Purpose: The false negative (FN) rate of screening mammography is an important audit metric that identifies interval cancers, which are known to have worse outcomes. Current FN rates are confounded by interval cancers identified on supplemental screening modalities for intermediate and high-risk patients, termed asymptomatic FN cancers. Few studies make this distinction, limiting the applicability of standard benchmarks to programs providing supplemental screening. This study evaluates characteristics of FN cancers, including determination of symptomatic and asymptomatic FN rates, within a robust supplemental screening program.
Materials and Methods: Screening mammogram audit data from a single academic institution from July 1, 2018 to June 30, 2022 was retrospectively reviewed. Patients receiving a normal assessment and subsequent diagnosis of breast cancer within one year were analyzed to determine patient and tumor characteristics and method of detection. Supplemental screening volumes and mammographic audit metrics of the institution’s breast program were obtained.
Results: Ninety-seven FN cancers were identified in 81,302 screening mammograms during the four-year period, comprised of 46 (47%) symptomatic and 51 (53%) asymptomatic cases. The overall FN rate was 1.19/1000 screens, with a symptomatic FN rate of 0.57/1000 and asymptomatic FN rate of 0.63/1000. More symptomatic FN cases (18/46, 39%) had a personal history of breast malignancy than asymptomatic FN cases (11/51, 22%). Of the remaining 28/46 (61%) patients with symptomatic FN cancers, 12/28 (43%) had a Tyrer-Cuzick score >20%. Thirty-three (72%) patients with symptomatic FN cancers would have qualified for, though were not undergoing, supplemental screening based on risk status or breast density. Symptomatic FN cancers were larger at diagnosis (mean size 2.4cm vs. 1.4cm, p-value 0.01) and 14 (30%) remained mammographically occult at the time of diagnosis. MRI detected the majority (31/51, 61%) of asymptomatic FN cancers.
Conclusion: A robust supplemental screening program allows for symptomatic FN rates to fall below historic benchmarks. New FN benchmarks are needed for programs offering supplemental screening to compare audit and outcome metrics for asymptomatic and symptomatic FN cancers. Most patients with symptomatic FN cancers were at higher-than-average risk for breast cancer and underutilized available supplemental screening. This study underscores the importance of supplemental modalities for reducing symptomatic FN cancers, which have worse patient outcomes.
Clinical Relevance Statement: Current recommendations for risk assessment by age 25 and breast density notification will result in increased utilization of supplemental screening. This will require reassessment of screening benchmarks, including division of FN cancers into symptomatic and asymptomatic categories in order to identify opportunities for improved patient outcomes.
