Cancer Explained
Informed by recognized medical guidance
Overview
Cancer is a group of diseases where some cells in the body grow out of control and spread into other tissues. Normally, cells grow, divide, and die in an orderly way. In cancer, this process breaks down. These abnormal cells can form a lump called a tumor, or they can travel through the blood or lymph system to other parts of the body. There are many types of cancer, and each behaves differently.
Key facts
- Cancer is not one disease — it is many diseases with different causes, treatments, and outcomes.
- Not all lumps are cancer, and not all cancers form a lump.
- Some cancers can be cured, and many can be treated effectively for years.
- Early detection often gives more treatment options and better chances.
- A cancer diagnosis does not mean a death sentence — many people live long, full lives after treatment.
Yes, cancer is very common. About 1 in 2 people in the UK will develop some form of cancer during their lifetime. It can happen at any age, but it becomes more common as people get older.
Anyone can get cancer. It affects people of all ages, genders, and backgrounds. Some people have a higher risk because of their family history, lifestyle, or certain infections. Children can get cancer too, but it is rare. Most cases are in adults over 65.
Symptoms
- Sudden severe shortness of breath
- Coughing up blood in large amounts
- Sudden severe headache or seizure
- Weakness or numbness on one side of the body or trouble speaking (signs of stroke)
- New confusion or inability to wake up
- Sudden severe abdominal pain that does not go away
- ⚠Abnormal bleeding (such as blood in vomit, stool, urine, or from any opening)
- ⚠A lump that is growing quickly or changing
- ⚠High fever that does not improve
- ⚠Significant unexplained weight loss over a few weeks
- ⚠A painful area that is getting worse
- ⚠Difficulty swallowing or breathing when not severe
Common symptoms
- A new lump or swelling anywhere in the body
- Unexplained weight loss (losing weight without trying)
- Persistent tiredness or fatigue that does not improve with rest
- Changes in a mole or skin lesion
- Persistent cough or hoarseness that lasts more than 3 weeks
- Changes in bowel or bladder habits (such as blood in stool or urine, or lasting constipation or diarrhea)
- Difficulty swallowing
- Unusual bleeding or discharge (for example, blood from the rectum or between periods)
- A sore that does not heal after more than 4 weeks
Symptoms in children
- Persistent or unexplained fever
- Pale skin or easy bruising
- Frequent infections
- Bone pain or limping for no clear reason
- A noticeable lump, especially in the belly, neck, or arms
- Sudden changes in vision or eye appearance
- Unexplained weight loss or poor appetite
Symptoms in older adults
- Any of the common symptoms, but they may be subtler or mistaken for aging
- New or unusual pain that does not go away
- Unplanned weight loss
- Extreme tiredness or weakness
- A change in skin colour or a new skin growth
- Blood in the stool or urine (sometimes not visible — found in tests)
- Difficulty passing urine or a weak stream
Causes
Main causes
- Cancer starts from changes (mutations) in the DNA of normal cells. These changes can happen by chance, due to inherited genes, or from exposure to certain substances.
- Tobacco smoke is the biggest cause of cancer that can be prevented.
- Ultraviolet (UV) radiation from the sun or tanning beds can damage skin cells and cause skin cancer.
- Some infections can raise cancer risk, such as certain types of HPV (human papillomavirus) for cervical and other cancers, or hepatitis B or C for liver cancer.
- Chronic inflammation or long-term reflux can increase risk in some tissues.
- Hormones can affect the growth of some cancers, such as breast and prostate cancer.
Risk factors
- Getting older
- Smoking or using tobacco in any form
- Drinking alcohol regularly or in high amounts
- Being overweight or obese
- Lack of physical activity
- Unhealthy diet low in fruits and vegetables and high in processed meats
- Excess sun exposure or sunbed use
- Family history of certain cancers
- Exposure to certain chemicals (like asbestos or benzene) at work
- Certain viral infections (HPV, hepatitis B or C, HIV)
- Previous radiation therapy
When to see a doctor
See a doctor urgently if:
- If you notice any of the common warning signs that last more than 3 weeks — for example, a persistent cough, a lump, unexplained weight loss, or unusual bleeding — see your GP.
- If you have symptoms that are unusual for you, don't wait — make an appointment.
- If you feel something is seriously wrong with your body, trust yourself and see a doctor.
Book a routine appointment if:
- If you have any mild symptom that worries you but is not urgent, speak to your doctor during a routine appointment.
- If you are due for a cancer screening test (such as bowel, breast, or cervical screening), do not miss it — talk to your GP if you haven't received an invitation.
Diagnosis
To diagnose cancer, a doctor will talk to you about your symptoms, examine you, and usually order some tests. If you have a lump or unusual symptoms, your doctor may need to take a small sample of tissue (biopsy) to check for cancer cells. You may also have imaging scans such as an ultrasound, CT or MRI to see inside your body.
