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The title is somewhat misleading since all women were not screened in the communities where screening was offered so the title should read "Effect of the Invitation to Screening Mammography .

This is important because non-compliance reduces the effectiveness of screening. This article suggests that most of the decrease in breast cancer deaths is due to improvements in therapy with a lesser contribution from screening. There are large, published studies from Sweden and the Netherlands that disagree with these results and show that most of the decrease in deaths is due to screening and not therapy.

There are several reasons listed below that likely account for why the authors arrived at different results — the most likely one being their extremely short follow-up period.

It is clear that when screening programs begin, not everyone starts being screened on day one, but one has to wonder why, if screening began in 1995 they only have an "average of 2.2 years" follow-up? The more important question is why did they stop at 2005? It is now 2010.

Certainly with so many years since the start of screening the average length of follow-up should be greater than 2.2 years. This is a trivial amount of follow-up. The full impact of screening would not be expected so soon. Since these are numbers in a registry, the authors should easily have more up-to-date figures. They certainly should not be comparing their results to the randomized, controlled trials (RCT), which have much longer follow-up. With such short follow-up, their results are interesting, but based on the RCT, they should expect even greater benefit from screening as women are followed for a longer period of time.

Several other points are clear:

• The authors agree — screening for breast cancer saves lives. The issue is how many lives saved does it take to make screening "worthwhile".
• It is not clear that they excluded all women in the "screening" communities whose cancers were diagnosed before they actually began screening. Including women whose cancers predated actual screening, simply by the stating the starting date, does not mean they actually had the advantage of being screened.
• The Norway results are based on screening women ages 50-69 every two years.  In the United States women are encouraged to be screened every year. Clearly more lives will be saved by giving breast cancer less time to grow between screens. Even the United States Preventive Services Task Force (USPSTF) agrees that screening every two years results in deaths that could have been averted by screening every year.
• The authors claim that from 1986-2005 only 12 percent of women diagnosed with breast cancer died from their cancers. This is half what would be expected in the absence of screening. This suggests, at the least, that there was likely a great deal of screening among women whom the authors claimed were not being screened. Before they claim that there was no screening going on in the comparison (unscreened) group they should find out if that was the case, which they did not do. With such extensive record keeping it should be easy to find out how the cancers were detected. Why this was not done?
• The authors clearly show that even screening every two years leads to 33 percent fewer deaths than without screening (7.2 fewer deaths among screened women vs. 4.8 among, supposedly, unscreened women).
• The authors overlook important information by grouping the results for uninvited women (under age 50 and over age 70). There was only a slight decrease in deaths for women under age 50 over the time period. There were 1.5-1.7 fewer deaths showing little improvement for these women who were not screened. This means that therapy had little effect on women in their forties without screening. In comparison the decrease in deaths was 7.2/100,000 among women 50-69 who were offered screening.  
• Women age 70-84 in the screening counties (but, supposedly unscreened) somehow had over 40 percent fewer deaths when compared to those in the unscreened counties  (10.8 vs. 6.1) yet they were all, supposedly, not being screened. Why the major difference?  Were these women in the screening counties being screened? We must assume they were receiving the same therapy. Was this a reflection of screening while the women were younger than age 70 removing many of the cancers that killed in the unscreened counties? Was there a fundamental flaw in the study design?

The authors confirm that screening saves lives. It has now become a debate of degree. Therapy is only successful when cancers are found earlier. Their very short follow-up, without being certain that they did not dilute the benefit with cancers diagnosed before actual screening, and without knowing the actual contamination of the "unscreened" group, makes these results, at best, premature.  

Would the study authors, and the doctor who wrote the accompanying editorial, suggest that it is not worthwhile if we only decrease deaths by 30 percent? There is no universal cure in sight. Until one is found, annual screening and early detection, beginning by the age of 40, offer women the best chance for cure. This esoteric debate is confusing and draining for women and their physicians.

It is time to accept that screening, beginning at the age of 40, is saving tens of thousands of lives. We need to concentrate on finding ways to add to this major accomplishment.  

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Source: ACR