Paul Taylor has provided a summary of what is at issue in an article in the London Review of Books: Breast Cancer Screening. He provides this background:
One of the issues associated with mammography is the difficulty in extracting an accurate assessment from a complicated image.
Taylor indicates the controversy over screening is not due to the inaccuracy of the mammogram, or the monetary cost, or any unnecessary exposure to radiation that might be occurring. Rather, it is based on the fact that not all tumors that can be detected will ever evolve into a threat to life.
If people with this class of tumor are treated aggressively for cancer their quality of life will be diminished and their lives may be threatened unnecessarily by the treatment. Taylor refers to the capturing of this class of tumor in screening as "overdiagnosis."
The issue then is to assess the number of women who will benefit from screening and compare that to the number of women who will be harmed by screening, and then—somehow—decide whether the gain exceeds the unnecessary pain. Unfortunately, that is not a simple task. Clinical trials to assess such things are very expensive and take decades to complete.
Taylor discusses these early trials and the issues associated with them. They all seem to be compromised in one way or another. This has led some to dismiss them as unreliable while others have tried to extract information as best they can from whatever data they can find. Unfortunately they have arrived at quite different conclusions.
The utility of mammography in screening is also a function of time. As progress is made in treating breast cancer, the importance of early detection by general screening is diminished. Also, as the accuracy of mammography increases, the risk of over-diagnosis increases as well. These developments may have rendered the old clinical trials obsolete. The ubiquity of screening today renders a modern clinical trial almost impossible.
It seems that each nation tries to come to its own conclusion on the screening issue.
The UK has come to a conclusion and has provided some numbers, based on their assessment, to try to explain the issues to its citizens.
This assessment also concludes that about 20 percent of the cancers detected in screening are of the over-diagnosed variety.
An impressive chart is also provided to inform the public. It includes this information:
"15 are diagnosed with breast cancer. 8 are diagnosed and survive. They would have survived without screening. 3 are diagnosed with cancer that would never have become life-threatening. 3 die of breast cancer even though they were screened. 1 has her life saved from breast cancer. She would have died without screening."
Faced with this assessment, how should policy be determined? Taylor suggests that the deciding factor will not be the conclusions of politicians or medical experts. The women who feel affected by the issue will decide what policy will be—and they are in favor of screening.
On the men’s side, there is an analogous controversy about screening for prostate cancer. The numbers and methods are different, but the issues are the same.