Does the Addition of MRI Help in Breast Cancer Detection in Women with Low Breast Tissue Density in Two Canadian Population-based High-Risk Breast Screening Programs?

Purpose To compare incremental cancer detection rate (ICDR) by breast tissue density (BTD) and determine whether breast MRI adds diagnostic value in high-risk individuals with low-density breast tissue. Materials and Methods This retrospective review included 10 233 screening breast MRI examinations performed between 2012 and 2022. For each examination, the Breast Imaging Reporting and Data System BTD category was recorded. Patient charts were reviewed to identify patients diagnosed with breast cancer (BC) during the screening period. The nearest mammograms were reviewed to assess whether cancers were also visible at mammography. Results Among 10 233 female individuals screened, 91 cancers were detected (cancer detection rate [CDR] = 8.90 per 1000 examinations), with no evidence of a difference across BTD categories (<i>P</i> = .39). By BTD category, seven cancers (7.7%) were in category A, 34 (37.4%) in B, 40 (44.0%) in C, and 10 (11.0%) in D. Among 90 BCs detected at MRI, only 18 (20.0%) had a corresponding abnormality identified on the nearest screening mammogram. Of the 872 MRI examinations in individuals with category A BTD, six of seven cancers (85.7%) were detected at MRI alone and one (14.3%) was detected at both mammography and MRI. No evidence of a difference in incremental CDR was found across BTD categories (A = 6.9 per 1000 examinations; B = 5.9 per 1000; C = 8.3 per 1000; D = 7.5 per 1000; <i>P</i> > .50). Conclusion In high-risk individuals with low-density breasts (category A BTD), supplemental screening with breast MRI remained necessary despite improved mammographic sensitivity. <b>Keywords:</b> Mammography, MRI, Breast, Primary Neoplasms, Screening © RSNA, 2025 <i>Supplemental material is available for this article.</i>