Putting the brakes on cancer growth

Today’s Friday science feature looks — courtesy of Dr Pauline Balac, senior lecturer in biology at the University of Huddersfield — at the characteristics of cancer.

Cancer is a frighteningly common disease. There are more than 200 kinds of cancer, the most common being breast, lung, bowel and prostate cancer.

Statistically, more than one in three will develop some form of cancer during their lives.

Every two minutes in the UK, a person is diagnosed with cancer. So it was good news in April when several newspapers announced that scientists at the University of Edinburgh had discovered genetic “brakes”, which could slow down or stop diseases like cancer and multiple sclerosis.

To understand how these “brakes” could lead to new treatments for cancer, we need first to understand how cells can become cancerous.

Our bodies are made up of cells which grow and multiply by cell division, a process that must be very tightly controlled.

When a cell divides, it first makes an exact copy of its DNA, before splitting in half to form two identical daughter cells.

Cell division involves hundreds of proteins, all of which are produced from genes in the DNA. Cancer is a disease of uncontrolled cell division and usually results from defects in one or more of the genes involved in cell division.

If these genes in a cell become mutated in some way, by exposure to cigarette smoke or ultra-violet radiation for example, then that cell can start to divide uncontrollably. The defective cells can multiply to form a mass of abnormal tissue — or tumour.

In fact, the cells in a tumour usually show six different abnormalities. They produce their own growth signals, become insensitive to anti-growth signals, evade natural cell death, have an unlimited potential to divide, promote the formation of new blood vessels, invade tissues and migrate to other parts of the body.

Finding the genes involved in the cause of cancer is a lengthy business because there are so many genes involved in cell division. However, there are four main types of genes involved in this process.

Oncogenes are genes that trigger cells to start dividing. When oncogenes are activated they speed up a cell’s growth rate, like the accelerator in a car. When an oncogene is damaged, like the accelerator pedal getting stuck down, the cell and its daughters are permanently told to divide.

Tumour suppressor genes make proteins with the opposite function of oncogenes. They tell the cell not to divide and must be switched off by other proteins before a cell can grow. These are like the handbrake in a car, which is supposed to be on when the car is at rest. One of the most important tumour suppressor genes is known as p53.

DNA repair genes produce proteins that help to repair damaged DNA.

DNA can be damaged by many factors — especially radiation and carcinogenic chemicals. If the DNA that codes for a DNA repair protein is damaged, the ability of the cell to repair itself will be impaired, and this can allow errors to occur in other genes over time.

Suicide genes allow a cell to kill itself when something goes wrong, to prevent damage to its neighbours. There are many suicide genes, as this is a very complex and important feature of normal cells. If suicide genes become damaged, then a defective cell can keep dividing and become cancerous.

It was previously thought that a select group of “master” genes was responsible for controlling the growth of cells that cause cancer.

Scientists at the University of Edinburgh instead found hundreds of genes interacting. They will now try to find weak spots to halt tumour growth. They also believe that variations in the network of genes may explain why people develop diseases in different ways.

In the meantime, it is thought that up to half of all cancers in the UK could be prevented if people made changes to their lifestyle. Cigarette smoking causes a quarter of all deaths from cancer. Changes such as stopping smoking, reducing alcohol intake, keeping a healthy bodyweight and avoiding excessive sun exposure may prevent many cancers.

Research also suggests that a diet high in fibre with plenty of fruit and vegetables and reduced intake of red meat, processed meat, salt and saturated fats can protect against some cancers.

Not all cancers are preventable as inherited factors can account for up to 10 per cent of all cancers. Some viruses can also cause certain types of cancers. One thing is certain though, that cancers are a consequence of a society where everyone is living longer.

Around three-quarters of all cancers occur in people aged 60 or over. One hundred years ago, the average life expectancy was under 50 years. Now it is between 75 and 80. We may be living longer, but the diseases of ageing are now the ones responsible for our mortality.