A study published this week in the Journal of the American Medical Association makes the case that more breast cancers will be found in high-risk women screened with both mammogram and ultrasound than in those screened with mammography alone. Finding more breast cancer early, when it is more reliably curable at best, more treatable at worst, is clearly a good thing.

The study, conducted in almost 3000 women, also revealed that the net benefit of combination testing was fairly low, between 1 and 7 additional cancers detected early out of 1000 high-risk women screened. But let's face it- even that low yield is very important if it makes a life or death difference. And if you happen to be, or know and love, the one woman who benefits- the case for ultrasound will be strong indeed!

The trouble here is that screening has a dark side, too. The more disease you find that's there, the more likely you are to find what looks like it could be disease...but isn't. The measure used in Medicine that best reflects the trade-off between true positives (abnormal test result and disease truly present) and false positives (abnormal test result and disease truly absent) is "positive predictive value" (PPV). This measure is the percentage of positive test results that are correct.

The PPV for mammogram alone in the new study was about 22%; roughly 1 in 5 abnormal mammograms was associated with an actual breast cancer. The PPV for combination testing with mammogram and ultrasound was half that, or 11%. In other words, only 1 in 10 abnormal screens meant cancer was present.

(For those interested in a more detailed discussion of these trade-offs in screening, read my article, "Medical Decisions Between Scylla and Charybdis," posted on 3/2/08.)

As for breast cancer screening with ultrasound, my take is this: it's fine, as long as there is a robust plan in place to deal immediately with potential false positives. I have been through the anxiety of a false positive breast cancer test with my wife, my mother, AND my sister. Sleep was lost on all occasions! So minimally, we need a system in place so that follow-up testing is immediate when a screening test is abnormal. That, at least, limits the number of nights lost to sleepless worry.

If we plan appropriately for the inevitable false positive, we can put technology to optimal use, and minimize the number of cancers that get by us, while also minimizing the anxiety we cause by raising false alarms.

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