Beyond showing no benefit from mammography screening, the Canadian trial highlighted one of the practice’s major disadvantages: over-diagnosis. Indeed, 22% of those in the screened group were over-diagnosed, meaning that the cancers found would not have become clinically detectable during the woman’s lifetime.
加拿大试验不仅未能证明乳腺X光筛查的好处，还突出了上述方法的一个主要缺陷：诊断过度。事实上，筛查组22%的人都存在过度诊断现象，也就是说发现的癌症在受试者一生中都不可能得到临床检测。再加上原位癌——即尚未扩散到邻近组织的早期癌症——该比例增长至50%。