The pros and cons of screening mammography: reading my 'patient instructions'.

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.

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Exposure to this sort of ionizing radiation can increase your risk of cancer.

I must take strong issue with this statement (although it was a very minor comment and doesn't affect the thrust of your post). There is no evidence that this kind of dose increases risk.

There might be unidentified subpopulations who are at increased risk; for example, carriers of ataxia telangiecstasia *might* have additional radiosensitivity when compared to the population.

Family history can cause a gal to blow all that out of the water.

It's my guess you don't have any because you're reading all the info with a detached attitude. If you have a mother/sister/aunt whose had breast cancer that goes out the window.

There doesn't seem to be consensus around the idea that mammography before age 50 saves lives. This rather extensive article at Women to Women (Christiane Northrup's original medical practice in Maine), at which breast expert Dixie Mills ( practices, seems to say that it's unclear (study results vary) as to whether mammograms for women 40-49 actually prevent deaths:

I can't help but agree with her hope that "in the near future there will be a simpler, better test like blood or urine for breast cancer. If a woman turns up positive, she could then go on to have a diagnostic mammogram, ultrasound or MRI."

On one hand, I thought that we were supposed to try to separate ourselves from our emotions when making decisions - we all have emotions and should expect them to affect us, but the emotions don't negate or mitigate the consequences of our actions, so it seems reasonable to minimize their effect on decision-making. Knowing someone who has breast cancer or other bad diseases increases our awareness of the costs involved in having the disease, but it doesn't necessarily increase one's own risk. The presence of family history should raise the risks of breast cancer substantially, and that might justify preemptive testing by itself.

On the other hand, I don't really know where to begin evaluating risks and benefits. Without my life, I have nothing, but doing nothing with it is not only a risk as well, it isn't possible, and so I have to take risks and thus don't (or can't) treat my life as if it has infinite value. How much more my life is worth than other things is inherently hard to evaluate - I can't put a number on it with any precision. The probabilities of events can be quantified effectively (although, in this case, the data aren't included), but without the ability to quantify the values of the desired outcomes, it makes it hard to discuss the actual risks. Not all things that count can be counted, I'm aware, but then the task seems to be evaluating the magnitudes and values of emotions and outcomes without real measures of them.

By Robert Bird (not verified) on 23 Jul 2008 #permalink

Mister Troll, does the risk from the ionizing radiation just relate to the dose of the particular procedure, or does the risk get (a little bit) greater with each additional exposure?

AnnR, you're quite right that I am approaching the procedure and the information about the procedure as someone with no family history of breast cancer, and that definitely influences how I weigh the risks and benefits. (The patient instructions do note, however, "Increasing age is the greatest risk factor for breast cancer, even more important than a family history of breast cancer." So, in 10 or 20 years my outlook may also be quite different.)

Robert, I'm not sure it's always possible to make a totally rational (non-emotional) decision in the face of imperfect information (about the present and the future) and hard-to-quantify considerations that matter to us. Given that this is the case, I'm impressed that my health care providers are working to empower patients to participate fully in making the decisions that will affect their own lives.

I have two lumps in my right breast. I can't even remember what they are called. (not fibrocystic). They have a 50% chance of turning into cancer at 'some point' so I get mamograms every 6 months and biopsies every year to monitor them.

It bothers my surgeon dramatically when she sees changes in them, and huge relief on her face when they are exactly as they were at last mamogram.

Last summer, there were changes... not only that, but one was found in my left breast which was statistically not likely at all. (exept that I'm on immunosuppressants I reminded her ...oh, yeah, ok, that's probably it)

Detatched? only way to be. If it happens, I'll deal with it. They could remain benign for 40 years! They could turn malignant next year. I cannot worry about them at all.

If I did, I'd go insane ...absolutely insane.

My docs worry about them for me, that's what they are there for. I stay on top of the appointments and insist that the techs do the job they are supposed to do when it is time for appts ... other than that ... the six months between appts ... my mind is clear of what is going on in there.

Emotions are facts in and of themselves, even if they're not clear interpretations of factual evidence. If I become so worried about breast cancer that I lose sleep over it even in the absence of risks or symptoms, then maybe an earlier mammogram is worth the peace of mind. (Maybe getting counseling for health anxiety is also worth it, but that's just another response to the same fact.)

