Cancer cells can interfere with or damage organs. Most dangerously, they sometimes gain the ability to move to entirely new places in the body, spreading their damage to multiple tissues and organs. 

Cancer in the UK

About one in every two people in the UK get cancer at some point in their lives, with the risk being higher as they get older. Many cancers can be treated very effectively, especially if caught early on. But there are a wide variety of cancer types and others that are more difficult to manage.

We have better treatments than ever before but cancer still causes about one in every four deaths in the UK. For this reason it is a very important area of research.

Research looking at the causes of cancer have found that there are many things we can do (or not do) to reduce our personal risk of developing cancer. There are also changes we can make as a society; for example, changes in smoking laws led to a fall in the rate of lung cancer.

What is Cancer?

Cancer happens when cells develop new behaviours.

We don’t have the same cells all through our lives. Cells divide to make more cells so that we can grow.

New cells are also needed to replace old cells. Most cells last about seven to ten years before they need to be replaced, although life spans vary a lot. Some blood cells can last less than a day, while other cells last a lifetime.

Normally there are strict controls on how cells divide and grow. But sometimes a cell changes so that it divides and grows more than it should. The extra cells it produces are just like itself, meaning that they also divide and grow more than they should.

Often, this isn’t a cause for alarm. The cells stay where they are, slowly dividing to create a small lump of extra cells known as a tumour. This type of tumour is not cancerous; it is a benign tumour. Benign tumours are usually harmless, although occasionally they might cause problems by pushing against nearby tissues or producing substances. Benign tumours have obvious edges so it’s usually relatively simple to remove them by surgery if necessary.

But sometimes the cancer cells start spreading out. The cancer cells might invade nearby tissues or even break off to travel in the blood, reaching other organs of the body. This can spread damage to multiple organs and tissues, causing serious problems. Tumours that spread like this are called malignant tumours. Cells in malignant tumours usually grow and divide more quickly than those in benign tumours.

You may have heard of cancers being referred to by stages – for instance “Stage 4 cancer”. This is a way to categorise them based on how they have spread in the body. Stage 1 cancers are small and found in one single lump, while Stage 4 cancers have already spread to another organ. Stage 2 and 3 cancers are in-between stages. 

Types of Cancer

Every cancer is different. The cancer cells are unique to that person, and the way the cells move around the body can be very different too. This means people’s experiences can vary a lot, even if they have the ‘same’ type of cancer.

That said, knowing what type of cell the cancer came from can give important clues as to how it will behave and respond to treatment. For this reason it’s really important to work where the cancer started. This isn’t always obvious because a cancer might be discovered in one place, but have travelled there from somewhere else.

There are certain cell types that are more likely than others to become cancerous. The most common cancers in the UK are breast, prostate, lung, and bowel cancers.

Through awareness campaigns, ordinary people can learn how to spot the early symptoms of common cancers, and how to check themselves for unusual lumps. There are also screening programmes for the people who are most at risk, where they have scans or other checks. This is really important because the earlier a cancer is discovered, the easier it will be to treat.  

Endocrine Cancers

Endocrine cancers are rare cancers that start in hormone-producing tissues, usually within glands. 
Sometimes the cancer comes from the cells that makes the hormones - this can lead to increases in the amount of hormone in the body. Or sometimes cancer from nearby cells causes damage that reduces the amount of hormone that is released. These changes in hormone levels can have widespread effects on other organs throughout the body.

The most common endocrine cancer is thyroid cancer.

Thyroid Cancer

About one in every hundred cancers in the UK is thyroid cancer. The good news is there are effective treatments for this cancer. Most people with thyroid cancer make a full recovery.  

The thyroid gland is a butterfly-shaped organ wrapped around the windpipe, in the front of the neck. It produces and releases thyroxine and other hormones. These hormones are used as signals to help control the body’s metabolism, growth and development.

Thyroxine is an important hormone that regulates many processes in the body, including metabolic rate, heart, digestive function, muscle control, brain development and maintenance of bones.

If thyroxine-producing cells grow into a benign tumour (a tumour that stays in place), this can lead to the release of too much thyroxine. Because thyroxine has such widespread effects in the body, this causes a wide variety of symptoms. The most common symptoms are weight loss, fast (and sometimes irregular) heart rate, irritability or nervousness, muscle weakness and tremors (regular quivering), changes in menstrual periods, sleep problems, eye problems, and heat sensitivity.

Much more rarely, a malignant tumour (cancer) can develop. Treatment can include removal of the thyroid gland if necessary. If this is done, the person will need to take hormones to replace the ones that their thyroid would normally be making. They need to do this for the rest of their lives.  

Pancreatic Cancer

The pancreas is a gland near the stomach. It produces both digestive juices and a variety of important hormones.

The hormones produced by the pancreas include insulin and glucagon, which are both extremely important in controlling the amount of glucose (sugar) in the blood and tissues. Glucose is a vital source of energy for our cells. You can find out more about how the pancreas uses its hormones to control blood glucose levels in our articles The Pancreas and Sugar Control in the Body.

Most pancreatic cancers start from a cell in the duct that carries the digestive juices. These cancers may also spread to damage the part of the pancreas that produces hormones. Sometimes the whole pancreas has to be removed. This leads to a condition called Type 3c diabetes. This rare version of diabetes mellitus is different from the much more common Type 1 and Type 2 diabetes because it affects all the pancreatic sugar-control hormones, not just insulin.

