Connected to my last post (and anticipated by my razor-sharp commenters), in this post I want to look at the pros and cons of routine screening mammography in women under age 50, drawing on the discussion of this subject in the multi-page “patient instructions” document I received from my primary care physician.
The aim of screening mammography is to get information about what’s going on in the breast tissue, detecting changes that are not apparent to the eye or to the touch. If some of these changes are the starts of cancer, the thought is that finding them sooner can only be better, allowing more time for treatments that remove the cancer or that slow its grown and arrest its spread to other parts of the body.
Having more information earlier, you’d figure, is bound to save lives. (Whether this conclusion is supported by the data is harder to discern, as Orac makes clear in this discussion of relevant research.)
But the information comes at a cost. Not only do mammograms require fancy (and expensive) equipment to capture the images, well-trained technicians to work with the patient to get the images, and well-trained physicians to interpret the images, but they expose the patient whose breasts are being imaged to low dose X-rays. Exposure to this sort of ionizing radiation can increase your risk of cancer.
So, right off the bat, it makes sense to have a screening policy that gets you the most useful information for the least risk and cost. Here’s how the patient information I was given lays out the thinking behind the risk/benefit balance my medical group favors:
Before menopause, breast tissue is generally denser, making it more difficult to detect cancer. Breast cancers in premenopausal women occur less frequently but are more aggressive than in postmenopausal women. The average time between detecting breast cancer on a mammogram and feeling the cancer on a physical examination is 1.25 years for women in their 40s and 3 years for women in their 50s.
First item to note: mammograms for younger women are likely to be less informative than mammograms for older women. This means that starting routine screening too early is likely to incur more cost and risk relative to the amount of information than mammogram offers.
However, if time is a crucial component in successfully treating breast cancer, the aggressiveness (on average) of such cancers in younger women may make the early detection offered by a mammogram a big benefit — at least for the (relatively small) number of younger women who develop breast cancer.
If the system were set up so you had to decide, as an individual, whether to start screening mammography before or after age 50, your decision might come down to your bet about whether you were more likely to be in the majority of your demographic group (for whom the costs and risks of a mammogram might seem excessive for the amount of useful information) or in the minority (for whom catching an aggressive cancer early would be a clear benefit that would outweigh the costs). People seem to come to this kind of personal risk-benefit analysis with very different levels of risk-aversion or risk-tolerance. (Also, there’s some question about whether most of us have any intuitive grasp of the probabilities in such situations.)
However, to the extent that most of us who are getting regular health care in the U.S. are doing it within the context of some kind of insurance, we aren’t generally making this call individually. We’re working within the framework of our health care provider’s policy, which usually tracks what insurance will cover.
Back to the patient instructions document:
There is no evidence that screening mammography in women younger than age 40 saves lives, and routine screening in women under age 40 is not recommended. Recommendations for women ages 40 to 49 remain somewhat controversial. The American Cancer Society and National Cancer Institute, which focus on preventing cancer deaths, recommend yearly screening mammograms for women 40 to 49 years of age. The U.S. Preventive Services Task Force and the American College of Physicians, which more broadly analyze the risks and benefits to the population being screened, do not recommend screening for this age group.
The reason for the different recommendations from different professional organizations stems largely from how each group weighs the importance of false positive and false negative screening results. A false negative mammogram is one that misses a breast cancer discovered by some other means, usually breast physical examination. A small number of missed breast cancers is unavoidable, which is why all women should also have careful breast exams and serial mammograms. A false positive mammogram is one that initially is reported as suspicious for cancer, but no breast cancer is confirmed. With mammograms, false results are more common before menopause. Among women ages 40 to 49 being screened annually, up to one-third will have a false positive result at some point, requiring additional mammograms and/or a biopsy that does not confirm breast cancer. This can cause anxiety, loss of work time and discomfort. Women planning to have screening mammography should be aware of the risks of false positive and false negative results and be prepared for further tests if indicated.
[The medical group from which I get my health care services] reviews the guidelines for screening mammography each year, and our own recommendations have evolved. We currently recommend that women ages 40 to 49 have an annual screening mammogram performed.
Here, I’m really impressed that the patient information about mammography not only acknowledges the differing recommendations for the 40-49 age group but also discusses the reasoning behind these differing recommendations. Medical professionals are treating women like grown-ups with the brain power to navigate complexity! It should happen more often.
As far as the logic of those competing recommendations — annual screening for women 40-49 versus no routine screening mammography until age 50 — the key difference seems to be whether preventing cancer deaths is the benefit to be secured, or whether something like maximizing the quality of a patient’s life (which includes a number of factors besides not dying from cancer) is the goal. I appreciate that this document acknowledges some of the additional costs you’re likely to rack up if your policy is total breast surveillance/zero tolerance of potential cancers. Because some mammograms, especially in younger women with denser breast tissue, are going to suggest problems where there are none, and establishing whether there’s cancer in the face of a suspicious mammogram could require:
- further mammography (with the attendant cost, discomfort, and exposure to ionizing radiation)
- a biopsy (with the attendant cost and discomfort)
- loss of work time (and/or need to find child care) to be available for these additional diagnostic procedures
- some amount of freaking out waiting to get the results to find out if you have cancer or it’s a false alarm
Screening an age group with a lower likelihood of breast cancers and with harder-to-image breast tissue seems likely to give more false alarms. The false alarms could provide a real hit to your quality of life, if you’re one of them.
On the other hand, an undetected breast cancer (which is, obviously, one you’re not treating, since you don’t know it’s there) could, in the fullness of time, provide its own hit to your quality of life. Indeed, that’s the major harm from a false negative: you may assume, on the basis of the mammogram, that there’s no problem. If you have insurance coverage that brings you in for a physical with your primary care physician every two years, that may mean two years until the next careful physical exam of your breasts. (Yes, regular breast self-exams are recommended, but a lot of women don’t do them regularly, or may not notice the kind of change that is supposed to be a sign to contact your primary care physician.) That could be two years in which a cancer escapes treatment.
My medical group’s policy has opted for the screening recommendation aimed at preventing cancer deaths, but they make it very clear in this patient information document that mammography does not yield perfect information. Sometimes a mammogram suggests a problem that isn’t really there, and sometimes a mammogram misses a problem that really is there. As well, my hunch is that women who are personally more inclined toward the risk/benefit analysis of the U.S. Preventive Services Task Force and the American College of Physicians can discuss this with their primary care physicians and opt out of routine screening until age 50.
Part of how I come to this hunch is the way the patient instructions discuss screening mammography for women 50 to 70:
Because cancers grow more slowly and are easier to detect in this age group, mammography may be performed at less frequent intervals, every one or two years. We currently recommend that women ages 50 to 70 undergo a screening mammogram every one to two years. Women in the following two categories will generally choose yearly mammograms:
Those with more concern about lowering the risk of breast cancer death and less concern about the effects of false negative and false positive tests.
Those at greater than average risk for breast cancer (discussed below).
In other words, the women in the 50-70 age group are given the relevant information and allowed to decide whether to get a mammogram every year or every two years on the basis of which benefits they prefer to maximize and which risks they prefer to minimize. Informed consent here includes choosing which surveillance strategy to pursue with respect to their breast health. Their agency is recognized.
I really like my health care providers.