The team that isolated the second breast cancer gene last year has evidence that there is a third breast cancer gene.
Mike Stratton, of the Institute of Cancer Research, said this week that an epidemiological study just completed by his team shows the likely existence of a third gene.
Dr Stratton's team isolated BRCA2 last year which, like the gene BRCA1 discovered before that, causes up to 2 per cent of breast cancers, or 500 cases a year.
Dr Stratton was speaking after the opening of a gene-cloning facility at the institute's Sutton base. The laboratory is dedicated to hunting for genes related to cancer. Dr Stratton is leading a group looking for genetic abnormalities which are passed down the generations. Offspring therefore run the risk of inheriting susceptibility to a cancer, such as the small number of inherited breast cancers.
"We're beginning to see that many other cancers have a familial component," said Dr Stratton. Examples include testicular, thyroid and prostate cancer, which affects 14,000 men a year.
Dr Stratton said his team has been evaluating samples from 200 families to see if they have abnormalities of the two known genes. "We are seeing that, even if we are missing some of the abnormalities in BRCA1 and BRCA2, there seem to be rather a large number of these families left without any mutations in these two genes."
Even allowing for breast cancers that have clustered by chance in families, without any hereditary component, Dr Stratton said that a third gene is "likely".