What is cancer?

Cancer starts in our cells. Cells are tiny building blocks that make up the organs and tissues of our body. Usually, these cells divide to make new cells in a controlled way. This is how our bodies grow, heal and repair.

Sometimes, this goes wrong and the cell becomes abnormal. The abnormal cell keeps dividing and making more and more abnormal cells. These cells form a lump, which is called a tumour.

Not all lumps are cancerous.

  • A lump that is not cancerous (benign) cannot spread to anywhere else in the body.
  • A lump that is cancer (malignant) can grow into surrounding tissue.

Cancer cells sometimes break away from the primary cancer and travel through the blood or lymphatic system to other parts of the body. Cancer cells that spread and develop into a tumour somewhere else in the body are called a secondary cancer.

What is cancer?

Cancer starts in cells in our body. Cells are tiny building blocks that make up the organs and tissues of our bodies. They divide to make new cells in a controlled way. This is how our bodies grow, heal and repair. Cells receive signals from the body telling them when to divide and grow and when to stop growing. When a cell is no longer needed or can’t be repaired, it gets a signal to stop working and die.

Cancer develops when the normal workings of a cell go wrong and the cell becomes abnormal. The abnormal cell keeps dividing making more and more abnormal cells. These eventually form a lump (tumour). Not all lumps are cancerous. Doctors can tell if a lump is cancerous by removing a small sample of tissue or cells from it. This is called a biopsy. The doctors examine the sample under a microscope to look for cancer cells.

A lump that is not cancerous (benign) may grow but cannot spread to anywhere else in the body. It usually only causes problems if it puts pressure on nearby organs.

Diagram of cells forming a tumour
Diagram of cells forming a tumour

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A lump that is cancer (malignant) can grow into nearby tissue. Sometimes, cancer cells spread from where the cancer first started (the primary site) to other parts of the body. They can travel through the blood or lymphatic system. When the cells reach another part of the body, they may begin to grow and form another tumour. This is called a secondary cancer or a metastasis.


The lymphatic system

The lymphatic system helps to protect us from infection and disease. It also drains lymph fluid from the tissues of the body before returning it to the blood. The lymphatic system is made up of fine tubes called lymphatic vessels that connect to groups of lymph nodes throughout the body.

The lymphatic system
The lymphatic system

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Lymph nodes (sometimes called lymph glands) are small and bean shaped. They filter bacteria (germs) and disease from the lymph fluid. When you have an infection lymph nodes often swell as they fight the infection.


Who gets cancer?

Each year over 330,000 people are diagnosed with cancer in the UK. In this section are some facts about how cancer affects different age groups of people and the most common types of cancer people get.

Age

It has been estimated that more than one in three people (33%) will develop cancer at some point in their lifetime.

Cancers can occur at any age, but the risk of developing cancer increases with age. Cancer isn’t common in children or young people.

  • More than a third (36%) of all cancers are diagnosed in people aged 75 or over.
  • Over half (53%) of all cancers occur in people aged 50-74.
  • About 1 in 10 (10%) of cancers are diagnosed in people aged 25-49.
  • Less than 1 in 100 (1%) of cancers are diagnosed in teenagers and young adults aged 15-24.
  • Less than 1 in 100 (1%) of cancers are diagnosed in children, aged 14 years or under.

Common cancers

Some cancers are very common and others are very rare. The most recent statistics for the UK (from 2011) show that for men the most common cancer is prostate cancer (25% of all cancers in men), followed by lung cancer (14%), colon and rectal cancer (14%) and bladder cancer (4%).

For women, the statistics show that the most common cancers are breast cancer (30%), lung cancer (12%), colon and rectal cancer (11%) and womb cancer (5%).

Nearly a third (30%) of all cancers diagnosed in children are leukaemia.

Teenagers and young people (aged 15-24) are more likely to be diagnosed with a lymphoma (21%) or a germ cell tumour (15%) like testicular cancer.

The most common types of cancer diagnosed in adults aged 25-49 are breast cancer, melanoma, colon and rectal cancer, testicular and cervical cancer.

Lifestyle and cancer

There are over 200 different types of cancer. We don’t know the cause of most of these, but we know about some of the risk factors that can increase or influence a person’s risk. Increasing age is a risk factor that we can’t do anything about. But we can make lifestyle choices about some of the other risk factors, such as:

  • stopping smoking
  • eating a balanced diet
  • avoid becoming overweight, or if you are overweight, try to reduce your weight
  • cutting down our alcohol intake
  • getting regular exercise.

We’re getting better at recognising and treating cancer, so today many people with cancer can be cured. Even if a cancer can’t be cured, it can often be controlled with treatment for months or years.

We have information on all the main types of cancer and on some of the rarer cancers.


Back to Understanding

Cancer and cell types

Cancers are grouped into types. Types of cancer often behave and respond to treatments in different ways.

How is it treated?

There are five main types of cancer treatment. You may receive one, or a combination of treatments, depending on your cancer type.

Why do cancers come back?

Sometimes, tiny cancer cells are left behind after cancer treatment. These can divide to form a new tumour.