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Ultrasound Finds Cancers Missed by Mammogram in Dense Breasts

San Antonio—Results from a Connecticut study have some clinicians proclaiming that all women with dense breasts who have a negative mammogram should be offered an ultrasound. The study, presented at the 2014 San Antonio Breast Cancer Symposium (SABCS; abstract S5-01), found that ultrasound identified an additional 3.2 cancers per 1,000 women.

“It is time to think of a new paradigm of utilizing screening ultrasound,” said the lead author of the study Jean Weigert, MD, a radiologist and director of Breast Imaging at the Hospital of Central Connecticut, in New Britain.

Since October 2009, Connecticut law has required clinicians to use certain language when providing mammographic results to women with dense breasts (approximately 40%-50% of women). Clinicians are required to say, “Your mammogram demonstrates that you have dense breast tissue, which could hide small abnormalities, and you might benefit from supplementary screening tests, which can include a breast ultrasound screening or a breast [magnetic resonance imaging] examination, or both, depending on your individual risk factors.”

Connecticut is one of 19 states, to date, that mandate that clinicians include information on breast density when providing mammogram results to patients, according to Jafi Lipson, MD, assistant professor of radiology at Stanford University Medical Center, in Palo Alto, Calif. Additionally, Dr. Lipson said, “Insurance coverage for supplemental tests is now mandated [for patients with dense breasts] in four states, and there is federal legislation pending at this point.”

This flurry of legislation was spurred, in part, by a multicenter 3,000-patient study that demonstrated that adding a single, bilateral screening ultrasound to mammography detected an additional 4.2 cancers per 1,000 in women with dense breast tissue and a family history or prior history of breast cancer (JAMA 2008;299:2151-2163). This almost doubled the number of cancers found by mammography alone.

In the new study, researchers evaluated the effect of the new Connecticut law at two radiology practices with multiple sites in the state during the first four years after the legislation was enacted. Overall, 30% of women with dense breasts and a negative mammogram chose to have an ultrasound, and this rate was steady over the four years. “This may be due to lack of education and insurance issues,” said Dr. Weigert, who thought the rate should have been higher. “There are many high-deductible plans, and women do not want to pay for the test.”

The positive predictive value (PPV) of ultrasound improved over time, indicating that, as expected, there was a learning curve in determining which identified lesions needed to be followed and which needed to be biopsied (Table). By year 4, the PPV was 17.2%, with 3.2 additional cancers detected per 1,000 women. “The first three years, we were still doing a significant number of biopsies on patients with findings that we didn’t know whether they were positive or negative, but in the fourth year, there was a significant [improvement],” said Dr. Weigert.

Table. Positive Predictive Value of Ultrasound in Connecticut Practices Studied
Year PPV of Ultrasound, % Screening Mammogram Screening Ultrasound BIRADS 1 or 2 BIRADS 3 BIRADS 4 or 5 Positive Biopsy
1 7.1 30,679 2,706 2,377 174 151 11
2 6.1 32,500 3,351 3,000 168 180 11
3 8.1 32,230 4,128 3,819 168 148 13
4 17.2 27,937 3,331 2,889 358 53 11
BIRADS, Breast Imaging Reporting and Data System; BIRADS 1, negative; BIRADS 2, benign; BIRADS 3, probably benign; BIRADS 4, suspicious abnormality; BIRADS 5, highly suggestive malignancy; PPV, positive predictive value

The cancers detected were of all histologic grades but predominantly grade 2 and 3, hormone-positive and node-negative. Very few patients had risk factors other than dense breast tissue. Cancers were detected in patients who were in their mid-40s to mid-70s.

Although the study was limited in that it did not include a cost analysis, she pointed out that it is easier and less costly to treat a cancer if it is detected at an early stage, noting that in patients who returned for an ultrasound in a subsequent year, the cancers detected were extremely small, typically less than 1 cm.

A recent study estimated that supplemental ultrasonography screening for women with extremely dense breasts would cost $246,000 per quality-adjusted life-year gained (Ann Intern Med 2014 Dec 9. [Epub ahead of print]). This is well above $50,000, often touted as a reasonable threshold for cost-effective care (N Engl J Med 2014;371:796-797).

Dr. Lipson, who served as the discussant of the Connecticut study, pointed out that most of the PPV improvement in Dr. Weigert’s study was due to a shift of patients from a recommendation for biopsy to a recommendation for short-term follow-up, and this could be seen as a benefit or harm. “It’s not that the patient is returned to annual screening. She is kind of sucked into a vortex of short-term follow-up,” said Dr. Lipson.

Dr. Lipson also noted that none of the breast cancer ultrasound studies conducted so far have used a control group, and none have long-term follow-up. “The true clinical impact of finding these additional cancers is really unknown,” Dr. Lipson said. “Specifically,” she added, “would these additional cancers otherwise be detected at the next mammography screen while still small, node-negative, and at the early stage, and does the detection of these early cancers have an impact on mortality?”