By Elaine Schattner M.D.|September 30th, 2010
It’s been nearly a year since we “learned” about the false positives issue, and still there’s hardly any data published on this much-maligned cost of breast cancer screening by mammography.
From the U.S. Preventive Services Task Force November 2009 paper in the Annals, on the lack of information on the incidence of FP’s:
“Published data on false-positive and false-negative mammography results, additional imaging, and biopsies that reflect current practices in the United States are limited. The probability of a false-positive screening mammography result was estimated at 0.9% to 6.5% in a meta-analysis of studies of sensitivity and specificity of mammography published 10 years ago <ref. 38>. The cumulative risk for false-positive mammography results has been reported as 21% to 49% after 10 mammography examinations for women in general <39–41>, and up to 56% for women aged 40 to 49 years (41)…
False positives happen in mammography when a woman has an abnormal result that looks like it might be breast cancer, but upon a further workup – which might involve another, more expert radiologist taking a look, or a sonogram, or an MRI, or even a breast biopsy, but in the end the problem turns out not to be breast cancer.
Why is it so hard to ascertain how often false positives occur?
1. The rate of false positive mammograms is, most likely, declining (i.e. the number is in flux).
Reduced errors would result from two factors: improved methods, such as by adaptation of digital mammography, and by more careful application of extant technology due to progressive compliance with the FDA’s Mammography Quality Standards Act and Program.
2. There’s no precise definition of what constitutes a false positive in mammography, and what isn’t. As I’ve suggested previously, finding a pre-malignant condition like LCIS or an early-stage malignancy like DCIS should not be “counted” as a false positive. If over-treatment occurs, that reflects an error in clinical decision-making rather than in mammography, per se.
3. The false positive rate varies among radiologists and medical centers. That’s because a radiologist who spends her days doing nothing but reading mammograms and breast sonograms will, overall, have a lower FP rate than a general radiologist who also handles hip fracture films and MRIs of the brain.
What are financial costs of false positives? I’m not aware of any new data on this.
How can we reduce the costs of false positives in mammography? My suggestions:
1. Radiologists should be well-trained and carefully-credentialed. As in surgery and other fields in medicine, the physician’s skills and experience affects the probable outcome.
2. Avoid doing breast biopsies in an operating room whenever possible. A fine needle aspirate or core needle biopsy, performed under local anesthesia, is almost always sufficient for diagnosis and less costly.
3. Thinking for the future: Maybe, one good application of Telemedicine would be in sharing digital mammography images, so that no matter where a woman lives, her test could be checked by a radiologist working in a central cancer center and who specializes in breast imaging.
4. Do the procedure every other year for women of average risk for breast cancer (rather than annually). Quite a few theoretical calculations of mammography costs “stack” the purported costs by assuming the procedure is done every year, but there’s no data to support such frequency.
In sum, there’s every reason to think the rate of false positives in screening mammography is falling and that costs from errors will diminish in the future.
Many, if not all, of the costs attributed to false positives will be reduced by advances in technology, better training of radiologists, and education of physicians (oncologists, surgeons, primary care physicians) who recommend the procedure and make decisions based on the results.