I got my first mammogram at 30 and had them every 3 to 5 years for a while, then every 2, and now yearly. I have a few factors that might raise my risk of breast cancer, and one or two that might lower it. For a while it was a source of intense anxiety, and even now I get nervous when mammogram time rolls around, but I do get them.

Incidentally, I've never found mammograms to be painful. They do pinch a bit, but that part doesn't bother me. Also, the equipment designs are getting better, and I've noticed a distinct decline in the pinch factor between my first mammograms and my most recent ones.

By Julie Stahlhut (not verified) on 23 Jul 2008 #permalink

There seems to be a tendency for techs to try for somewhat less compression. This is good news and bad news. It hurts less, with less after pain. But if this mamo is being compared to your last which was high compression, the lower compression image WILL show differences--and guess what? They'll send you a letter to come back for "further studies", but "nothing to worry about".

Ya, right. So for the 3 weeks or so till you can get the appt. and time from work, etc. to coincide, you worry.

Now I just insist that my primary write the order for full compression the first time.

Thanks for bloggin on all this.

By Super Sally (not verified) on 23 Jul 2008 #permalink

"razor-sharp' is one interpretation. The other is that at least one of us is highly predictable...

I think one of the most interesting things you learn in public health is the costs and prevalance of False Positives (aka false alarms- you test positive for a condition you don't really have).

The last lecture I went to about a national breast cancer screening progam (if I can remember this correctly) indicated that you observed about 200-300 mammography false positives for every single women who was successfuly treated for breast cancer. Now that's the whole of the program aged 50 up. In woman aged 40-50 the figure will be much higher because the prevalence of cancer is much lower and the screening technology doesn't work as well even when cancer is present.

So is the emotional and physical harm caused by perhaps ?300-1000? false alarms worth saving that one person? Faced with that particular woman almost nobody would disagree. However, those resources could be much better spent elsewhere to save more than one person and at substantially lower risk.

It seems to me that many of the screening decisions that are made are based more on emotion or politics than what might be best for women's health overall. Of course that ignores somewhat a person's right to choose. But then people often make poor decisions with regard to their health - why would screening decisions be any different? Some people are of course more than capable but many are not.

I'd rather not end on a negative note. So the lecturer at that screening lecture also noted that false alarms can, oddly, also have positive effects for the women. Whilst the emotional unrest (and sometimes physical harm) can be seen close to the event if you go back to these women much later they sometimes view their experience positively and now value their lives as more precious than they had before. So the false positive might actually have improved their quality of life. A surprising idea that I hadn't actually heard before.

I've also heard (but don't have data to point you to) that the incidence of breast cancer in younger women is rising.

So it's worth noting that screening in younger women will be more effective if the disease is more common than has been historically noted.

If the president of the the United States was a woman in her forties, you can bet she'd be having annual mammograms.

But then if the US president were a woman in her 40s she would probably be doing a lot of night and/or extended work hours and she'd be at increased risk for breast cancer (Megdal et al, European Journal of Cancer 2005). Thus it might well be worth it in her case even putting aside the political issue.

I've had one mammogram during my 40s because it was more or less forced on me. I have dodged all the recommedations since then (my mammogram showed nothing suspicious). I'm about to be 48 and I have, and will be, telling my doctors that they can keep their mammogram recommendations until I turn 50. I decided this after listening to a lecture for grad students given by an epidemiology professor from UC Berkeley. I found it on iTunes.

The best evidence is that risk from ionizing radiation is similar to most other harmful agents: a little bit doesn't hurt you at all, but a lot will.

The dose from a mammogram falls into the "little" bit category (a fraction of the total natural radiation dose you would receive throughout a year). There's simply no evidence that it increases risk. (The *regulations* assume it does, but that's a different story.)

The last lecture I went to about a national breast cancer screening progam (if I can remember this correctly) indicated that you observed about 200-300 mammography false positives for every single women who was successfuly treated for breast cancer.

This suggests a great strategy for a quack. First, the quack uses advertising to convince people with positive mammograms to come get his quack treatment. Then, when further tests indicate no cancer (which will occur most of the time), the quack takes credit for 'curing' the cancer. I bet dozens of quacks are already doing this.

