Why are there so many guidelines for screening mammograms?
I am frequently asked “Why are there so many guidelines for screening mammograms? Can’t anyone agree?” Currently there are three major organizations that recommend different guidelines for screening mammography. The American College of Radiology recommends screening at age 40 every year regardless of risk factors. The USPSTF states that women can wait until age 50 and receive a screening mammogram every other year instead of yearly, and women aged 40-49 should discuss with their doctor to determine if mammography is right for them. And the American Cancer Society has a hybrid guideline, stating women should start screening at age 45 and receive a screening mammogram every year until age 55, and then switch to every other year. WOW! No wonder there is so much confusion.
In the Information Age, and with increased access to the internet, the old model of the doctor telling their patient exactly what to do, without asking for the patient’s input is outdated. Hence, many of the guidelines emphasize that screening decisions should be made after a discussion between the patient and her healthcare provider. All the guidelines actually agree on certain points. But they differ on where they draw the line of benefits versus risks in terms of making routine recommendations.
One of the most important points where the guidelines all agree is that MAMMOGRAMS WORK and that MAMMOGRAMS SAVE LIVES. They all agree that “Yearly screening mammography starting at age 40 saves the most lives.”
It all comes down to where the individual guidelines place the proven benefit of saving more lives versus the risks of mammography- mainly the risk of a false positive result and over-diagnosis or overtreatment of cancers that may not actually be harmful. The good news is that no one is really worried about radiation risks using today’s mammography technology.
Breast cancer becomes more common as women age, so some guidelines place emphasis on screening starting at age 50, leaving the decade of women aged 40-49 to the individual woman’s decision after discussion with her healthcare provider. Nevertheless, it is important to know that 1 in 6 women diagnosed with breast cancer are diagnosed in the 40’s, and 75% of those cancers are diagnosed in women with no significant family history or special risk factors.
Some guidelines stress the risks of anxiety and unnecessary treatment associated with a “false positive” exam is a reason to not issue a blanket recommendation for screening all women every year from age 40 on. The term “false positive” means that the initial screening mammogram was called abnormal, which happens for about 1 in 10 women. The more mammograms a woman has over her life, the more likely she is, from a pure probability standpoint, to have a study called abnormal at some point (even if she is normal and does not have cancer). Therefore, some guidelines emphasize this risk, and say it is ok to have a mammogram every other year instead of every year, or that it is ok to wait until age 50 to start to screen instead of age 40. However, skipping to every other year instead of yearly mammograms will mean that some of the lives that could be saved by screening are lost. And, for the large majority of women who are called back for an abnormal mammogram, they simply need extra mammographic
pictures or perhaps an ultrasound before being cleared completely. Only about 1-2 in 100 women coming for a screening mammogram will end up needing a small procedure called a needle biopsy.
The other main risk discussed by most guidelines is over-diagnosis. Over-diagnosis refers to a cancer that is diagnosed from the mammogram that would have never have grown or spread in a way that would prove fatal to the patient if it had been left alone. The easiest way to think about this is imaging finding a small 2mm slowly growing cancer in a 100 year old woman, where the patient may die from other reasons besides the cancer. However, the true amount of over-diagnosis, based on autopsy studies of invasive breast cancer, is approximately 1 in 100 cancers. More importantly, at present, science does not have the ability to determine which cancers may confidently be left alone and followed, versus those which need standard treatment. Additionally, the frequency or age of starting screening mammography does not affect the rates of over-diagnosis and so this risk should not affect the screening guidelines.
Mammograms are far from a perfect test! Some cancers hide- even on the best performed and most expertly interpreted mammogram. This occurs more commonly in women with dense breasts, but can occur in any woman. Any focal symptom or lump should always be brought to the attention of the provider even if a woman has had a recent normal mammogram. Mammograms do use x-ray, which is a source of radiation, and this fact frightens some women. However, the amount of radiation is tiny, and in women of screening age, the dose of a mammogram is essentially nothing to worry about.
Most women, when aware of these facts, will choose to start screening every year beginning at age 40. A woman should always discuss health care decisions with her provider, and of course, should feel free to choose the course of action that is most appropriate to her. But, these facts need to be conveyed to all women as they decide which guidelines they will follow. If a woman does not have all the information, she isn’t empowered to make an informed decision.