The Pipeline

Canadian study revives controversy over mammography screening


Rachel Bauch, Service Line Strategy Advisor

The global debate over breast cancer screening for women between the ages of 40 and 59 was revived early this year, when data released from a Canadian study concluded that “annual mammography in women aged 40 to 59 does not reduce mortality from breast cancer beyond that of physical examination or usual care when adjuvant therapy for breast cancer is freely available.” 

The basis for this debate is in part due to the difficulty in detecting lesions in younger women with denser breast tissue.


Mammography leads to concerns of over-diagnosis

The Canadian National Breast Screening Study (CNBSS) aimed to compare the incidence and mortality of breast cancer in women aged 40 to 59 who did or did not undergo mammography screening.

The CNBSS originally began in the 1980s, studying over 89,000 women, aged 40 to 59, randomized to mammography screening and control groups. The study evaluated the benefit of screening women aged 40 to 49 compared with usual care, and the risk benefit of adding mammography to breast physical examination in women aged 50 to 59. It was not deemed ethical to include a no screening arm for women aged 50 to 59.

The most recent update to the CNBSS includes data from a 25-year follow-up period. The study concluded that overall, 22% of invasive breast cancers detected in the mammography screening group were over-diagnosed. This represents one over-diagnosed breast cancer case for every 424 women who underwent mammography screening in the study.




Researchers warn against making generalizations

One limitation of this study is that the results of the most recent CNBSS should not be generalized to all countries. Yet, the researchers believe that in technically advanced countries, the results of the CNBSS support the views of some health leaders that providers should reassess the rationale for breast cancer screening by mammography.

Overall the CNBSS continues to cast doubt on the effectiveness of mammography for women 40 to 59.


ACR and SBI respond with disapproval

According to the American College of Radiology (ACR) and Society of Breast Imaging (SBI), the recent CNBSS is a misleading analysis. The ACR and SBI warn that the results from the CNBSS should not be used to create breast cancer screening policies as this would place a significant amount of women at increased risk of dying unnecessarily from breast cancer.

The CNBSS has created an even deeper rift between those who believe that screening mammography saves lives and those who are skeptical of its positive impact on women’s health. 


Conflicting recommendations confuse patients

This debate continues to fuel the conflicting information patients receive on screening mammography from their clinicians and various media outlets. While little information is currently available regarding whether this is decreasing screening volumes, anecdotal evidence indicates that screening volumes may be decreasing as a result. 

Health systems must work closely with their radiologists to develop a clear message to patients on the benefits and risks of mammography screening.


Controversy highlights need for better detection technologies

The global debate surrounding the routine use of mammography screening highlights the urgent need for technologies that can better detect breast cancer in the screening setting. New modalities such as digital breast tomosynthesis (DBT) and automated breast ultrasound (ABUS) aim to improve detection, while reducing callback rates.  

While these technologies are promising, further evidence is needed to quantify their impact and place them in the breast imaging pathway. Adopting these newer technologies geared towards dense-breasted women can likely help health systems differentiate their breast imaging programs, while also enhancing their breast screening programs. 

More on Breast Cancer Screening

Want more on mammography and other screening technologies? Check out these articles:

Tomo on the rise: DBT shows improvement in screening setting

In case you missed it: DBT shows improvement in screening setting

A brighter future for ABUS