British Columbia Cancer Agency, Vancouver, BC.
CMAJ. 2013 Jul 9;185(10):E492-8. doi: 10.1503/cmaj.121791. Epub 2013 Jun 10.
There has been growing interest in the overdiagnosis of breast cancer as a result of mammography screening. We report incidence rates in British Columbia before and after the initiation of population screening and provide estimates of overdiagnosis.
We obtained the numbers of breast cancer diagnoses from the BC Cancer Registry and screening histories from the Screening Mammography Program of BC for women aged 30-89 years between 1970 and 2009. We calculated age-specific rates of invasive breast cancer and ductal carcinoma in situ. We compared these rates by age, calendar period and screening participation. We obtained 2 estimates of overdiagnosis from cumulative cancer rates among women between the ages of 40 and 89 years: the first estimate compared participants with nonparticipants; the second estimate compared observed and predicted population rates.
We calculated participation-based estimates of overdiagnosis to be 5.4% for invasive disease alone and 17.3% when ductal carcinoma in situ was included. The corresponding population-based estimates were -0.7% and 6.7%. Participants had higher rates of invasive cancer and ductal carcinoma in situ than nonparticipants but lower rates after screening stopped. Population incidence rates for invasive cancer increased after 1980; by 2009, they had returned to levels similar to those of the 1970s among women under 60 years of age but remained elevated among women 60-79 years old. Rates of ductal carcinoma in situ increased in all age groups.
The extent of overdiagnosis of invasive cancer in our study population was modest and primarily occurred among women over the age of 60 years. However, overdiagnosis of ductal carcinoma in situ was elevated for all age groups. The estimation of overdiagnosis from observational data is complex and subject to many influences. The use of mammography screening in older women has an increased risk of overdiagnosis, which should be considered in screening decisions.
由于乳房 X 光筛查，乳腺癌过度诊断的问题日益受到关注。我们报告了不列颠哥伦比亚省在人群筛查开始前后的发病率，并提供了过度诊断的估计。
我们从不列颠哥伦比亚癌症登记处获得了乳腺癌诊断数量，从不列颠哥伦比亚省筛查乳房 X 光计划中获得了 1970 年至 2009 年间 30-89 岁女性的筛查史。我们计算了浸润性乳腺癌和导管原位癌的年龄特异性发病率。我们按年龄、日历期和筛查参与情况比较了这些发病率。我们从 40 至 89 岁女性的累积癌症发病率中获得了过度诊断的 2 个估计值：第一个估计值比较了参与者和非参与者；第二个估计值比较了观察到的和预测的人群发病率。
我们计算出，仅浸润性疾病的基于参与的过度诊断估计值为 5.4%，而包括导管原位癌时为 17.3%。相应的基于人群的估计值为-0.7%和 6.7%。与非参与者相比，参与者的浸润性癌症和导管原位癌发病率更高，但在筛查停止后发病率较低。人群中浸润性癌症的发病率在 1980 年后增加；到 2009 年，60 岁以下女性的发病率已恢复到 20 世纪 70 年代的水平，但 60-79 岁女性的发病率仍居高不下。所有年龄组的导管原位癌发病率均有所增加。
我们研究人群中浸润性癌症的过度诊断程度适中，主要发生在 60 岁以上的女性中。然而，所有年龄组的导管原位癌过度诊断率都较高。从观察数据中估计过度诊断情况复杂，受到许多因素的影响。在老年女性中使用乳房 X 光筛查会增加过度诊断的风险，在筛查决策中应予以考虑。
