Media are abuzz after the publication in the British Medical Journal on February 11, 2014, of the results of one of the largest randomized trials of mammography, which sought to determine whether screening mammography reduced death rates from breast cancer. In this longitudinal study, researchers randomly assigned nearly 90,000 Canadian women ages 40 to 59 years to receive regular mammograms plus breast exams or breast exams alone. The main outcome measure was deaths from breast cancer. Participants were followed for incident breast cancers for up to 25 years.
You can read the entire manuscript entitled Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial through the British Medical Journal website. The results showed that not only did screening mammography not reduce overall mortality from breast cancer; it actually resulted in overdiagnosis of tumors that did not require treatment.
What does that mean? Cancer is an unusual disease. Some of us could be walking around with a cancer in our body that never grows (and thus poses no threat to our health) or it will grow so slowly that it will never require any treatment. Some of us may even have a cancer that eventually shrinks or disappears on its own without any intervention. If we don’t undergo a screening test, we never know we have it. However, once a cancer is detected through a test such as mammography, it can’t be ignored. The results of the Canadian National Breast Screening Study showed that 22%, or approximately 1 in 5 cancers, that were detected through mammography and treated actually did not require treatment because they did not pose a threat to the woman’s health.
Keep in mind that this is just one study. Other clinical trials have found that screening mammography does reduce the death rate from breast cancer, and that makes it even more confusing for women and their healthcare providers to decide if and when to undergo mammography. Adding to the confusion are other breast imaging modalities being offered to women, such as tomosynthesis, or 3D mammography, and thermography. At this time, we don’t have enough evidence to know whether these techniques will improve cancer detection compared with traditional mammography or if they will ultimately save lives.
The mammography debate will continue, that’s for sure. For now, we would advise women to discuss their concerns openly with their physicians and review the evidence before undergoing any procedure. The goal is for everyone to be able to make an informed decision that will improve health outcomes and not lead to harm.