This recent JAMA article (subscription required) carefully studies the role of adding ultrasound to mammography in breast cancer screening. They found that the combination picked up more cancers but also increased the false positives. In the parlance of clinical epidemiology, it increased sensitivity but decreased specificity.
Or as Homer Simpson would say: DUH!
It is not uncommon that the two co-vary in opposite directions. You can virtually manipulate the sensitivity and specificity of a test by carefully choosing your cutoffs for indicating the presence of absence of disease. The test ends up performing according to your needs. Our purpose in combining tests is to maximize both sensitivity and specificity. HIV is a case in point, since it is an over-sensitive antibody test (won't miss anyone) followed by an extremely specific confirmatory Western blot (won't wrongly diagnose anyone). Most labs won't report a positive antibody unless the Western blot is also positive.
I wish the results of the breast cancer study would have shown a reduction in false positives by the addition of ultrasound. This has always been my fervent hope whenever I have added an ultrasound to a mammography. The lesson of the report is that ultrasound doesn't help that much and must be used with caution and judgment.
Journal Watch reports a JAMA editorialist pointing out that
despite the high number of false-positives, what high-risk women "probably fear most is a late diagnosis." That, she continues, is "the real threat they want to be protected against, not false-positive diagnoses."Again I must say, DUH!
This study is meant to help guide us through the emotionally charged fear of breast cancer. It packs a huge punch for any woman even suspected of having the disease. On the other hand, we need to know the real (scientific= truth) value of doing a test. Perhaps the editorialist is saying that since it is an emotional matter, neither the data nor the truth matter, as long as we only detect more stuff, cancerous or not.
The original article is very detailed and a great read for those with an interest in how to crunch numbers to guide investigative decisions. The editorial set me off!
7 comments:
I belong to a bc support group and I could have told you that MRI's generate false positive.
I'm surprised insurance companies haven't put the lid on MRI's because it seems like 4/5 of the women in my online group who have an MRI have a benign biopsy. Most of these gals have already had breast cancer so they're hyper-vigilant about it all.
My wife's MRI was negative. That is tremendously reassuring, when it is negative. However, digital mammography raises false positives too, which we are worrying about now!
These tests are all useful, but making light of the inherent limitations of the technology is simply infuriating! Caution and judgment should be the basis of any action or medical recommendation.
All the more power to the support groups. They will keep us all in line! Wish I could be there.
To me, a false positive causing unnecessary biopsy is preferable to the possibility of a missed early diagnosis of breast cancer. When I hear the word "emotional" connected to a woman's decision to do anything, it sounds like a throw-back to the paternalistic theory that our hormones govern our decision making. In my opinion, a woman's fear of breast cancer is not based on emotion, but on the very real fact that if not caught early, she stands a great chance of dying from this terrible disease.
Emily, I agree wholeheartedly about the nature of anyone's decision in the face of false-positives. I'm not so sure about the emotionality being a throwback to paternalistic times. There is little value to add to the debate by throwing gender in. Perhaps it would help to know that prostate cancer screening with PSA has a far higher rate of false positivity than breast. It's emotional for men too.
but on the very real fact that if not caught early, she stands a great chance of dying from this terrible disease.
I think one of the problems here is that most women overestimate the power of early detection. Most women - over 70% - survive breast cancer even if it is detected later. Out of those who would've died without screening, 70% would still die even with screening (assuming mostly cited optimistic 30% reduction of mortality number). In absolute numbers this 30% mortality reduction translates into 1/500 chance of having one's life prolonged after 10 years of screening, and many consider this number overly optimistic. Now this is true for average risk women, for high-risk women the numbers may be different.
As to false positives, what most people don't realize is how common they are. 10% risk after the first mammogram, somewhat smaller risk after each subsequent one sounds small, but over 10 years, this number translates to almost 50% risk of having at least one false positive. About 1/4 of these false positives will end in biopsy. Then there is an issue of overdiagnosis...
These false positve can have real risks. A biopsy carries small risk; but even anxiety after false positives may have a real effect on one's blood pressure or one's risk of heart desease. When you screen a lot of people, this extra risk may matter however small it may be. Given that heart desease is so much more common than breast cancer, it is really difficult to have a study where this effect would reach statistical significance. For someone at high risk of breast cancer the anxiety caused by fear of a missed breast cancer may be higher than that of the false positive, but what about someone who is at average risk of breast cancer but at high risk of heart desease? What if this someone has a type of personality that gets fast heart beat, high blood pressure for weeks just because of a false positive?
This is why false positives are an important concern - they can cause real phisical harm; and given how common they are and how small the probability of an individual benefitting from testing is, it is really difficult to say which number is greater. The studies showed that screening reduces breast cancer mortality. The effect on all cause mortality is much more difficult to determine, and thus it was never demonstrated.
Doctor, I didn't throw gender into my comment, the thread is about female specific breast cancer.
You twice used the word "emotional"
regarding a woman's decision to be tested for BC. What did you mean when you wrote:
"...the emotionally charged fear of breast cancer."
"Since it is an emotional matter, neither the data nor the truth matter..."
I am a breast cancer patient, and all I know is that I don't want to leave one stone unturned in the fight against this disease. Is that emotional? Or is it resoluteness.
I think I understand. Some people believe that emotion is a bad attribute in a human being or perhaps a sign of weakness. I'm not sure I believe that. All decisions are colored by emotion at some level. It may be best to acknowledge the role of emotion in any decision, health care or otherwise, and take that into account as you try to figure out the best thing to do.
But there are no right or wrong decisions in health care, nor should there be judgment about the right way to make a decision.
Hopefully, in the face of cancer, most physicians provide the data, help guide the logic and support any decision you make!
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