Mammogram? 50 Years Of Data And Decision Aids To Help You Think Through

A mammogram image, with arrow in upper left pointing to cancer

A mammogram image, with arrow in upper left pointing to cancer

Any procedure that involves sandwiching your naked breast between hard glass plates is personal. Very. But it’s becoming ever more clear that getting a mammogram also holds an element of personal decision. Medical authorities put out broad guidelines, but then you and your doctor can customize them, based in part on your own breast cancer risk and preferences.

How? Before we get into that, a paper just out in the Journal of the American Medical Association takes a sweeping look at a half century of mammogram data, and offers this big picture: mammograms do save lives, “but those benefits are not enormous,” said Dr. Nancy Keating of Brigham and Women’s Hospital and Harvard Medical School, the paper’s co-author. While the potential harms — that a woman will undergo cancer treatment for a tumor that never would have actually harmed her — have tended to be underestimated.

Here, Dr. Keating lays out the mammogram numbers that I found most helpful:

“If we take 10,000 women who are at average risk at age 40, over the course of ten years about 190 will be diagnosed with breast cancer. Most of these women will do well and would have done well regardless of screening. About five of those 10,000 women will have their life saved by the mammogram. Another 30 of those women will die regardless of the mammogram because unforutunately some breast cancers are so aggressive that they’re destined to be deadly despite the mammogram.

So there is benefit, five out of 10,000 women have their lives saved, but there are also these harms. One harm is false positives and unnecessary biopsies,: Of 10,000 women, about 6,000 will have at least one false positive. At this point, I say to patients, ‘You should expect that you’ll have some false positives, and don’t worry when they call you back.’ The over-diagnosis harm, we estimate: about 36 of those 190 cancers that were diagnosed could be over-diagnosed, and so those women will be treated — because we can’t currently tell the difference between the cancers we need to worry about and those that might not be so concerning, so we treat them all the same. So those women are then subjected to the harms of treatment without gaining any benefits.

So how to customize? How do you help create your own risk-benefit analysis? I asked the Informed Medical Decisions Foundation for helpful tools, and they suggested three:

The National Cancer Institute’s Breast Cancer Risk Assessment Tool

Public Health Agency of Canada Mammography Decision Aid

Healthwise

And for a bit more background, Dr. Keating discussed mammogram issues with co-host Anthony Brooks on Radio Boston, including these highlights:

On the questions Dr. Keating sought to answer in her review:
Dr. Nancy Keating: “First, what are the benefits of screening mammography? Second, what are mammography’s chief harms? Third, following from the U.S. Preventative Services Task Force recommendations that we should individualize decisions about mammograms, what information is out there about how to do that? And then fourth, what do we know about how to support women and their physicians in making the right decision for that patient?”

On the answers:
NK: “For the benefits, overall, 40 to 50 years worth of randomized control trials do suggest that there are benefits to screening mammography in decreasing the likelihood that a woman will die of breast cancer. But those benefits are not enormous. Overall, we estimate about a 19 percent reduction in the risk of breast cancer, that varies from about 15 percent for women in their 40s and 50s to about 30 percent for women in their 60s. But the important thing with the benefit is it also depends a lot on a woman’s individual risk for breast cancer. If your risk is low, the likelihood that you will benefit is actually quite small.”

On over-diagnosis as a result of mammograms:
NK: “In the last couple years, we’ve really begun to better appreciate the extent of this harm, though I will say that the research that allows us to quantify the amount of over-diagnosis associated with mammography is quite complex, but basically when we do screening, and particularly when we do mammography, we identify cancers and we now feel pretty confident that some of the cancers we diagnose are cancers that would have never become clinically evident in a woman’s lifetime. There are two reasons for this. One is that the cancer may just be very slow-growing or it may even regress and not progress. The other is that a woman might actually die of something else before the cancer would become clinically evident.”

On how we create a more individualized approach to help women make the right decision:
NK: “We still don’t have all the tools we need for this, but the first step to do this is to help a woman understand what her risk of being diagnosed with breast cancer is. There are not perfect tools yet for this, but probably the best one we have is something called the Breast Cancer Risk Tool, which is made available to the public by the National Cancer Institute. You can go online and you can plug in your risk factors — information about family history, when you started menstruating, when you had your first baby, how many children you’ve had, and whether you’ve had previous breast biopsies and then that will give you an estimate of your likelihood of being diagnosed with breast cancer in the next five years compared with the average woman. So if your risk is higher than average, then because your benefit depends on your risk, you’re more likely to benefit.

Ultimately, there’s no totally simple answer. “We need to be more aware of the limits of this test,” Dr. Keating said. “Mammograms are not perfect tests.”

But at least you can get a better sense of your odds.

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