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 spread elsewhere in the body.

Cancer cells sometimes break away from where the cancer started (the primary cancer) and travel through the blood or lymphatic system to other parts of the body. 

When this happens the cancer that develops in another part of the body is called a secondary cancer or metastasis.

What is cancer?

Cells are tiny building blocks that make up the body’s organs and tissues. 

Cells receive signals from the body, telling them when to grow and when to divide to make new cells. This is how our bodies grow and heal. 

These cells can become old, damaged or no longer needed. When this happens, the cell gets a signal from the body to stop working and die.

Sometimes these signals can go wrong, and the cell becomes abnormal. 

The abnormal cell may keep dividing to make more and more abnormal cells. These can form a lump, called a tumour.

Cells forming a tumour
Cells forming a tumour

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Not all tumours are cancer. Doctors can tell if a tumour is cancer by taking a small sample of cells from it. This is called a biopsy

The doctors examine the sample under a microscope to look for cancer cells.

A tumour that is not cancer (a benign tumour) may grow, but it cannot spread to anywhere else in the body. It usually only causes problems if it grows and presses on nearby organs.

A tumour that is cancer (a malignant tumour) can grow into nearby tissue.

Sometimes cancer cells spread from where the cancer started (the primary site) to other parts of the body. 

They can travel around the body in the blood or through lymph fluid which is part of the lymphatic system. 

When these cancer cells reach another part of the body, they may grow and form another tumour. This is called a secondary cancer or a metastasis.

Some types of cancer start from blood cells. Abnormal cells can build up in the blood, and sometimes the bone marrow. This is where blood cells are made. 

These types of cancer are sometimes called blood cancers.


The lymphatic system

The lymphatic system helps to protect us from infection and disease. It also drains lymph fluid from the body’s tissues 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 it.

Thyroid cancer cells can sometimes spread to the lymph nodes in the neck and chest.

Back to Understanding thyroid cancer

Signs and symptoms

A painless lump in the neck is the most common symptom of thyroid cancer, but there are others to watch out for.

Cancer and cell types

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

The thyroid gland

The thyroid gland releases important hormones that keep your body functioning at the correct speed.

Why do cancers come back?

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