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What is Cancer

What is Cancer?

Approximately one in three people will be affected by cancer at some stage in their lives. Cancer is not one disease, but many. As well as having some similar features, each cancer will have a distinctive character, which varies according to its type and location.

The human body is made up of millions of cells, which grow and divide to replace old tissue and maintain the body. Each part of your body is composed of cells, which are shaped and designed for that area. Usually, cells in the body are replaced by identical new ones when they wear out.

When things go wrong, some of the new cells are different. They begin to multiply and form a tumour or lump. This lump could be benign or malignant. Benign tumours are usually harmless and sometimes do not need treatment. Malignant tumours are cancerous.

In some cancers, the abnormal or uncontrolled growth of cells occurs in the bone marrow where blood cells are made. These cancers do not always produce a tumour or lump.

What causes cancer and how quickly the cells grow and spread, is different from person to person.

There are different types of treatment for cancer, depending on the stage and type of cancer you have and your general health. Because advances in cancer care and treatment are being made all the time, what you, your family or friends think now may not be correct or up to date. Check with your doctor or nurse if you are unsure about something you have heard or read about.

There is a future after finding out you have cancer, and every case is different. As time passes, most people find the initial shock and effects of the treatment pass and they can think once again about things other than cancer. Although there is always a chance that cancer will recur, many people become entirely free of the disease. Many more live for years without problems associated with their cancer.

Let’s start to understand a little more about what cancer is. Often if you can understand something it can feel less frightening.

Cancer is a disease caused by normal cells changing so that they divide in an uncontrolled way. The uncontrolled growth causes a growth to form called a tumour. If not treated this tumour can cause problems such as

  • Spreading into nearby normal tissues.
  • Causing pressure on other body structures.
  • Spreading to other parts of the body through the lymphatic system or blood stream

There are over 200 different types of cancer because there are over 200 different types of body cells. For example, cells that make up the lungs can cause a lung cancer. There are different cells in the lungs, so these may cause different types of lung cancer.

The place where a cancer begins is called the primary cancer. Cancers may also spread into nearby body tissues. For example, lung cancer can spread to the lining of the chest (the pleura). Ovarian cancer can spread to the lining of the abdomen (the peritoneum). This is called locally advanced cancer.

Cancer cells can break away from the primary tumour and be carried in the blood or lymphatic system to other parts of the body. There they can start to grow into new tumours. Tumours from cancers that have spread are called secondary cancers or metastases (pronounced met-as-tah-seez). A cancer that has spread has ‘metastasised’.

The various organs of the body are made up of different types of cells. Any of these cell types can grow into a primary cancer. Different types of cancer behave very differently. The type of cancer affects whether it is

  • Likely to grow quickly or slowly
  • Likely to produce chemicals that change the way the body works
  • Likely to spread in the blood or lymph system
  • Likely to respond well to particular treatments

Cancers can cause different symptoms according to where they are in the body. A cancer may press on a nerve, or another nearby body organ. It may also cause symptoms by releasing chemicals or hormones into the bloodstream.

Primary and secondary cancer

The main reason cancer can be difficult to cure is that it can spread to a different part of the body from where it started. The cancer that grows where it first started in the body is called the ‘primary cancer’. The place a cancer spreads to and then starts growing are called the ‘secondary cancer’ or ‘metastasis’. Cancer that has spread to another part of the body is called metastatic cancer.

How a cancer spreads

In order to spread, some cells from the primary cancer must break away, travel to another part of the body and start growing there. Cancer cells do not stick together as well as normal cells do. They may also produce substances that stimulate them to move. There are three main ways a cancer spreads

Local spread

Where cancers grow directly into nearby body tissues.

Through the blood circulation

The cancer must first become detached from the Primary cancer and then move through the wall of a blood vessel. When it is in the bloodstream, it is swept along by the circulating blood until it gets stuck somewhere, usually in a very small blood vessel called a capillary.

Then it must move back through the wall of the capillary and into the tissue of the organ    close by. There it must start to multiply to grow a new tumour. As you can see, this is a complicated journey. Most cancer cells do not survive it. Probably, out of many thousands of cancer cells that reach the blood circulation only one will survive to form a secondary cancer or metastasis.

Through the lymphatic system

The way a cancer spreads through the lymphatic system is very similar to the way it spreads through the bloodstream. The cancer cell must become detached from the primary tumour. Then it travels in the circulating lymph fluid until it gets stuck in the small channels inside a lymph node. There it begins to grow into a secondary cancer.

Why cancers spread where they do

Whether it is in the blood or the lymph, the moving cancer cell stops at the first place it gets stuck. In the bloodstream, this is often the first capillary network it comes across. The blood flow from most body organs goes from the organ to the capillaries in the lungs. So not surprisingly, the lungs are a very common place for cancer to spread to.

The blood from the organs of the digestive system goes through the capillaries of the liver before going back to the heart and then to the lungs. So it is common for digestive system cancers to spread to the liver. In fact, the liver is the second most common area of cancer spread.

