Scientists are calling for women to be asked if they have an identical twin sister whenever breast cancer is diagnosed.
Not only is this higher than was previously thought, but much higher than even their 100 per cent genetic identity could predict.
The researchers, based in the University of Southern California, studied 2,562 pairs of identical and non-identical twins with either one or two cases of breast cancer and compared their rates of the disease with the general population.
Previous research in collaboration with Cancer Research UK had shown that, before the menopause, where one identical twin developed breast cancer their sister had a dramatically increased risk of doing likewise.
This paper shows that even after the menopause the risk is increased; an observation that has not previously been recorded.
And not only does risk increase, but the onset of breast cancer occurs much earlier. An identical twin has a dramatically higher chance of developing breast cancer within five years of her sister than a non-identical twin or sister.
Professor Thomas Mack, Principal Investigator says: “Studying twins is a useful way to compare genetics and the environment. The fact that non-identical twins have the same risk as a mother or sister despite having a more similar upbringing can show us to what extent genetics play a part in the development of breast cancer.
“Doctors could use this information to identify women who are particularly susceptible to breast cancer and advise them accordingly.”
More regular screening and advice about prevention can be offered to high risk women. One way of easily identifying them would be to ask every patient diagnosed whether they are a twin, claim the researchers.
As knowledge of genetic and environmental risk factors grows this practice will become more and more useful in prevention and early detection of cancer and other diseases.
Sir Paul Nurse, Interim Chief Executive at Cancer Research UK says: “We know that having a close family member with breast cancer increases a woman’s risk, and this is raised dramatically when that relative is an identical twin. It makes sense to keep a more watchful eye over women who may be more susceptible to the disease.”
- British Journal of Cancer87 (3)