Close relatives of women who have had cancer in both breasts and also carry a faulty version of the CHEK2 gene have a greatly increased risk of breast cancer – according to a report in the Lancet.*
Cancer Research UK scientists at the London School of Hygiene and Tropical Medicine (LSHTM) and Breakthrough Breast Cancer Research Centre ascertained the incidence of breast and other cancers among the parents, brothers, sisters and children of 469 women who had bilateral cancer (affecting both breasts).
These women were tested for a possible breast cancer gene called CHEK2. Almost one in three women with the normal version of the CHEK2 gene had a close relative with breast cancer. But six of the seven women who carried the faulty version of the gene had at least one first degree relative with breast cancer.
Study leader Professor Julian Peto, based at LSHTM, says: “Relatives of women with bilateral breast cancer plus a normal CHEK2 gene have their breast cancer risk trebled. But relatives of those who carry the faulty gene have an even higher risk.
“The faulty version of CHEK2 is a relatively rare low risk gene so screening the general population for this gene is not worthwhile. But our results suggest it may be useful to test women who have a close relative with bilateral breast cancer for low risk genes such as CHEK2.
“Our study also shows for the first time that fathers and brothers of bilateral breast cancer patients have a substantially increased risk of prostate cancer. This risk also seems to be further increased in male relatives who carry the faulty CHEK2 gene.”
*Vol. 366; Issue: 9496
Professor Alan Ashworth, director of the Breakthrough Breast Cancer Research Centre, says: “We’ve shown for the first time that genes originally thought to carry a small breast cancer risk can act in combination with other low-risk genes to dramatically increase a woman’s chance of developing this disease.
“As the majority of breast cancers are probably not caused by single genes, but by multiple genes acting together, it is now imperative that we identify other low-risk genes.
“While we hope that CHEK2 screening becomes an option Breakthrough believes it’s vital that all women aged 40-49 with a significant family history of breast cancer have access to annual mammography, as recommended by NICE. This could play a significant part in helping to detect this disease early.”
Professor John Toy, medical director of Cancer Research UK, says: “This research indicates a significant increase in breast cancer risk in both women and men where there is a family member with bilateral breast cancer. This is increased further still when there is also a damaged CHEK2 gene.
“The link to prostate cancer is interesting although the number of reported cases is small. More research is warranted to determine possible benefits of targeted screening in this relatively small population.”
Professor Peto’s work was carried out at the London School of Hygiene and Tropical Medicine and Breakthrough Toby Robins Breast Cancer Research Centre, based at the Institute of Cancer Research in London. It was funded by Cancer Research UK.
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Approximately 2000 bilateral breast cancer cases are diagnosed in the UK each year. About two per cent of cases are likely to be carriers of the faulty CHEK2 gene. Testing these 2000 women would be useful in estimating individual risks of close relatives.
The paper shows that 30 per cent (139 out of 469) of bilateral cases had at least one first degree relative with breast cancer and seven per cent (33 out of 469) had a relative with prostate cancer.
It also showed that 86 per cent (six out of seven) of bilateral cases with the CHEK2 mutation had at least one first degree relative with breast cancer and two out of seven had a relative with prostate cancer.
Women with faulty BRCA1 and BRCA2 genes are known to have a high risk of breast cancer. Up to 80 per cent of these women will develop breast cancer at some point in their lives.
But only around two per cent of the 41,000 UK cases of breast cancer diagnosed each year are due to faulty BRCA genes.
Prostate cancer is the most common cancer diagnosed among men with more than 30,000 cases diagnosed each year in the UK. Around 10,000 men die of the disease each year.
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The Breakthrough Toby Robins Breast Cancer Research Centre is the UK’s first facility dedicated to breast cancer research into prevention and treatment, based in the Mary-Jean Mitchell Green Building at The Institute of Cancer Research.