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Why is cell growth a problem in cancer?

A cell is continuously receiving messages, both from its own genes and from other cells. Some tell it to grow and multiply, others tell it to stop growing and rest, or even to die. If there are enough 'grow' messages, the next stage of the cell's life starts. In a cancer cell, the messages to grow may be altered, or the messages to stop growing or to die may be missing. The cell then begins to grow uncontrollably and divide too often.

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Human cells showing the stages of cell division starting with interphase at the top.

How long do cancer cells live for?

Every time a normal cell divides, the ends of its chromosomes become shorter. Once they have worn down, the cell dies and is replaced. Cancer cells cheat this system - they retain their long chromosomes by continually adding bits back on. This process allows cancer cells to live forever. Cells from Henrietta Lacks, an American woman who was diagnosed with cervical cancer in 1951, are still growing. They are used in research laboratories all over the world, many years following her death.

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Breast cancer cells dividing.

Invading the body?

Most normal cells in your tissues stay put, stuck to each other and their surroundings. Unless they are attached to something, they cannot grow and multiply. If they become detached from their neighbours, they commit suicide, by a process known as apoptosis. But in cancer cells the normal self-destruct instructions do not work, and they can grow and multiply without being attached to anything. This allows them to invade the rest of the body, travelling via the bloodstream to start more tumours elsewhere (metastasis).

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Metastasis occurs when cancer cells travel via the bloodstream to start more tumours elsewhere.

Missing checkpoints?

Every time a healthy human cell divides, it copies all its genes, which are bundled up into 46 chromosomes. This process has several checkpoints to ensure that each new cell gets a near-perfect copy. But in a cancer cell, these checkpoints are often missing. The result is chaos: parts of chromosomes may be lost, rearranged or copied many times and the genes are more likely to acquire further mutations. Some of these may allow the cell to escape other checking and repair mechanisms.

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Chromosomes from a normal cell (above). In a cancer cell (below), parts of chromosomes may be lost, rearranged or duplicated.

Why are cancer cells so powerful?

All the cells in your body usually work together as a community. But if a cell acquires a gene mutation that makes it multiply when it should not, or helps it survive when other cells die, it has an advantage over the others. Eventually, the abnormal cells acquire mutations in more genes, causing uncontrolled growth. These abnormal cells have a competitive advantage over normal cells. This is like natural selection in evolution, where a species that produces more offspring has a better chance of survival.

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The growth of cancer cells (left) compared to normal cells (right).

Why don't cancer cells die normally?

In normal cells, gene damage is usually quickly repaired. If the damage is too severe, the cell is forced to die. An important protein called p53 checks for gene damage in normal cells, and kills them if the damage is too great to repair. However, in cancer cells these checking mechanisms are defective. Cancer cells often have an altered p53 protein, which does not work properly, allowing cancer cells to survive, despite their dangerously garbled genetic material.

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Microphotograph of a cancer cell.

How do cancer cells escape destruction?

When you are healthy, every part of your body has just the right number of cells: the birth and death of each one is carefully controlled. Any cells that start to multiply too much or in the wrong place are either stopped from growing, or forced into suicide by the process of apoptosis. In cancer cells, these instructions are either missing, altered or ignored. So cancer cells escape destruction, and continue to multiply in an uncontrolled way.

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Cell death is controlled in the process of apoptosis.

 

Principal Funder:

Wellcome trust

Major Sponsors:

GlaxoSmithKline life technologies