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Breast cancer gene discovered

Tuesday 6 October 2009

Experts have described the identification of a gene linked to breast cancer as “the most important discovery in the disease since the 1970s”, according to the front page of The Daily Telegraph.

The University of Cambridge research reported in this article found that 50% of breast cancer samples tested contained a damaged form of the NRG1 gene, which in its normal form is believed to act as a “tumour suppressor”. The research suggests that once the gene has been damaged it can no longer prevent tumours from forming.

While this investigation of the actions of the NRG1 gene will be of interest to the scientific community, it has only looked at a relatively small number of breast cancer tissue samples. Further studies will be needed to confirm its results and to see if the findings extend to other types of cancer. The genetics of cancer are complex, and much further investigation into cancer genetics as a whole remains to be undertaken.

Only time and research will tell whether this is the most important breast cancer discovery for over 20 years.

Where did the story come from?

Dr YL Chua and colleagues from the University of Cambridge and other UK universities carried out this research. The study was primarily funded by the Breast Cancer Campaign, with contributions from Cancer Research UK, Hutchison-Whampoa Ltd and the Ludwig Institute for Cancer Research. The study was published in the peer-reviewed scientific journal Oncogene.

What kind of scientific study was this?

This was a laboratory study investigating whether the neuregulin-1 gene (NRG1) plays a role in the prevention or formation of breast cancer.

Genes can contribute to the formation of cancers in different ways. If the gene is damaged, for example, it may become more active, which can actively cause cells to survive or divide when they should not. These types of genes are called oncogenes.

Other types of genes, known as tumour suppressor genes, can contribute in a different way: their normal function is to stop the cell from dividing inappropriately, a process that occurs when cells become cancerous. Sometimes these genes stop working, either because the piece of DNA that contains them is lost from a cell or because they are damaged in some way. When a tumour suppressor gene stops working, the cell is more susceptible to dividing inappropriately, particularly if other genetic damage occurs.

The NRG1 gene produces proteins that can cause cells to divide, but also cause them to undergo "cell suicide" and die. The researchers suspected that NRG1 might, in its normal state, suppress cancer but might also contribute to cancer when damaged, because of two previous findings:

  • The part of chromosome eight that contains the NRG1 gene has often been lost in certain cancers, such as those of the breast, colon, bladder and prostate. This suggested that NRG1 could be acting as a tumour suppressor gene.
  • In some cases of breast cancer the NRG1 gene has been damaged in a way that suggests it could be acting as an oncogene.

In this study, the researchers wanted to investigate these possible roles of NRG1 further. They started by looking at how active the NRG1 gene was in various breast cancer cells grown in the laboratory (called cell lines). They then compared how active the gene was in 63 samples of breast cancer tissue and samples of normal breast tissue taken during breast reduction surgeries (patients aged 18 to 38 years). They also looked at the possible reasons why the gene might not be very active.

They then treated breast cells in the laboratory in a way that turned down (suppressed) the activity of the NRG1 gene, looking at whether this had an effect on how much these cells divided. They then performed the same process in breast cancer cells that had active NRG1.

What were the results of the study?

The researchers found that in most of the breast cancer cell lines that they tested (16 out of 19, or 84%) the NRG1 was either switched off completely or was not very active compared to normal breast cells. They also found that the activity of the gene in breast cancer tissue tended to be similar to or less than that seen in normal breast tissue. Around half of the breast cancer tissue samples tested showed chemical changes to the NRG1 gene that would cause it to be less active, a type of change that was not seen in NRG1 in normal breast tissue.

When the researchers turned down the activity of the NRG1 gene in breast cells in the laboratory, the cells started to divide more frequently. They saw a similar effect in breast cancer cells grown in the laboratory.

What interpretations did the researchers draw from these results?

The researchers concluded that NRG1 may be the major tumour suppressor gene that is thought to lie on chromosome eight.

What does the NHS Knowledge Service make of this study?

This study has further investigated a potential role for the NRG1 gene in breast cancer, and the results suggest that the authors may have identified the gene on chromosome eight that acts as a tumour suppressor. This inital research is informative, but has so far only looked at a relatively small number of breast cancer tissue samples: further studies are needed to confirm the results and to see if the findings extend to other types of cancer.

The genetics of cancer are complex, and any subsequent research into NRG1 will be accompanied by much further research into other genetic aspects of cancer. Only after that will we know if this is the most significant breast cancer discovery for 20 years, as some newspapers have suggested.

Analysis by Bazian
Edited by NHS Website

Links to the science

Chua YL, Ito Y, Pole JCM, et al.

The NRG1 gene is frequently silenced by methylation in breast cancers and is a strong candidate for the 8p tumour suppressor gene

Oncogene, (advance online publication) October 5 2009