and advice for friends and family of people with cancer – see our section on other helpful websites.

  • Cancer can be cured in many cases, but not always. Whether or not you can be cured depends on a number of things. These include the type of cancer you have, how far the cancer has grown or spread, and your age and general health. Everyone is different. Your doctor will be able to talk to you about the chances of a cure in your particular circumstances.

    Different cancers respond to different treatments so there won’t ever be a single cure for cancer. There are over 200 different types of cancer and some are easier to cure than others. For most cancers, the earlier you’re diagnosed, the better the chance of cure. So contact your GP as soon as possible if you have a symptom you’re worried about.

    If your cancer can’t be cured, there are usually treatments which will slow it down or control it. These can give you many extra months or years of good-quality life as well as relieve your symptoms.

    You may hear your doctor say your cancer is ‘in remission’ rather than cured. Remission means that there are no signs of cancer in your body, but your doctor can’t say for sure that it will never come back. Some cancers can recur many years after they seem to have gone. But in general, the more time that has passed, the lower the chance of the cancer coming back.

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Related information

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  • Reviewed by Liz Woolf, Freelance Health Editor and Natalie Heaton, Specialist Health Editor, Bupa Health Content Team, January 2021
    Expert reviewers, Professor Andrew Protheroe, Consultant Oncologist and Jo Byfleet, Bupa Clinics GP and Physician in Charge
    Next review due January 2024