Women With Extremely Dense Breast Tissue May Not Benefit From 3-D Mammography

Compared with digital mammography (DM), digital breast tomosynthesis (DBT), also called 3-dimensional mammography, has been proven superior at effectively detecting breast cancer and leading to fewer recall visits, but more information is needed for how subgroups of women with different breast densities benefit from the screening method, especially those classified as having extremely dense breast tissue.

A woman’s breast density is based on a mix of her glandular tissue, fibrous connective tissue, ducts, and fat, and there are 4 categories:

• Almost entirely fatty
• Scattered fibroglandular density
• Hetergeneously dense
• Extremely dense

"Our findings can help providers and patients better decide how to make decisions about screening mammography," said Yates Coley, PhD, an assistant investigator in biostatistics at Kaiser Permanente Washington Health Research Institute, and the study’s co-lead author, in a statement announcing the study findings. "If a provider only has access to 1 or 2 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."

Their comparative effectiveness, Health Insurance Portability and Accountability Act—compliant study, published online today in JAMA Network Open, investigated the outcomes of DM and DBT as they were used for routine breast cancer screening, collecting results on age, baseline vs subsequent screening round, and breast density category. Data were gathered from 46 Breast Cancer Surveillance Consortium (BCSC) facilities on women aged 40 to 79 years, all with no history of breast cancer, mastectomy, or augmentation, who had a screening mammography between January 2010 and April 2018.

During the study period, DMs were performed more than 4 times as much as DBT: 1,273,492 vs 310,587. Breast Imaging Reporting and Data System (BI-RADS) categories ranging from 0 (incomplete, needs additional imaging evaluation) to 5 (highly suspicious for malignancy) were utilized to classify screening outcomes and define screening recall rates, with recall visits being defined as “exams with initial BI-RADS assessment of 0, 3 [probably benign], 4 [suspicious for malignancy], or 5.”

Overall, compared with DM, an adjusted analysis showed that per 1000 baseline exams among women 50 to 59 years, DBT improved screening recall visits by resulting in 15.4% fewer such visits (241 vs 204; relative risk [RR], 0.84; 95% CI, 0.73-0.98) and a higher cancer detection rate (5.9 vs 8.8; RR, 1.50; 95% CI, 1.10-2.08). Seventy-five percent of the cancers detected were invasive.

Similar results, also per 1000 exams, for DBT over DM were seen among same-age women with heterogeneously dense breasts who had additional breast exams:

• Recall visits decreased: 102 vs 93 (RR, 0.91; 95% CI, 0.84-0.98)
• Cancer detection rate rose: 3.7 vs 5.3 (RR, 1.42; 95% CI, 1.23-1.64)

There were no changes in the cancer detection rates for women 40 to 49 years who had scattered fibroglandular breast density and women 50 to 79 years who had almost entirely fatty-tissue breast density. However, recall visit rates did decrease from 240 to 215 (RR, 0.90, 95% CI, 0.80-1.01) for those 40 to 49 years and from 219 to 178 for those 60 to 79 years (RR, 0.80; 95% CI, 0.69-0.95) following subsequent exams.

The group of women who did not benefit from DBT over DM was those who have extremely dense breasts. No improvements were seen in decreased recall visits scheduled or a higher cancer detection rate.

The authors noted that DBT often involves patients having to foot the bill for the extra costs of the procedure because of “inconsistent insurance coverage” and that knowing whether they can benefit from it beforehand can help to inform their decision-making process. Legislation that applies to notifying women with dense breasts—of the 4 categories above, this applies to heterogeneously dense and extremely dense breast tissue—has already been passed in 38 states, “and in 2019 a federal bill was passed directing the FDA to develop national standards for density notification in mammography reports,” they noted.

“Our study is unique in its ability to estimate DBT performance by screening round, age group, and density categories given our large sample size,” the authors concluded. “Our findings suggest that density should likely not be used as a criterion to triage use of DBT for routine screening in settings where DBT is not universally available, as has been reported in physician surveys.

They believe that additional research and data are needed to examine if potential future legislation and clinical guidelines could be tailored to benefit women with extremely dense breasts, by focusing specifically on the risk reduction gains this group can achieve through supplemental screening.

Reference

Lowry KP, Coley RY, Miglioretti DL, et al. Comparison of screening performance of digital breast tomosynthesis vs. digital mammography in community practice by patient age, screening round, and breast density. JAMA Network Open. Published online July 28, 2020. doi:10.1001/jamanetworkopen.2020.11792