What is cancer?

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Cancer is a group of diseases in which the cells grow uncontrollably, and have the ability to spread to other parts of the body. There are over 200 different types of cancer, each with its own characteristics. When cancer spreads, it takes its own characteristics with it. For example, if kidney cancer spreads from the kidney to the liver, the cells in the tumour in the liver will look like kidney cancer cells.

Our bodies are made up of hundreds of trillions of cells. Each tissue and organ is made of cells, which are all very different depending where they are in the body, for example in the liver, heart, blood or kidneys. Our bodies are always making new cells to enable us to grow, to replace worn-out cells, or to heal damaged cells after injury. Usually, this process is very controlled by the genes within the cells.

Cancer cells develop as a result of changes to these genes, called mutations. These changes may be caused by a number of factors, including environmental, dietary and genetic factors (which are inherited from parents). The cancer cell grows and multiplies to form a growth or mass, called a tumour. A tumour forms because the rate the cancer cell grows and multiplies is faster than the rate of cell death.

Tumours can be either malignant or benign. Malignant tumours are cancerous tumours. Malignant tumours have a number of characteristics different to that of normal cells. Cancer cells are also able to spread away from the original tumour into surrounding tissue and other areas of the body in the blood stream or the lymphatic system (metastasise).

Benign tumours are not cancers. The main difference between benign and malignant (cancerous) tumours is that benign tumours do not spread to other parts of the body.

Where the cancer is, the type of tumour, and the genetic mutations that have caused the cancer could influence what treatment is best for that cancer.


Cancer Research UK: What is cancer?

Macmillan: What is cancer?

NHS: Overview: Cancer

Further reading: Action Kidney Cancer Essential guide: Cancer

Updated: October 2023                                                                                                                      Next review: October 2025

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