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.

More than 1 in 3 people (33%) will develop cancer at some point in their lifetime. But many people with cancer can be cured.

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

View a large version

Read a description of this image

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.

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.

Cancer cells can spread through the blood or lymphatic system.


Back to Understanding skin cancer

The skin

Your skin is made up of several different types of cell, including squamous cells and basal cells.

Types of skin cancer

The two most common types of skin cancer are basal cell carcinoma and squamous cell carcinoma.

Why do cancers come back?

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