Some cancers show unexpected patterns of spread. For example, prostate cancer often spreads to the bones. Scientists are still investigating why this happens.

Cancer cells often get trapped in the group of lymph nodes closest to the tumour. During cancer surgery, the surgeon may remove the main lymph nodes close to the area of the cancer. For example, a surgeon operating to remove a breast cancer will remove one or more of the lymph nodes from under the arm. These are the first lymph nodes that the lymph draining from the breast goes to and so are most likely to contain any escaping cancer cells.


These are areas of cancer spread (metastases) that are too small to see. If there are individual cells, or even small areas of growing cells elsewhere in the body, no scan is detailed enough to show them. In a few types of cancer, blood tests can detect certain proteins released by the cancer cells. These may give a sign that there are metastases too small to show up on a scan. But for most cancers, there is no blood test that can say whether a cancer has spread or not.

So at some point you will no doubt ask yourself – But why did I get Cancer?

There are so many different causes of Cancer that we may never know exactly what caused yours. As we said there are about 200 different types of cancer. It can start in any type of body tissue. What affects one body tissue may not affect another. For example, tobacco smoke that you breathe in may help to cause lung cancer. Overexposing your skin to the sun could cause a melanoma on your leg. But the sun won’t give you lung cancer and smoking won’t give you melanoma.

You could be forgiven for thinking that with so many potential causes, everyone will get cancer. But not everyone does. So why do some people get it and others don’t? As ever, there are a number of different factors working together.

Risky behavior

This just means indulging in something that increases your risk. It may be smoking, or drinking too much, or eating a very unhealthy diet. Some of us look after ourselves better than others. And this can have a real effect on our health. But some people look after themselves really well and still get cancer. While others don’t seem to look after themselves at all and never do.

Your immune system

The balance between the immune system and cancer is complicated but if your immune system is compromised your body’s natural ability to kill mutated cells can also be compromised


Some doctors say that if all men lived long enough they would get prostate cancer. It is true that the longer we live, the more likely we are to gather enough genetic damage to start a cancer off. Most of us die of something else, such as old age or other illnesses, before we get to that point.


Many changes in genes are accidental. Cells divide and each time they do, they have to copy their genetic code completely. Sometimes mistakes happen. Many of these accidents would be fatal to the cell and the daughter cells would die. Sometimes the damage is repaired. Some changes wouldn’t make very much difference to how the cell works. But they may take that cell one step further along the road to becoming cancerous..

Genetic predisposition

You may hear doctors or scientists talk about genetic predisposition to cancer. This means that your genetic make-up makes it more likely that you will develop cancer. It is not common, but there are such things as cancer families. These families have a much higher incidence of cancer than other families in the population. This may be particular types of cancer. But some families have all sorts of different cancers turning up in their family tree. They probably have a change (mutation) in a gene that is crucial in the development of many different cancers. Cancer specialists believe that the younger someone is when they develop an adult cancer; the more likely it is that there are genetic factors at work.

How common are ‘inherited’ cancers?

We hear a lot about people getting cancer because they have inherited a single gene fault that increases their risk. But this is relatively rare. Most cancers develop because of a combination of chance and our environment, not because we have inherited a specific cancer gene. For example, only about 3 in 100 breast cancers (3%) are due to an inherited faulty gene.

This is a fast changing area of medicine. The breast and ovarian cancer genes BRCA1 and BRCA2 were among the first cancer genes scientists identified in the 1990s. Since then researchers have found other genes that increase the risk of other cancers. They will continue to find more over the next few years.

What a family history of cancer is

Many people with cancer in the family worry that they are at greater risk of getting it themselves. But as we’ve seen, this isn’t the case for most people. Cancer mostly occurs in older people. It is a common disease. 1 in 3 people in the UK get cancer at some point in their lives. So, most families will include at least one person who has had cancer. Having a couple of relatives diagnosed with cancer when over the age of 60 doesn’t mean there is a cancer gene running in the family.

Genetics specialists estimate that only about 2 or 3 in every 100 cancers diagnosed (2 – 3%) are linked to an inherited gene fault.

The strength of your family history depends on

  • Who in your family has had cancer
  • How old they were at diagnosis
  • The more relatives who have had the same or related cancers, and the younger they were at diagnosis, the stronger your family history. And the more likely it is that cancers are being caused by an inherited faulty gene. You may have a strong family history if any of these situations apply to you
  • More than 2 close relatives on the same side of your family have had cancer (the same side of your family means either your father’s relatives or your mother’s relatives)
  • They have had the same type of cancer, or different cancers that can be caused by the same gene fault
  • The cancers developed when they were young, below the age of 50
  • One of your relatives has had a gene fault found by genetic test

Remember – cancer is most common in people over the age of 60 and is rare in young people. So cancer in older people is less likely to be due to an inherited cancer gene.