Cancer breakthrough: Study finds 350 DNA 'errors' that raise risk

Breast cancer breakthrough as scientists identify 350 DNA ‘errors’ that make women prone to developing the killer disease

  • Study of 200,000 people identified 352 genetic mutations that raise cancer risk
  • Believe these variations may warp as many as 190 genes, 150 more than thought
  • Say the ‘incredible’ finding will help pinpoint which women should be monitored

More than 350 DNA ‘errors’ that make women prone to developing breast cancer have been discovered by scientists. 

A study of 200,000 patients identified 352 genetic mutations which can influence whether a person develops the killer disease.  

Cambridge University experts, who carried out the research, believe these changes may warp as many as 190 genes. 

Less than 40 genes were previously recognised as raising the risk of breast cancer.

The findings could help pinpoint which women are predisposed to developing the disease, allowing them to be monitored more closely than others. 

With more 55,000 new cases every year, breast cancer is the most common type of the disease in the UK. In the US it affects 270,000 people every year.

DNA, the blueprint for the human body, carries genetic information and has all the instructions that a living organism needs to grow, reproduce and function.

There are more than 350 DNA ‘errors’ that make women prone to developing breast cancer, research by Cambridge University suggests (stock)

Humans contains between 20,000-25,000 genes – 99.9 per cent of which are identical from person to person.

The other 0.1 per cent of genetic variants are what make people unique, altering their hair colour, skin tone or even the shape of their face.

But these changes can also have profound negative effects, including increasing individuals’ susceptibility to disease.

Most diseases, including breast cancer, are complex and no single genetic variant or gene causes them.

Breast cancer is one of the most common cancers in the world. Each year in the UK there are more than 55,000 new cases, and the disease claims the lives of 11,500 women. In the US, it strikes 266,000 each year and kills 40,000. But what causes it and how can it be treated?

What is breast cancer?

Breast cancer develops from a cancerous cell which develops in the lining of a duct or lobule in one of the breasts.

When the breast cancer has spread into surrounding breast tissue it is called an ‘invasive’ breast cancer. Some people are diagnosed with ‘carcinoma in situ’, where no cancer cells have grown beyond the duct or lobule.

Most cases develop in women over the age of 50 but younger women are sometimes affected. Breast cancer can develop in men though this is rare.

Staging means how big the cancer is and whether it has spread. Stage 1 is the earliest stage and stage 4 means the cancer has spread to another part of the body.

The cancerous cells are graded from low, which means a slow growth, to high, which is fast growing. High grade cancers are more likely to come back after they have first been treated.

What causes breast cancer?

A cancerous tumour starts from one abnormal cell. The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply ‘out of control’.

Although breast cancer can develop for no apparent reason, there are some risk factors that can increase the chance of developing breast cancer, such as genetics.

What are the symptoms of breast cancer?

The usual first symptom is a painless lump in the breast, although most breast lumps are not cancerous and are fluid filled cysts, which are benign. 

The first place that breast cancer usually spreads to is the lymph nodes in the armpit. If this occurs you will develop a swelling or lump in an armpit.

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Instead, the combination of a number of them act together to increase the likelihood.   

In the latest study, researchers compared the DNA of 110,000 breast cancer patients against that of 90,000 healthy people. 

They identified 352 variants that may increase the risk of the killer disease. It is not yet clear exactly how many genes these target, but the researchers have estimated it to be 191. 

Of the newly-discovered genetic variants, a third predispose women towards developing hormone-responsive breast cancer.

This type of disease is found in four out of five breast cancer patients and occurs when cancer cells grow in response to the hormone estrogen. 

Fifteen per cent of the genetic variants predispose women to the harder-to-treat type, called estrogen-receptor-negative breast cancer. 

Study lead author Dr Alison Dunning said: ‘This incredible haul of newly-discovered breast cancer genes provides us with many more genes to work on, most of which have not been studied before.  

‘It will help us build up a much more detailed picture of how breast cancer arises and develops. 

‘But the sheer number of genes now known to play a role emphasises how complex the disease is.’

In the majority of cases, the genetic change affected gene expression rather than altering the type of protein itself.  

For instance, nine different variants regulate the same gene, the Estrogen Receptor (ESR1) gene.

Many other variants affect places in the DNA where the estrogen receptor protein binds, and, in turn regulates other genes. 

This highlights the importance of the ESR1 gene and its protein product, the estrogen receptor, in breast cancer development.

While each genetic variant only increases the risk of developing breast cancer by a very small amount, the researchers say that added together, these will allow them to ‘fine tune’ genetic testing and give women a much clearer picture of their genetic risk.

This will then allow doctors and clinicians to provide advice on the best strategy for reducing their risk and preventing onset of the disease.   

Co-author Dr Laura Fachal, from the Wellcome Sanger Institute in Cambridge, said: ‘We know from previous studies that variants across our DNA contribute towards breast cancer risk, but only rarely have scientists have been able to identify exactly which genes are involved.

‘We need this information as it gives us a better clue to what is driving the disease and hence how we might treat or even prevent it.’ 

The results, published today in the journal Nature Genetics, provide the most comprehensive map of breast cancer risk variants to date. 

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