As I write this, I still haven’t decided if I am going to get a mammogram at 40, or if I will wait until 50. I thought perhaps you might want to come on this journey with me as you might be struggling with a similar decision, confused by the changes in guidelines, or just questioning the benefit of mammograms in general. Breast cancer is the leading cause of cancer death in women and mammography has been shown to save lives, so it seems it should be a simple decision. However, there are some risks that come with pursuing a mammogram including; false-positive findings which can lead to anxiety and affect quality of life; false-positive biopsies; false-negative findings; false reassurance; overdiagnosis; overtreatment; and radiation exposure. To better understand the scale of benefits vs risks for screening starting at 50 years old, check out this graphic from NPR.
“The decision to start regular, biennial screening mammography before the age of 50 years should be an individual one and take patient context into account, including the patient's values regarding specific benefits and harms.” The reasoning behind this is that there is at least moderate certainty that the net benefit of screening is small.
This guideline is different from the recommendation of many other organizations including the American Cancer Society, the American Medical Association, and the American College of Obstetrics and Gynecology, which recommend that annual mammogram screening begin at 40 years old.
This article is a great summary about this debate. The bottom line is that overall there is more agreement than disagreement. There is agreement that starting screening in the 40’s does save lives. The USPSTF simply states that this decision on when to start screening should be an individual one and starting screening at 40 shouldn’t be an automatic decision. The other organizations emphasize the importance of starting screening at 40 for everyone.
So, how am I going to decide what to do next. I do have an engineering background so the numbers really are important to me, so let me lay out some statistics. Let’s start with the number needed to treat (see my blog about number needed to treat for more background on this). David Newman, author at thennt.com states that with mammography screening there was no reduction in breast cancer death, that 1 in 2 were harmed by a false positive and 1 in 5 were harmed by unneccesary surgery over the course of 10 years. He then goes onto explain that it’s difficult to tease out the number of lives saved with mammography because the overall number of deaths from breast cancer is a lower proportion of all deaths.
The USPSTF says that the net benefit of starting mamograms at 40 rather than 50 is small. What exactly is this small net benefit? This study found that starting screening at 40 vs 50 reduced mortality by an additional 3% (overall reducing death from breast cancer by 19% vs 16% if starting at 50 years old). Another way of looking at this is for every 1000 women who start screening at 40 vs 50, 0.7 extra lives will be saved (assuming they do mammograms every 2 years until 74). So what is the harm done in saving this extra 0.7 of a person? It means that 470 more women will have false positive results and 33 women will have unnecessary biopsies.
Looking at these numbers makes me understand why the USPSTF felt the need to push women to discuss whether to start screening at 40 vs 50. Two issues that concern me the most are the exposure to radiation and the chance of getting needless chemotherapy or radiation. I am personally less afraid about the false positive tests and needless biopsies, however if getting a mammogram is going to increase my risk of cancer (through radiation exposure) or expose me to needless aggressive treatments, I will think twice.
Overall the amount of radiation from a screening mammogram is quite low. To get some perspective on this it helps to understand that we are all exposed to radiation every day on this earth from cosmic rays and radon gas (on the order of 3 millisieverts every year). A mammogram exposes you to only 0.4mSv of radiation. This article from cancer.org gives a great overview of this. Most expert organizations advise that overall the benefit of mammograms far exceeds the small risk of increasing cancer related to radiation exposure.
How about my other concern -- overdiagnosis -- which leads to chemotherapy and radiation when it’s not necessary? This is related to the idea that many people who have cancer die from non-cancer causes. However, once cancer is diagnosed, it’s very difficult to tease out which cancers are going to shorten lifespan and which are not, so we treat all diagnoses of cancer the same. This table shows the numbers we have, they say that up to 104 women may be overdiagnosed while up to 16 lives will be saved (for every 10,000 women screening between 40 and 50). This doesn’t really help me because they don’t even have a sense of the lower range, meaning it could be 0 women are overdiagnosed and 16 are saved.
I do think the decision to pursue more frequent screening should take into account the baseline risks for breast cancer. The challenge is finding a meaningful screening tool that can guide you clearly on the decision and, for now, there isn’t a perfect one. The Breast Cancer Risk Assessment Tool is easily accessible and can give a basic sense of one’s risk in comparison to the general population. However, this tool was developed based on studies of only white and black women and may not be applicable to other races. Further, this tool isn’t meant for those with a family history of two or more people with breast cancer. There are more sophisticated models for those with a significant family history, but they are not easily accessible.
After all of this research, I have decided that I am going to start with screening mammograms when I am 40. I am personally comfortable with the risks and think that the lives saved in screening starting at 40 is worth it for me.
I hope that this information has helped you reflect on what makes sense for you in regards to screening mammograms so you can decide when you want to start.