What is cancer?

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

Sometimes, this process 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.

Cells forming tumour
Cells forming tumour

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


Primary cancer

The place where a cancer starts in the body is called the primary cancer, or primary site. The cancer type is usually named after the part of the body where it first started to grow. For example, a cancer that starts in the lung is called a lung cancer.


Secondary cancer

A secondary cancer happens when cancer cells break away from a primary cancer and spread to another part of the body. It can spread to more than one part of the body. The cancer cells travel through the blood or lymphatic system. The cancer cells that have spread may go on dividing and form a new cancer, somewhere else in the body. A secondary cancer is also called a metastasis.

A secondary cancer is made up of the same type of cancer cells that formed the primary cancer. For example, a cancer that starts in the lungs and spreads to the liver is made up of lung cancer cells, and not liver cancer cells. So it is still treated as a lung cancer. It might be referred to as metastatic lung cancer. But if a cancer starts in the liver, it is called a primary liver cancer.


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.

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Types of CUP

Doctors may be able to find out the type of cell the cancer started in. This can help them decide on the best treatment.