Tests that may be done
- Blood tests
- Urine tests
- Imaging scans: ultrasound, X-ray, CT, MRI, or PET
- Biopsy (taking a small piece of tissue)
- Endoscopy (a thin tube with a camera to look inside your body)
- Procedures like colonoscopy or cystoscopy for specific areas
What to expect at your appointment
If cancer is found, your doctor will explain what type it is and how far it has spread (the stage). You will be referred to a specialist team. They will discuss treatment options with you. You may have more tests to plan the best care. It is normal to feel anxious, but your healthcare team will guide you step by step.
Treatment
There are many ways to treat cancer. The right treatment depends on the type of cancer, where it is, whether it has spread, and your general health. You will have a team of specialists who work with you to decide the best plan. Treatments aim to remove or destroy cancer cells, control their growth, and relieve symptoms.
Self-care at home
- Follow your doctor's advice and attend all appointments
- Get plenty of rest and listen to your body
- Ask for help from family and friends when you need it
- Keep a record of your symptoms and questions for your doctor
- Use gentle exercise if you feel up to it, like short walks
- Eat as well as you can, even if small meals more often
- Talk to someone about your fears — you don't have to face it alone
Medical treatments
Treatment may include surgery to remove the cancer, chemotherapy (drugs that kill or stop cancer cells), radiotherapy (high-energy rays to shrink tumors), targeted therapy (drugs that aim at specific changes in cancer cells), immunotherapy (helping your immune system fight cancer), or hormone therapy (blocking hormones that help some cancers grow). You may receive one or a combination of these. New treatments and clinical trials can also be options. Your doctor will explain what is available for your situation.
When is surgery considered?
Surgery may be offered if the cancer is in one place and can be removed safely. Sometimes surgery is done to take out the whole tumor, or to remove nearby lymph nodes to see if the cancer has spread. For some early cancers, surgery alone might be enough. In other cases, surgery is combined with treatments before or after.
Living with this condition
Living with cancer can be challenging. You may have good days and bad days. It helps to set realistic goals, keep a routine, and accept support. You may feel tired during treatment, so plan rest times. You can still do things you enjoy when you have energy. Let your healthcare team know about any side effects or pain — there are many ways to help.
Lifestyle tips
- Stop smoking if you smoke — it can improve treatment outcomes and overall health
- Limit alcohol or avoid it completely
- Stay as active as you can with gentle activities approved by your doctor
- Protect your skin from the sun and avoid sunbeds
- Try stress-reducing activities like breathing exercises, meditation, or talking with a friend
Diet and exercise
Eat a balanced diet with plenty of fruits, vegetables, whole grains, and lean proteins. If food is hard to keep down, eat small, frequent meals. Stay hydrated. Walking, stretching, or light swimming can help maintain strength and mood — but check with your care team before starting new exercises.
Mental health and emotional wellbeing
A cancer diagnosis can bring anxiety, fear, anger, and sadness. These feelings are normal. Many people also feel depressed or overwhelmed. It is important to talk to your doctor or nurse about how you feel. They can put you in touch with counseling or support groups. You don't have to be brave all the time. Reaching out is a sign of strength.
Prevention
Not all cancers can be prevented, but up to half of all cancers could be prevented by changes in lifestyle. Not smoking, keeping a healthy weight, being active, eating well, limiting alcohol, and protecting your skin from sun all reduce your risk. It is also important to get vaccinated against infections that can cause cancer and to take part in screening programs.
Vaccines
Vaccines can protect against certain infections that cause cancer. The HPV vaccine protects against human papillomavirus, which causes most cervical cancer and some other cancers. The hepatitis B vaccine can reduce the risk of liver cancer. Ask your doctor about your vaccination status.
Screening programmes
Screening tests can find early changes that may lead to cancer, or catch cancer before symptoms appear. Examples include bowel cancer screening, breast cancer screening (mammography), and cervical screening (smear test). These are offered nationally in many countries, including the UK. If you get invited, it is important to go. Talk to your doctor about which tests are right for you.
Complications
If left untreated
- Cancer can grow and spread to nearby tissues or other organs, which may make treatment harder.
- It can block important pathways (like the bowel or windpipe) and cause dangerous emergencies.
- It can cause severe pain, weight loss, and fatigue.
- Some cancers can affect the immune system, making serious infections more likely.
- Untreated cancer can become more difficult to control and may become life-threatening.
Long-term outlook
It is natural to worry about the future, but there is great hope. Many cancers are cured, and for others, treatment can control the disease for many years. Research is constantly improving treatments and survival rates. Even with an advanced cancer, modern care can help people live well and comfortable. Every person's situation is unique — your medical team will give you a realistic picture and support you at every step.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: August 2, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.
Guidance may differ by country or region. Confirm local recommendations with a qualified healthcare provider.