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Researchers Examine Benefits of DBT Screening

Researchers at Fox Chase Cancer Center in Philadelphia recently published a commentary examining clinical practices for breast cancer detection using traditional mammography vs digital breast tomosynthesis (DBT) on baseline and subsequent screenings. DBT, also called 3D mammography, can be used to identify early signs of breast cancer in women with or without early symptoms.

“The take-home point of this publication is that we’re now getting more information about specifically which women benefit from digital breast tomosynthesis over traditional mammography or digital 2D mammography,” says study author Catherine Tuite, MD, an associate professor of radiology and section chief for breast radiology in the department of diagnostic imaging at Fox Chase.

According to researchers, mammography remains the standard for breast cancer detection. However, although women who receive breast cancer screenings through mammography have an improved chance of surviving a breast cancer diagnosis, mammograms have limitations, such as false-positives and high recall rates.

Tuite says breast tissue density, which can only be determined by a mammogram, is a major factor in the efficacy of mammography. There are four categories of density; it is categorized as fatty, scattered fibroglandular, heterogeneous, and extremely dense. Tuite says the more glandular tissue a patient has, the whiter a mammogram appears. In those cases, it is more likely that breast cancer will be hidden in the dense breast tissue and not visible to a radiologist.

“The tomosynthesis mammogram has been thought to be better for finding abnormalities in dense breast tissue, but previous publications regarding that topic lump heterogeneous and extremely dense categories together and compare them to digital mammography,” Tuite says.

While it has been shown that all women benefit from DBT over digital mammogram at baseline screening, this study indicates that results of DBT in subsequent screenings differ according to individual breast density categories. 

“For women with scattered density and heterogeneously dense breasts—the two middle groups—those women benefit from decreased recalls and increased cancer detection with subsequent mammograms using tomosynthesis over a 2D mammogram,” Tuite says.

The data also indicate that DBT can decrease recalls in women with breast tissue categorized as fatty, she adds, but it does not necessarily increase cancer detection in those women. Additionally, women with extremely dense breast tissue don’t benefit from either decreased recalls or increased cancer detection in subsequent mammograms using DBT after baseline imaging.

“We’re not quite there, yet, but we’re working toward more personalized screening studies for each woman, depending on her risk profile,” Tuite says. “Breast density is an independent risk factor for breast cancer so now we’re taking that into consideration along with family history, gene mutations, or a host of other factors.”

— Source: Fox Chase Cancer Center

Study IDs Women Who Benefit Less From DBT

DBT improves cancer detection and reduces recalls, but women with extremely dense breasts seem not to fully realize that advantage. A recent comparison of two breast-screening technologies has found that, for most women, DBT is superior to digital mammography for cancer detection and reducing recall visits due to unclear or false findings. The study’s distinction, though, is in identifying women for whom DBT’s advantage is less. Previous evidence had suggested that DBT would generally benefit all women.

“DBT is improving screening outcomes for the vast majority of women getting screening mammography. Unfortunately, it does not seem to benefit the 10% of women who have extremely dense breasts and who already experience the poorest of mammography outcomes today,” says Kathryn Lowry, MD, an assistant professor of radiology at the University of Washington School of Medicine. Lowry and Yates Coley, PhD, an assistant investigator in biostatistics at Kaiser Permanente Washington Health Research Institute, were colead authors on the paper.

DBT was approved by the FDA in 2011, but clinicians did not have a corresponding medical billing code for it until 2015. Despite its recent emergence, several studies have associated DBT with better cancer detection and fewer recall visits than digital mammography, but few have been able to examine differences between subgroups of women.

In their research, the investigators analyzed more than 1.5 million breast exams from women ages 40 to 79, measuring cancers detected and patient recalls by age groups, breast densities, and baseline exam vs subsequent exams. They found that DBT is most beneficial for women undergoing their first screening mammogram, associating that group with the largest improvements in recall reduction and cancer detection. In subsequent exams, most women experience one or both of these benefits with DBT. But, for women whose breasts were categorized as “extremely dense,” DBT did not make a difference in how many cancers were found or how many recalls they had.

“This is a concern because this group of women is known to be at higher risk for cancer and higher risk for having cancers missed by mammography,” Lowry says.

Beyond that subgroup, DBT’s superior performance to digital mammography was broadly experienced, she adds. Importantly, most women with dense breasts are in the heterogeneously dense category, and these women had the largest boost in cancer detection with DBT.

The findings accrue to research being pursued by members of the Breast Cancer Surveillance Consortium, a US network of breast imaging registries. Coley conducted the analysis of data from the participating registries, which was pooled at Kaiser Permanente Washington.

“This study incorporated so much data and from sites that are geographically, racially, and ethnically diverse, and this allowed us to explore questions that other researchers have not,” Coley says.

“Our findings can help providers and patients better decide how to make decisions about screening mammography,” she adds. “If a provider only has access to one or two DBT machines, it will help them determine which patients should get priority with those. If a patient has to pay more out of pocket or drive several hours to reach a provider who offers DBT, this can help them know whether they’re likely to experience benefit.”

FDA data suggest that about two-thirds of US mammography facilities offer DBT. Insurance coverage, however, has lagged and is inconsistent across states.

Many women do not know the density of their breasts, Lowry says; the four categories each describe a different mix of glandular tissue, fibrous connective tissue, ducts, and fat. About one-half of all women have dense breasts, with a higher proportion of glandular and connective tissue; about 10% of all women have “extremely dense” breasts.

Nearly 40 states now mandate that women having mammograms receive some form of notification about the impact of breast density on breast cancer risk and detection of cancer. Language of these laws varies by state, and not all women are informed of their specific density category, Lowry says. For instance, a woman may be told she has “dense breasts” but not specifically told she is among the 10% of women whose breasts are extremely dense.

When DBT was introduced, “we hoped that it would benefit these women,” Lowry says, “but, unfortunately, this adds to the evidence that we still need to think about how to improve screening for this group.”

— Source: UW Medicine