BRCA Mutations and Increased Risk of Cancer
Could the Known BRCA Genes be the Tip of the Iceberg?
Jun 10, 2009
The discovery of mutations in the BRCA1 and BRCA2 genes in the mid 1990s was heralded as giving women the power to find out if they were likely to develop breast or overian cancer. However with BRCA mutations accounting for such a small percentage of breast cancers, geneticists around the world are continuing the search for other genes linked to a high cancer risk.
A positive result to a BRCA1 or BRCA2 mutation means a woman has up to an 85% chance of developing breast cancer. An inconclusive result means they have the same likelihood as the rest of the population - about 10%.
Is Knowledge Power or is Ignorance Bliss?
The tests can open a Pandora's box for some, but the potential peace of mind is offered only to high-risk families affected by the known genes, leaving others to wish they had the option to unlock their own genetic secrets.
Heather Drum was diagnosed with breast cancer at 39. When her twin sister was diagnosed two years later, it brought the number of women with breast cancer in the family to six out of 18.
Although the family history is clear, Heather tested negative for the BRCA mutations. Testing positive is hard and can lead to family rifts, but Heather believes being in an "unknown" genetic group is harder.
"One of my other sisters has been in this absolute minefield of 'what if' and 'maybe' because they couldn't tell her if she has the gene or not. She's high risk because of the family history but they can't tell her if she has the prophylactic surgery if she's doing it to a healthy body or eliminating a breast cancer risk."
Finding the Genes Linked to Breast Cancer
With one renowned gene hunter comparing the human genome to a set of 23 encyclopaedias and the mutations they are searching for as a single misspelling in one of those volumes, the search is painstaking.
Volunteers from high risk families around the world donate tissue and blood to familial cancer clinics, which then provide researchers with the genetic materials they need to continue the search.
A cancer geneticist and the director of the Familial Cancer Service at Westmead Hospital in Sydney, Australia, Judy Kirk, says while some other genes have been identified, researchers have not found anything to compare to the BRCA genes.
"For the majority of families who are eligible for testing based on their history, as yet we can't find the gene fault. There are a cluster of genes which are moderate risk - for example you may have a threefold risk of breast cancer, not the same very high risk that we are seeing in BRCA1 and BRCA2."
The Breast Cancer Genes Raise Ovarian Cancer Risk
While BRCA1 and BRCA2 are named after breast cancer, testing positive to a mutation in the genes is also linked to an increased risk of ovarian cancer.
Experts recommend people concerned about their family history should speak to their doctor or a genetic counsellor who can help to determine their risk. The non-profit organization FORCE offers online support and advice.
Fourteen years after the first high-risk cancer genes were discovered researchers continue the search for more, even as they realise it might be harder this time.
"It seems to be becoming clearer now that there may be no more genes to find that cause this very high risk," Kirk says. "It could be that it's a combination of different genes that account for the problem, and that is much more difficult to find."
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