ACR on the CNBSS Mammography Study: “Deeply Flawed and Widely Discredited”
Reading Time: 4 minutes read
A disturbing study about the effectiveness of mammography was released to the public on February 11 in the British Journal of Medicine. The New York Times wrote about the study, providing such summaries as:
“… the death rates from breast cancer and from all causes were the same in women who got mammograms and those who did not. And the screening had harms: One in five cancers found with mammography and treated was not a threat to the woman’s health and did not need treatment such as chemotherapy, surgery or radiation.” – New York Times, February 12, 2014
The goal behind this study was for researchers to determine if there is any advantage to discover breast cancers that were too small to feel. The study claimed that there is no advantage, but the American College of Radiology (ACR) came to the rescue to debunk this claim.
The ACR came right out to call the study “deeply flawed and widely discredited” and backed up its words. Citing reviews from experts, the ACR learned that the trial used second-hand mammography machines, which were not the most up-to-date at the time the study was conducted. The ACR went on to say:
“The images were compromised by ‘scatter’ which makes the images cloudy and cancers harder to see since they did not employ grids for much of the trial. Grids remove the scatter and make it easier to see cancers. Also, technologists were not taught proper positioning. As such, many women were not properly positioned in the machines, resulting in missed cancers. And the CNBSS radiologists had no specific training in mammographic interpretation.” – American College of Radiology, February 12, 2014
Additionally, the ACR brought about claims that the CNBSS violated the rules of conducting a randomized, controlled trial (RCT). This was because each woman who participated in the study had a clinical breast examination by a trained nurse so that they knew which women had lumps and which women indications of more advanced cancer. For a RCT to be valid, the women assigned to the screening group or the control group must be random, and this was certainly not the case.
One issue with the wording in the news articles that covered the CNBSS study is that they are including mammography exams into the same category as treatment. But these are two different areas. Mammography and the advancements made in the field are leading to earlier detection of breast cancer. Patients are then referred to their physicians who then determine the diagnosis best course for treatment.
Along with the ACR, the mammography medical community made sure its voice was heard after large news outlets began picking up the story. On the radiology trade publication site AuntMinnie, Dr. László Tabár and Tony Hsiu-Hsi Chen, DDS, PhD, wrote an op-ed about the CNBSS study and how the medical field has been dismissing it for years, citing it as being “a failure from the beginning.”
They go on to say that even the World Health Organization’s International Agency for Research on Cancer (IARC) workshop excluded the study in 2002 because the study was not population based and “the Canadian trials could not evaluate the independent impact of mammography because of the confounding effect of physical examination.” At the end of their letter, Drs. Tabár and Chen quote Dr. Norman Boyd, who had this to say about the CNBSS study 21 years ago in Radiology (1993, Vol. 189:3, pp. 661-663):
“Taken at face value, the results of the [CNBSS] argue for abandoning mammographic screening as a population-based means of controlling death rates from breast cancer. We believe such a conclusion to be unjustified and unsupported by the findings of the [CNBSS] … [and] the results of these trials should not be used to change the prevailing scientific view of the potential benefits of screening with mammography.”
Those of us that have been involved in mammography since the 70s have seen enormous advances in the understanding of what is needed to ensure early detection and the effectiveness of mammography. The industry has helped to improve the image quality since the Canadian study with advances in analog film, improvements in x-ray units and of course the introduction of digital mammography and digital breast tomosynthesis. There have also been great advancements in the training of technologist that perform and the radiologists that interpret mammography.
Early detection remains a must if we wish to continue to improve the survival rate of breast cancer. To dismiss the value of mammograms is to turn a blind eye toward a disease that is predicted to be diagnosed in 232,670 new cases in 2014 in the United States alone (source: American Cancer Society). It is the second leading cause of cancer death in women and dismissing exams that can lead to earlier detection is putting more women at risk.
In the video below, Dr. Tabár provides more details about the flaws behind the the CNBSS study.