Science: Kudos and chaos in a cancer breakthrough: The long-awaited discovery of a gene that causes breast tumours may cause as many problems as it solves, says Jon Turney

Before the end of the year, so the betting goes, scientists will have pinpointed a gene that causes breast cancer. The discovery is sure to make front-page news worldwide. But researchers are concerned that millions of women at risk from cancer may be misled.

'Because breast cancer is a very common disease, a large number of women may believe that they are at risk, and that a test has something to offer. On the whole, they will be wrong,' says Martin Richards of the Centre for Family Research in Cambridge.

There are many factors which may mislead: sloppy reporting in the media will be just one. Among the other influences are competition between scientists and the institutions that fund research; commercial promotion of gene testing; and the difficulties the public may have in assessing information about risks and in understanding the behaviour of the gene.

Such factors are already at work. If they continue unchecked, then the good news could quickly turn bad, as hard-pressed health workers try to cope with public reaction.

So what will this problematic discovery consist of? Since October 1990, when Mary-Claire King, of the University of California at Berkeley, first focused the search, researchers have known that the gene - known as BRCA1 - exists, and roughly where it is.

There is a popular misconception that a single gene causes a single effect. Inevitably, therefore, BRCA1 will be known as 'the gene for breast cancer', but this is only partly true.

When it does not work properly, BRCA1 can certainly cause breast cancers. The latest risk estimate, published in the Lancet in March by a team led by Deborah Ford, of the Institute of Cancer Research in Surrey, suggests that a woman carrying the altered form of the gene has an 80 per cent chance of contracting breast cancer before she reaches 70.

But, and it is a big but, only around 5 per cent of all breast cancer cases are linked to mutations inherited from the patient's parents, and only around half of these are due to BRCA1.

However the argument also goes the other way. There are some people in families with inherited susceptibility to breast and ovarian cancers, who do not have the altered gene but who do develop breast cancer. Presumably, like the other 25,000 British women who contract the disease each year, they do so for reasons other than the gene. The patterns analysed in the Lancet suggest that there are at least two genetic abnormalities that have different effects on the risk ratios.

Most cancer researchers think that the inheritance of a BRCA1 mutation represents one stage of a multi-step process which is seen in every case of breast cancer - and that the same genetic change can arise spontaneously in a previously normal cell.

Even after the BRCA1 gene is discovered, further research will be needed to tease out the steps in the process of carcinogenesis. While this research continues, doctors who treat anxious patients daily will be faced with women demanding genetic testing.

The hype will not just be 'all got up by the press'. As the search for the gene nears its target, co-operation between scientists has given way to fierce competition, with great kudos in prospect for the winner. In Britain, the rivalry is intensified by the fact that the main groups involved are funded by the two main cancer research charities - the Cancer Research Campaign and the Imperial Cancer Research Fund - which compete for public donations and are therefore anxious to promote their role in any discovery linking genes and cancer.

'I think it's inevitable that the press will treat this as a major breakthrough,' says Dr Richards, 'and it will clearly be a coup for any major grant-giving body to be associated with the discovery of this gene.'

Then there is the commercial potential. One of the leaders in the race, Mark Skolnick of the University of Utah, has already set up a company that plans to patent a test for the gene if he finds it first. As Bruce Ponder, professor of cancer genetics at Cambridge University, put it recently: 'My worry is that all these private labs are sitting there salivating over all the money they are going to make.'

None of this will make life easier for those treating patients in breast cancer clinics. At the moment, women seeking counselling tend come from families with histories of deaths from cancer. They do not need telling that susceptibility to the disease can be inherited. But as more and more women learn of this possibility, the demands on the few specialist counsellors will increase.

And for many women and their families, there are problems understanding the implications of the new information. Families with histories of the effects of BRCA1 have often developed ideas of their own about what is happening. Daughters may believe that they will develop cancer at the same age as their mothers did. And few have any notion that the gene for what they perceive as a woman's affliction can be passed on by fathers as well as mothers.

Any genetic test will cover only part of the risk of breast cancer. And although tests can be offered, there is no real treatment to follow. Those identified as being at increased risk can be monitored for early tumours, but nothing can be done until the cancer develops. As for prevention, even the drastic step of having both breasts removed - already taken by a handful of women in the UK - is not a guarantee of safety as some tissue may be left behind.

These problems are typical of those likely to multiply as the human genome programme gathers pace. The new discoveries will help to usher in a new era of 'predictive medicine', in which all of us can acquire new knowledge about which illnesses we are likely to inherit.

But there will be lags, often long ones, between developing tests and treatment. Women worried about breast cancer are set to be the first large group to experience the ambiguities and anxieties this will create.

The writer is a Wellcome Fellow in the Department of History, Philosophy and Communication of Science at University College, London.