Are Screening Mammograms Essential?
I recently read the 2012 book, Mammography Screening: Truth, Lies and Controversy, written by Danish doctor, Peter C. Gøtzsche. It is a very unsettling book if you are a firm believer in the value of annual screening programs for breast cancer.
Cancer is a group of diseases, each of which is very dissimilar. Many cancers grow very slowly or not at all. Other cancers actually even regress and disappear.
In Dr. Gilbert Welch’s book, Less Medicine, More Health, he describes a new conceptual model of cancer - a barnyard of cancers. The barnyard animals include turtles, rabbits, and birds. The goal is to not let any of them escape.
The turtles aren’t going anywhere because they are the lazy, slow, nonlethal cancers. The rabbits are ready to hop out anytime. They are potentially lethal cancers that might be stopped by early treatment. Then there are the birds. These are the most aggressive cancers, the ones that have already spread by the time they are detected and they are mostly beyond cure.
Screening programs can only help with the rabbits. The turtles don’t need treatment and the birds can’t be helped.
The birds are the reason that randomized trials of screening only show a small reduction in the number of cancer deaths. The rest of the bird cancer patients still die from their cancer - despite screening.
Because there is better treatment now, such as the advent of adjuvant chemotherapy and hormonal therapy, screening becomes less important. Dr. Welch says the reason we don’t screen the population for pneumonia is because treatment is so effective.
Our ability to treat women who have cancers big enough that they themselves are aware of them (cancers that are obvious without screening), makes screening mammography programs less useful.
Dr. Gøtzsche writes that because of the slow growing cancers, the first thing we know about cancer screening is that it leads to overdiagnosis and subsequent overtreatment. Overdiagnosis is the detection of cancers that would not have been identified clinically in someone’s remaining lifetime. That cancer is inconsequential.
Through autopsy studies, is has been found that cancer is so common that it is likely that all middle-aged people have cancer somewhere in their body.
Most people think of ‘having cancer’ means being ill with cancer.
In the screening setting it means something entirely different. Because it is possible to detect cancer in virtually everybody over a certain age, if only we are investigated carefully enough, ‘having cancer’ may mean nothing other than harbouring harmless cell changes that will not give any symptoms for the rest of our lives.
The problem is that we cannot distinguish between these harmless cancers and those that are dangerous. Therefore, the standard is to treat them all. For example, virtually all overdiagnosed breast cancers are treated by surgery, many with radiotherapy and some with chemotherapy.
A cancer screening always causes harm. The important question is whether screening reduces mortality from the cancer and, if so, whether the reduction is large enough to justify the harms inflicted on the healthy population.
The two uncertainties involved in deciding whether a woman has breast cancer, reading the mammogram and interpreting the biopsy, mean that some women who are diagnosed with breast cancer at screening do not have breast cancer. Errors of this kind cannot be avoided, but they are far less likely to occur when patients consult a doctor because of symptoms.
It is much more likely that a woman with symptoms has breast cancer than the likelihood that a woman invited to screening has breast cancer. Therefore, it is inevitable that many more erroneous diagnoses are made relative to the number of correct diagnoses when people are screened, compared with usual clinical practice.
If we wish to reduce the incidence of breast cancer, there is nothing as effective as avoiding getting mammograms. It reduces the risk of getting breast cancer by one-third.
~The US Center for Medical Consumers
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©2024 Melinda Coker
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