Cell division by mitosis happens throughout the body. This normally occurs due to growth or because the body needs new cells to replace old or damaged cells. Genes in the nucleus tell cells when to start dividing and when to stop.

A diagram titled 'NORMAL CELL DEVELOPMENT'. It shows a sequence of three stages: Starting from the left, there's a depiction of a 'Normal cell', an orange sphere with a darker centre. This is followed by an arrow pointing to the 'Cell division' stage, where two similar cells are next to each other. Another arrow then leads to the final stage, 'Healthy tissue', which is represented by a block of multiple interconnected cells.

Cancer is a disease caused by changes in genes, which causes normal cells to change so that they grow and divide in an uncontrolled way. The uncontrolled growth causes a lump of cells, called a tumour, to form.

When a cell becomes cancerous, it begins to divide uncontrollably. New cells are produced even though the body does not need them.

A diagram titled 'ABNORMAL CELL GROWTH'. It displays a sequence of four stages: Beginning on the left, there's an illustration of a 'Normal cell', an orange sphere with a lighter centre. An arrow leads to the 'Genetic changes' stage, showcasing a darker cell. Another arrow then points to the 'Cancerous cell division' stage, where two such darker cells are together. A final arrow leads to the 'Malignant tumour' stage, represented by a large cluster of these dark cells.

The extra cells produced form growths called tumours. Most tumours are solid, but cancers of the blood, for example, leukaemia, are an exception.

Types of Tumours

There are two types of tumours:

1. Benign

2. Malignant

A side-by-side comparison of two cross-sections of tissue. On the left, the tissue labelled 'Benign tumour' shows a cluster of uniformly pink cells surrounding a compact, dark purple mass. On the right, the tissue labelled 'Malignant tumour' has the same pink cells, but the centre features a chaotic sprawl of irregular dark purple shapes, indicating the invasive growth.

Benign tumours typically grow within a membrane, so they can be easily removed. They do not invade other parts of the body and tend to grow slowly.

  • Benign tumours are not cancerous.

Malignant tumours grow rapidly. They invade neighbouring tissues and can spread to other parts of the body through the bloodstream.

An illustrative depiction of cancer cells spreading within the human body. A cross-section of healthy tissue in the centre shows uniformly coloured red-orange cells. To the left, a blood vessel is shown with a 'Spreading cancer cell' travelling upwards, indicating its movement 'To lungs and other organs'. On the right, a lymph vessel also contains a 'Spreading cancer cell' moving upwards, signifying its direction 'To lymph nodes and other parts of the human body'. Both the blood vessel and the lymph vessel intersect with the tissue, highlighting the invasion of the cancer cell into the surrounding tissue.

  • Malignant cells are classified as cancer cells

As a malignant tumour grows and spreads, it can form smaller tumours, which are called secondary tumours. This process is known as metastasis.

Risk Factors

We can inherit an increased risk of getting certain cancers, such as:

  • Breast cancer
  • Colon cancer
  • Prostate cancer

Carcinogens are substances that are capable of causing cancer. They can occur naturally in the environment (e.g. Ultraviolet radiation in sunlight). However, carcinogens can also be produced by humans, such as the exhaust fumes released by vehicles.

Some cancers are caused by lifestyle choices. For example:

  • Carcinogens in cigarettes increase the risk of lung cancer
  • Exposure to ultraviolet (UV) radiation is linked to skin cancer
  • Alcohol consumption is linked to certain cancers


You’ve used 10 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up