Effect of Three Decades of Screening Mammography on Breast-Cancer Incidence
30年 乳房X光攝影 對 乳癌 的影響
To reduce mortality, screening must detect life-threatening disease at an earlier, more curable stage. Effective cancer-screening programs therefore both increase the incidence of cancer detected at an early stage and decrease the incidence of cancer presenting at a late stage.
We used Surveillance, Epidemiology, and End Results data to examine trends from 1976 through 2008 in the incidence of early-stage breast cancer (ductal carcinoma in situ and localized disease) and late-stage breast cancer (regional and distant disease) among women 40 years of age or older.
The introduction of screening mammography in the United States has been associated with a doubling in the number of cases of early-stage breast cancer that are detected each year, from 112 to 234 cases per 100,000 women — an absolute increase of 122 cases per 100,000 women. Concomitantly, the rate at which women present with late-stage cancer has decreased by 8%, from 102 to 94 cases per 100,000 women — an absolute decrease of 8 cases per 100,000 women. With the assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease. After excluding the transient excess incidence associated with hormone-replacement therapy and adjusting for trends in the incidence of breast cancer among women younger than 40 years of age, we estimated that breast cancer was overdiagnosed (i.e., tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million U.S. women in the past 30 years. We estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31% of all breast cancers diagnosed.
結果顯示，乳房X光攝影篩查在美國的實施使每年檢出的早期乳腺癌病例數翻倍，從112例/10萬名女性增至234例/10萬名女性，絕對增加數為122例/10萬女性。同樣，表現為晚期癌症的女性比率降低了8%，由102例/10萬名女性減至94例/10萬名女性，絕對降低值為每100 000名女性減少8例。假定主要疾病的負荷量是恒定的，122例追加診斷的早期癌症患者中僅有8例可能發展為晚期癌症。在排除荷爾蒙替代療法相關的暫態表達，並校正40歲以下女性患者乳腺癌發生率趨勢之後，研究者評估了過去30年間中130萬美國女性過度診斷的乳腺癌次數（如，篩檢中發現腫瘤但從未發展出現臨床症狀）。研究評估道，在2008年，超過70 000名女性被過度診斷為乳腺癌，占所有診斷乳腺癌病例的31%。
Despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer. Although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers, and that screening is having, at best, only a small effect on the rate of death from breast cancer.