Do mammograms “save lives”? Yes, but this is a more complicated question than you might have realized. You have probably heard me say that overall breast cancer has a great prognosis. For women with no spread of disease outside of her breast the five-year survival rate is 99%. With lymph nodes involved this drops to 85%. It is only when the cancer has spread elsewhere in the body that the survival rate drops to 27%.
Overall, breast cancer is a largely survivable diagnosis. This is great news for many of us since breast cancer is also common, affecting 1 in 8 women over her lifetime. But with a disease that most women survive, it is difficult to show that mammograms “save lives” and here are a few reasons why-
1. Mammograms often find precancerous or noninvasive disease. From my perspective as a physician and as a woman I cheer this diagnosis. We can intervene to reduce the chance of this patient ever developing invasive breast cancer, of ever needing chemotherapy, of ever having a potentially fatal diagnosis. The devil’s advocate would point out that not all women with precancerous or noninvasive disease will go on to develop invasive breast cancer. We do not know if this individual would have had invasive breast cancer in her future or not. We cannot definitively say that we “saved her life” from a diagnosis she might never have developed.
2. For women with invasive breast cancer the good prognosis also confounds our ability to judge the value of the mammogram. Earlier stages of diagnosis generally will require less aggressive treatment than later stages. Routine screening mammograms allow us to find more early stage cancers. For those early stage individuals who are fortunate enough to not need chemotherapy there is a real benefit to having her cancer identified early. Contrast this to a woman who did not have a mammogram and then was diagnosed at a later stage and needed chemo. These ladies will probably both survive their cancers, so did the mammogram “save” the life of the woman who was screened? Maybe not if she would have survived after a later diagnosis without mammograms, but it did save her from needing chemotherapy.
3. Unfortunately, some cancers are particularly aggressive. For a subset of women, an aggressive type of breast cancer is going to occur and it is going to grow quickly. Having had a normal screening mammogram 8 months prior did not predict or prevent her from having an advanced stage breast cancer before her next mammo is even due. In these cases, screening mammography might not have benefited her unless she happened to be due for the mammogram at precisely the time when her tumor began to grow.
These examples are NOT reasons to avoid mammograms, but they do explain some of the challenges when it comes to assessing the overall value of screening mammography. For these reasons, I believe the data used to generate mammography screening recommendations need to look at more complex endpoints than the overly simplified question of “do mammograms save lives?” I have seen the benefits of early detection by mammograms and will continue to advocate for screening mammography. In a future post I will try to sort out some of the conflicting recommendations regarding screening mammography.
