据2月11日发表于《英国医学杂志》（BMJ）的加拿大国家乳腺筛查研究的25年研究结果，在乳腺癌辅助治疗得到普及后，年龄介于40~59岁的妇女每年进行1次乳腺X线检查在降低乳腺癌死亡率方面并不优于体格检查或常规保健(BMJ 2014 Feb.11;348 [doi:10.1136/bmj.g366])。

在始于1980年的5年筛查期内，多伦多大学的Anthony B. Miller医生及其同事从44,925名接受每年1次乳腺X线摄影检查及每年1次乳腺触诊检查的妇女中查出666例浸润性乳腺癌，从44,910名在社区常规保健后接受单次乳腺触诊检查的妇女中查出524例浸润性乳腺癌。其中，乳腺X线检查组与对照组分别有180人和171人在长达25年的随访中死于乳腺癌（平均在第22年死亡）。在筛查期内检出的乳腺癌患者的25年乳腺癌累计死亡率，乳腺X线检查组与对照组相近（危险比[HR]，1.05）。

在筛查期之后的随访期间，乳腺X线检查组与对照组又分别查出2,584例和2,609例乳腺癌。随访期间总共有1,005位妇女死于乳腺癌，其中包括351例在筛查期间诊断出乳腺癌的患者。

在初始筛查期间乳腺X线检查组查出的乳腺癌中，484例经筛查查出，176例为间隔癌，6例数据不足。乳腺X线检查组诊断出的癌症平均大小为1.91 cm，而对照组为2.10 cm。乳腺X线检查组中30.6%的癌症为淋巴结阳性，68.2%可触及，对照组有32.4%为淋巴结阳性，所有的癌症均可触及。可触及癌症一般大于仅通过乳腺X线检查查出的癌症（2.1 cm vs. 1.4 cm），并且呈淋巴结阳性的几率较高（34.7% vs. 16.5%）。

尽管在25年生存率方面，乳腺癌＜2 cm的患者优于＞2 cm者，乳腺X线检查查出的乳腺癌患者优于对照组患者，乳腺X线检查组中乳腺癌不可触及者优于可触及者（HR分别为0.46、0.79和0.58），但乳腺X线检查组与对照组的25年乳腺癌总体累计死亡率相近（HR，0.99）。该研究结果几乎与40~49岁妇女及50~59岁妇女的研究结果完全相同。

值得一提的是，在筛查期结束时，乳腺X线检查组与对照组相比又多查出了142例乳腺癌，在15年时多查出的乳腺癌例数维持在106例，提示乳腺X线检查组筛查出的浸润性乳腺癌中有22%为过度诊断，意即如若不是因为这项检查，患者终生都可能不会出现临床表现。这代表在该试验中每242例接受乳腺X线检查的妇女中就有1例乳腺癌属于过度诊断。假设在加拿大国家乳腺筛查研究中几乎所有被过度诊断的乳腺癌均为不可触及性，那么50%的经乳腺X线检查查出的不可触及的癌症属于过度诊断。

加拿大国家乳腺筛查研究由加拿大多家卫生机构和倡导组织提供支持。Miller医生报告称获得了加拿大健康与福利部提供的国家健康科学家奖金的资助。

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By: SHARON WORCESTER, Internal Medicine News Digital Network

Annual mammography in women aged 40 to 59 years was no more effective than was physical examination or usual care for reducing breast cancer mortality when adjuvant therapy for breast cancer is readily available, according to 25-year findings from the Canadian National Breast Screening Study.

During a 5-year screening period beginning in 1980, 666 invasive breast cancers were detected in 44,925 women randomized to receive annual mammography and annual physical breast examinations, and 524 were detected in 44,910 women randomized to receive a single physical breast examination followed by usual care in the community. Of these, 180 and 171 in the mammography and control arms, respectively, died of breast cancer during up to 25 years of follow-up (mean of 22 years), Dr. Anthony B. Miller of the University of Toronto, and his colleagues reported.

The 25-year cumulative mortality from breast cancer detected during the screening period was similar between the women in the mammography arm and the control arm (hazard ratio, 1.05), the investigators reported Feb. 11 in BMJ.

After the screening period, an additional 2,584 breast cancers were detected in the mammography arm and 2,609 in the control arm during the follow-up period. Overall, 1,005 women died from breast cancer during follow-up, including 351 who were diagnosed during the screening period.

Of the breast cancers detected in the mammography arm during the initial screening period, 484 were screen detected, 176 were interval cancers, and 6 were lacking data. The mean size of cancers diagnosed in the mammography arm was 1.91 cm vs. 2.10 cm in the control arm, they said.

"In the mammography arm, 30.6% of cancers were node positive and 68.2% were palpable. In the control arm, 32.4% of the cancers were node positive and all were palpable ...on average, palpable cancer were larger than cancers that were detected only by mammography (2.1 cm v 1.4 cm) and were more likely to be node positive (34.7% vs. 16.5%)," the investigators wrote (BMJ 2014 Feb.11;348 [doi:10.1136/bmj.g366]).

Although 25-year survival was better for those with tumors less than 2 cm vs. greater than 2 cm, those with breast cancer detected in the mammography vs. the control arm, and for those in the mammography arm with nonpalpable vs. palpable tumors (HR, 0.46, 0.79, and 0.58, respectively), the overall 25-year cumulative mortality from breast cancer was similar between women in the mammography arm and control arm, (HR, 0.99), the investigators wrote.

The findings were nearly identical for those aged 40-49 years, and those aged 50-59 years, the investigators noted.

Notably, at the end of the screening period, an excess of 142 breast cancers were detected in the mammography group, compared with the control group, and at 15 years, that excess remained at 106, implying that 22% of the screen-detected invasive cancers in the mammography arm were overdiagnosed, meaning that the cancer might not otherwise have become clinically apparent during the patient’s lifetime.

"This represents one overdiagnosed breast cancer for every 424 women who received mammography screening in the trial. Assuming that nearly all overdiagnosed cancers in the Canadian National Breast Screening Study were nonpalpable, 50% of mammogram detected, nonpalpable cancers were overdiagnosed," they said.

The Canadian National Breast Screening Study was supported by the various Canadian health agencies and advocacy groups. Dr. Miller was supported in part by a national health scientist award from Health and Welfare Canada.