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False-Negative Screening and Diagnostic Mammograms in the National Mammography Database From 2010 to 2022 | AJR Background: False-negative (FN) mammograms typically delay breast cancer diagnoses and may impact clinical outcomes. However, systematic evaluations of FN mammograms are challenging to conduct due to interval cancers' low incidence. Objective: To evaluate the rates of FN screening and diagnostic mammograms in the National Mammography Database (NMD), and to assess associations of FN rates with patient- and facility-level characteristics. Methods: This retrospective study included all screening and diagnostic mammograms in the NMD performed from January 1, 2010, to December 31, 2022. Patient- and facility-level factors were extracted from the NMD. FN mammograms were defined as those with a negative result in a patient with a tissue diagnosis of breast cancer within the subsequent 1 year. FN rates per 1000 examinations were computed. Separate multivariable analyses were performed to identify associations with FN results for screening and diagnostic examinations. Results: The analysis included 38,304,525 mammography examinations in 15,585,433 women (mean age, 58.8±11.7 years). Of 32,267,238 screening examinations, the FN rate was 1.9 (minimum, 0.7 in 2010; maximum, 2.5 from 2020 to 2022). Of 6,037,287 diagnostic examinations, the FN rate was 4.0 (minimum, 2.3 in 2010; maximum, 5.4 in 2020). In multivariable analysis for screening examinations, the likelihood of a FN examination was lower for race categories other than White (OR=0.30-0.95), higher for breast density categories other than almost entirely fatty breasts (OR=1.60-2.00), higher for women with personal (OR=3.69) or family (OR=1.29) history of breast cancer, and higher for academic or university-based facilities (OR=1.37); for diagnostic examinations, the likelihood of a FN examination was lower for race categories of Asian (OR=0.91) and Hawaiian (OR=0.77) and higher for a race category of Black (OR=1.12), lower for Hispanic patients (OR=0.70), higher for heterogeneously (OR=1.46) or extremely (OR=1.86) dense breasts, higher for women with personal (OR=7.82) or family (OR=1.31) history of breast cancer, and higher for academic or university-based facilities (OR=1.37). Conclusion: Rates of FN screening and diagnostic mammograms increased over time and showed significant associations with patient and facility characteristics. Clinical Impact: Exploration of the causes of the observed associations could inform quality assurance efforts to reduce the risk of delayed breast cancer diagnoses. https://ajronline.org/doi/10.2214/AJR.25.33636