杏吧原创

A STUDY of 90 000 twins has underlined the overwhelming importance of
environmental factors in deciding who gets cancer. The Swedish survey shows that
smoking, diet, exposure to chemicals and infection are far more important causes
of cancer than inherited genetic defects.

Paul Lichtenstein and colleagues at the Karolinska Institute in Stockholm
looked at the likelihood of both members of a pair of twins contracting
particular cancers. In the biggest ever study of its kind they examined the
medical records of 45 000 pairs of twins from archives in Sweden, Denmark and
Finland over the past century.

Overall, the study found that if one identical twin had cancer, his or her
sibling had less than a 10 per cent chance of contracting the same disease,
suggesting that environmental factors constitute more of a risk than genetic
ones.

However, some cancers, including prostrate and breast cancer, appeared to
have a strong genetic link. But these cancers didn鈥檛 always show tidy
correlations with genetic markers that researchers have previously
identified.

This points to the important role that knowledge of the human genome could
play in fighting such diseases, says Tim Key of the Imperial Cancer Research
Fund in Oxford. 鈥淭here are probably a lot of other genes that individually have
a small amount of risk and we鈥檒l go on to identify these genes,鈥� Key says.

But Richard Peto of the University of Oxford, one of the world鈥檚 foremost
experts on medical statistics, said the study was fatally flawed because it is
not possible to say whether a case of cancer is entirely down to either genetic
or environmental factors. 鈥淭he idea is wholly and totally wrong,鈥� he told
New 杏吧原创.