It is also possible (but very rare) for cancers to form from the pancreatic cells that produce hormones. These endocrine cancers can lead to over-production of a single hormone, again throwing the sugar-control system out of balance. The effects and treatments will depend on which type of hormone is being made. 
If the pancreas is damaged or removed due to cancer, long-term treatments can include insulin injections, hormone tablets, and tablets containing digestive enzymes to replace those the pancreas is no longer able to provide.

Pancreatic cancer is often discovered late, when it is more difficult to treat. People who are known to have a high genetic risk for this cancer can have regular checks to try to catch it early if it does develop. 

Causes of Cancer

Cancer rarely has one single cause. It is much more often due to a mix of different factors. These factors add up to increase the risk of cancer over a person’s lifetime, which is why most cancers are more common in elderly people.

Risk factors include having particular genes (that you inherited from your parents), having particular gene mutations (that happened during your lifetime), exposure to cancer-causing chemicals or radiation, and infection with certain viruses.

Living a healthy life with a balanced diet and exercise can help reduce your risk of many cancers. However it’s not possible to avoid the risk entirely. Being alert for unusual lumps is important for everyone. Other recommended checks include blood tests for prostate cancer for older men. 

Inherited genes (genetics)

People with genes that carry a high risk for cancer often already know that a particular cancer is very common in their family. It is possible to check whether an individual has inherited such genes. For example, some genes carry a very high risk of breast cancer (e.g. BRCA1 and 2). People who find out that they carry these genes may choose to have extra checks, or even a mastectomy (breast removal) to avoid the risk of any cancer developing.

Other genes might just give a slightly higher or lower risk of particular cancers. But it’s very difficult to calculate these risks because there are so many other factors that affect an individual’s chances of getting cancer.

Gene mutations

Gene mutations happen when DNA is mis-copied during the process of making a new cell, or through DNA damage. Cells have systems to check the DNA and fix mistakes, but with trillions of cells in your body it’s impossible for the DNA to be copied perfectly every single time.

Often these mutations don’t matter, but just occasionally they might increase the risk of cancer. The more times cells divide, the more likely such mutations are to happen. This means that older people are more likely to carry such mutations.

It’s impossible to avoid gene mutations completely. However, we can reduce the risk of gene mutations by avoiding exposure to certain chemicals and radiation.

Chemicals

Some chemicals and radiation can damage our DNA, directly causing gene mutations. Substances that cause cancer like this are called carcinogens.

The most well-known carcinogen is probably cigarette smoke, which can cause lung cancer when inhaled. Alcohol is another common carcinogen. It can cause cancer because it is broken down in the body to form a carcinogenic molecule called acetaldehyde.

There are laws to control exposure to the most dangerous carcinogens, including chemicals used in industry. But it is impossible to avoid carcinogens entirely; we encounter many examples in our everyday lives, including in our diet.

The common lifestyle factors that most increase cancer risk is how much a person smokes or drinks alcohol, and if they eat a lot of red meat or processed meats.

Radiation

The most dangerous radiation is ionising radiation. Ionising radiation is high-energy radiation with the power to ionise molecules. People might be exposed to it through X-rays, or by living in a home exposed to radioactive radon gas. This radiation can directly damage DNA, causing cancers. This is the reason why the X-ray technician leaves the room during the scan – having a few X-rays for medical reasons is very low risk, but being exposed many times a day for a whole working life could be dangerous.

The ability of ionising radiation to damage cells can also be used for positive purposes. In radiotherapy, doctors use carefully focused radiation to damage and destroy cancer cells.

Ultra-violet light is lower energy than ionising radiation, but still has enough energy that it can cause damage. Exposure to sunlight can increase the risk of skin cancers. Using protective sun creams and wearing hats are simple ways to reduce this risk.

Viruses

Some viruses can increase the risk of cancer.

The sexually-transmitted virus Human papillomavirus (HPV) has been shown to cause cancers including cervical cancer and anal cancer. Not everybody with the virus will get cancer, but it greatly increases the risk.

A vaccine for HPV is now offered to children when they are 12-13 years old. This has hugely reduced the number of people getting cervical cancer – a great public health success! However, screening is still important to catch these cancers early if they do occur. And of course, taking precautions to avoid picking up HPV and other sexually transmitted diseases is still important too.

Treatments

Treating cancer is a challenge because the cancer cells are the person’s own cells. This makes it hard to target the cancer cells without also harming normal cells. Also it is necessary to kill every single cancer cell to stop the cancer from being able to start growing again.

If possible, the first step is to remove the cancer by surgery. If the cancer is completely removed this may be the only treatment needed. Other cancer treatments include chemotherapy and radiotherapy.

Chemotherapy uses chemical drugs to kill the cancer cells. The drugs target fast-dividing cells, including the cancer cells. Unfortunately, this means there are unpleasant side-effects from the loss of other fast-dividing cells, including in the digestive system and those that grow hair (this is why chemotherapy treatments often lead to hair loss).

Radiotherapy uses radiation to kill the cancer cells. The radiation is very carefully targeted to avoid damaging nearby tissues. But radiotherapy still has unpleasant side effects including nausea and hair loss.  
More-modern treatments include targeting cancer cells directly using monoclonal antibodies. Antibodies are small molecules that the body’s immune system uses to label things that ‘shouldn’t be there’. Antibodies are used to flag up viruses, bacteria and other invaders so that our white blood cells know to destroy them. By designing antibodies that attach to the cancer cells (and only to the cancer cells), it’s possible to get the body’s own immune system to kill them.

In addition to directly treating the cancer, if the cancer is an endocrine cancer it is often necessary to give hormone treatments to adjust for the effects of the cancer and treatment. If endocrine tissue has been removed during treatment, these treatments may need to continue for the rest of the person’s life.