In medicine, beliefs and ideas get very ingrained. Some, such as screening mammography become sacred cows. And when sacred cows are questioned the reaction is more akin to dealing with heresy than dealing with science. This was on display again with yet another long-term trial showing little benefit from screening mammography.
This latest study is not the first to demonstrate that in isolation, screening mammography is not life saving. Even worse there is significant harm from over diagnosis and treatment of lesions, which would never have been a problem.
As expected the mammography industry went into attack mode criticizing the study, its methods and the people behind it. There was no effort put into disputing the facts of the matter.
The Canadian study published in the BMJ looked at follow up data on 89,835 women over a 25-year period. It found no difference in either all cause mortality or deaths from breast cancer (505 versus 500 in 25 years) in women who did or did not have regular mammograms. It also showed that 20% of cancers found on screening were not going to be a threat to health and did not need treatment.
I would point out that previous reviews have put the over diagnosis rate as high as 40%.
The researchers had sought to determine if there was any benefit in finding cancers too small to feel. The answer found was that there is NOT!
This is not the first trial to show lack of benefit from screening mammography. A large review published in the New England Journal Of Medicine in 2012 showed over 30 years a doubling in the finding of early stage breast cancer but virtually no reduction in late stage cancers. In other words a lot of cancers, which would not kill women, were being found whilst those that might be fatal are not being found.
This sits at odds with the public message about “life saving” mammograms. The worst aspect, in my opinion is the number of women who have been told that their lives have been saved by treatment, which in reality they did not need for lesions, which would not have affected them. These are the ones who have been over diagnosed. In the 30-year review this totaled some 1.3 million women!
So what is the average woman to make of all this. Firstly we need some perspective about life saving tests. To quote Otis Brawley Medical Director of the US Cancer Society; “…(American) medicine has overpromised when it comes to screening. The advantages of screening have been exaggerated”.
I would add to that that the side effects or harms have been at best downplayed and at worst ignored.
The decision as to whether to be screened or not needs to be a personal one. This is based on knowing all the facts and not just the positive spin promoted by the screening industry. This decision needs to take into account individual history and family history and also how the person feels about their health. Some want to be tested and don’t care if they are over diagnosed. Others do not want tests and treatments unless they are actually needed. There is no absolute right or wrong.
And therein lies the key. Screening involves all women of a certain age for no reason other than they are women and have reached a certain age. It does not take into account personal circumstances. Worse still is the pressure from the screening industry to have tests with attempts to lay guilt on women who choose not to.
Every study has its faults. Every study can be criticized. As Aaron Carroll wrote we need to consider the biases of both those doing and criticizing the study. He made a telling point;” If you are not going to be swayed by a randomized controlled trial of (nearly) 90,000 women with 25 year follow up, excellent compliance and damn good methods, it might be time to consider that there’s really no study at all that will make you change your mind”.