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Could there be a breast cancer virus?

Bupa investigative news - 26 August 2003
written by Rachel Newcombe, reporter for Bupa's Health Information Team

Breast cancer is the most common form of cancer to affect women, with one in four of all cancers occurring in the breast and more than 40,000 women diagnosed each year in the UK. The causes of breast cancer are being researched and, according to a theory from scientists in Australia, one possible cause could be a virus. The Australian researchers say that the virus is similar to one that has been found to cause breast cancer in mice.

KEY POINTS

Scientists in Australia have been researching the possibility of a breast cancer virus.

They have focused their attention on a virus known as HHMMTV. HHMMTV is short for human homologue of mouse mammary tumour virus.

HHMMTV is a virus that can infect humans and is similar to a virus that has been found to cause 95 per cent of breast cancer cases in mice.

Part of the Australian research compared breast cancer samples with normal breast tissue taken from women having cosmetic surgery. They found that 42 per cent of the women who had breast cancer tested positive for the virus, compared with only 2 per cent of women who had healthy breast tissue.

Other research by the team, published in the Journal of Clinical Cancer Research, compared incidences of the virus in breast tumours of australian and vietnamese women. The incidence of the virus was much greater in australian women than vietnamese women, suggesting that the presence of HHMMTV could be population based.

Cancer charities have expressed interest in the findings, but say much more research is needed before a link between HHMMTV and breast cancer can be firmly established.

Other factors that are known to increase the risk of developing breast cancer include age, diet, alcohol, family history and obesity. Therefore, to reduce the risk of developing breast cancer, the advice is to eat healthily, avoid obesity and avoid drinking to excess.

What were the headlines?

Breast cancer hit the headlines again with the news that a virus could play a part in causing the disease. Short reports were featured in a UK newspaper and on a UK website, with the headlines "Cancer in virus link" and "'Breast cancer virus' found" respectively. One news report included the idea that finding a virus could open up the possibility of developing a protective vaccine.

What is the bigger picture?

Scientists from the University of New South Wales and the Prince of Wales Hospital in Randwick, New South Wales have been carrying out research into the possibility of a breast cancer virus for sometime. Caroline Ford, a PhD student from the University presented an overview of their findings at the Fresh Science Forum in Melbourne, Australia on Sunday 17th August.

Their research has focused on a virus called HHMMTV (human homologue of mouse mammary tumour virus), a form of MMTV (mouse mammary tumour virus), which causes more than 95 per cent of breast cancer in mice.

During the year 2000 they set out to discover how common the virus is in the Australian population. Normal breast tissue samples were obtained from people having cosmetic surgery and were compared with breast tissue samples of breast cancer patients. They discovered that 42 per cent of Australian breast cancer samples tested positive for the virus, compared to only 2 per cent of normal breast tissue samples. Since then the researchers have also shown that the virus appears to be associated with severe forms of breast cancer and is only found in the cancerous areas of the breast tissue, not in the surrounding healthy breast tissue.

Another part of their work, published in the Clinical Cancer Research Journal in March 2003, involved a study of breast tumours in Australian and Vietnamese women. They found more instances of MMTV-like genes in the breast tissue of Australian women than Vietnamese, suggesting that the genes might only be found in some human populations.

Commenting on the research as a whole, Caroline Ford said, "Many people believe that breast cancer is purely a hereditary disease, yet hereditary breast cancer is estimated to account for only 5 per cent of all cases of breast cancer. In other words, we have little idea what causes 19 out of 20 cases. Our preliminary research indicates that a virus may be involved."

"It's an exciting discovery, but there's still a lot of work to do to get sufficient proof of the role of the virus," she said. If the virus is found to have a definite role in breast cancer development then, in theory, preventive treatments could be created against it.

"If this virus does in fact play a role, it opens up the possibility of a preventative vaccine," added Caroline. "However, we have to do much more work to prove the link."

The idea that a virus could cause breast cancer has been investigated for quite some time. Studies first began back in the 1940s, when scientists discovered that mice appeared to get breast cancer because of a factor that could be passed on to other mice. This factor was found to be a virus - MMTV. The possibility of a human breast cancer virus was raised in 1999 when Dr Robert F Garry, professor of microbiology and immunology at Tulane University Medical Centre in America, announced that he had found evidence for a human virus that was closely related to MMTV.

"The research on the HHMMTV virus and breast cancer is interesting, but there are still a lot of unanswered questions as this is early research.

"The biggest risk factor for breast cancer is increasing age - over half of all breast cancers occur in women aged more than 65 years, and it is very rare in women aged less than 30.

"If women are worried about breast cancer they can try to become more 'breast-aware' which means that women should know what their breasts look and feel like normally so that they can notice any unusual changes. If women do notice a breast lump or other breast symptom they should get advice from their GP as soon as possible.

"However, it's worth knowing that nine out of 10 lumps are not due to breast cancer."

Dr Annabel Bentley,
Assistant medical director
Bupa Group

What does this mean?

Emma Knight, from the Science Information Department at Cancer Research UK, told Bupa, "There have been quite a few studies that have shown that you can find the DNA that belong to viruses in certain breast cancers, and it seems to depend on where people live as to how much of this viral DNA they have in their bodies. However, no-one's actually established that it can cause cancer. It's there and some people with cancer tend to have a higher amount of this virus DNA than people without breast cancer, but that doesn't mean that it's the virus DNA that's causing the cancer."

"This is one of the main groups who are looking at viral DNA in breast cancer," she added. "Their research sounds credible and they have found that there's more viral DNA in certain populations."

But, even if the virus is shown to cause breast cancer, creating a vaccine to it is still a long way off. "If they do show that a virus is causing it, they could probably develop a vaccine," said Emma. "But you're looking at least 20 years down the line and they've got a lot of work to do before they can show that a virus is causing breast cancer."

A spokesperson for Breakthrough Breast Cancer, told Bupa, "The results of this research are potentially very interesting, but it is preliminary data based on a very small sample of women in Australia. Further research is needed to prove a link between the virus being present and breast cancer developing."

Anna Wood, policy analyst at Breast Cancer Care, said, "Breast Cancer Care welcomes any research that investigates the possible causes of breast cancer. At this stage the research highlights a possible link between the virus HHMMTV and breast cancer and we recommend that further research is needed in this area."

ACTION POINTS

Reduce the risk of breast cancer by maintaining a healthy diet and lifestyle.

Attend regular breast screening appointments if you're more than 50 years old.

Be "breast aware", and report any changes to your doctor immediately.

If you're concerned about the risk of cancer, talk to your doctor.

What does this mean to me?

According to Cancer Research UK and many of the breast cancer charities, knowledge about the potential virus is still in its very early stages and much more research is needed before a link can be proved.

In the meantime, however, there are other factors that are known to increase the risk of breast cancer, and it's these factors that women may be able to do something about. There's some evidence to suggest that obesity could be linked to breast cancer and that diets containing high levels of fat and alcohol also carry with them an increased risk. Other known risk factors include age (women older than 50 years are more susceptible) and family history, with women whose mother, sister or daughter who have breast cancer having double the risk.

Because diet is one of the areas that can, at least partly, be controlled, Cancer Research UK advise the following healthy diet:

  • plenty of fruit and vegetables - eating five portions of fruit and vegetables are recommended each day, including lots of different coloured produce to ensure a good intake of different vitamins and minerals
  • foods high in fibre
  • starchy foods
  • low levels of fat
  • low amounts of red meat.

Summary

The theory that HHMTV may cause breast cancer is an interesting area of breast cancer research. However, because this research is still in its early stages, much more needs to be discovered and confirmed before a definite link can be established.

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