I may be naive or stupid, but I didn't think it was at all clear what the dose-response curve for ionizing radiation - a lot had suggested a "hockey-stick" curve, where there is a threshhold for damage, and others suggested that the curve was linear with no such threshhold.

What is the evidence for the former?

By Robert Bird (not verified) on 24 Jul 2008 #permalink

Re: Ionizing Radiation

The evidence is strong that the dose-response curve is linear at very high levels of radiation (Chernobyl, Hiroshima, et al).

But when you look at lower levels of radiation, several studies have shown that populations that receive slightly more radiation are actually slightly healthier. Now, this could be because people who live up in the mountains get more exercise than us city folk, or because the doctors that were evaluating health treated all the problems they found, or because small amounts of radiation are actually beneficial, or some combination of the three. (The first two are quite likely - I'm not so sure about the third.)

Government regulations and anti-nuclear activists tend to assume the worst-case scenario - that the effects of low levels of radiation can be extrapolated linearly from the effects of high levels of radiation. Even if that's true, the levels you'll get from medical equipment are far below anything that's measurable.

One risk of mammograms that hasn't been addressed in the article or the handout and that doctors often "forget" to mention is that of overdiagnosis and overtreatment. Overdiagnosis and overtreatment refers to detection of very slow growing or even indolent cancers that are so slow growing (or not growing at all or may even regress) that they wouldn't have spread in a person's lifetime if remained undetected. But since there is at present no way to distinguish those non-threatening tumors from the faster growing ones, they are treated when detected, and the treatment may cause complications.

Contrary to popular belief simply detecting a cancer early doesn't always make a difference. Cancers spread at different speeds. Some are very aggressive and will kill anyway regardless of how early they are detected as they tend to appear between screenings, and spread before screening can detect them or even microscopically from the start. Some grow slow enough that mammograms can detect them in time, and they indeed may spread before they can be detected in any other way. In case of this type of tumors mammograms can indeed save lives. Then there are those that grow so slowly that they are still perfectly curable when detected later e.g. during breast exam. And then there are those that wouldn't spread within one's lifetime if remained undetected.

Now some real statistics. It is often mention that mammograms reduce mortality from breast cancer by 30%. But this is a relative number (if I don't go into the ocean I'll reduce my mortality from shark bite by 100%) and has to be taken in the context of one's absolute risk of dying from breast cancer within say next 10 years. The figure of "1 in 8 women will get breast cancer" refers to one's cumulative life time risk if every woman lives until the age of 85; an individual woman's risk of getting breast cancer within next 10 years is much smaller. And then there is a fact that most women nowadays survive breast cancer even if it is detected later.

Better statistics is number needed to screen or how many women needs to be screened for, for example, 10 years for one woman to benefit. Here is this statistics for 50-something women and it is based on pretty optimistic review of data: out of 1000 women in their 50s who are screened for 10 years, 2 fewer will die from breast cancer. During the same 10 years, anywhere between 25 and 50% of women will have at least one false positive (number is smaller in Europe where they have biennial screening and greater in Europe; also American radiologists are afraid of lawsuits so they have higher rate of false positives). Around 1 in 4 of these false positives will end in biopsy. The number needed to screen is about twice as high for women in their 40s and the number of false positives is much higher as well.

As to overdiagnosis, it is difficult to estimate as the estimates range from 5% to 50% of all mammogram-detected cancers. The consensus estimate from Cochrane is about 30%. A paper published last year in British Medical Journal looked at the results of Malmo trial. Their estimate was 10%, but as replies from other researches in the Rapid Responses section of the paper showed, their math was flowed. The corrected number from one of the researchers was 25% or 1/4 of all screen-detected cancers representing overdiagnosis.

BTW - I am in my 40s, I had some mammograms in my early 40s, but after learning about the statistics I choose not to have them for now. I have not made a decision about whether or not I'll do them when I am 50: on the one hand there is a small (1/500) chance that it'll prolong my life. There is some additional chance that it'll reduce the need for more aggressive treatment or save my breast. But on the other hand, there is a higher risk of being diagnosed with breast cancer to begin with (because of overdiagnosis), and the greater overall risk of mastectomy (again, because of overdiagnosis). Then there are all these false positives; my risk of heart desease and the anxiety and rise in blood pressure that would accompany it.