四项是同龄组研究，也就是说研究开始时对一个健康人群做遗传筛查，然后观测其后的15年他们中哪些人会患上乳腺癌，哪些人不会。

Four were cohort studies in which a healthy population was genetically screened at the outset and followed for 15 years to see who developed breast cancer and who did not.

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新的胚胎筛检技术称为基因组杂交比较，允许医生从几天大的胚胎上提取细胞。

The new screening tecnique, called comparative genomic hybridisation, allows doctors to remove cells from an embryo when it is a few days old.

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在13个人口群中，7个被随机分配到1996年至2004年的3轮筛查，而另外6个（对照组）获得的是标准护理。

Of 13 population clusters, seven were randomly allocated to three rounds of screening between 1996 and 2004, while standard care was provided in six (control arm).

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