Comparison of incident breast cancer cases in the largest national US tumor registries.
Authors: Plichta Jennifer Kay , Thomas Samantha M. , Record Sydney , Hyslop Terry , Hwang Eun-Sil Shelley , Greenup Rachel Adams 
Published: June 2023

6512 Background: National tumor registries, such as the NCDB (National Cancer Database) and SEER (Surveillance, Epidemiology, and End Results Program), have been used to explore numerous research questions related to trends in disease incidence, treatment patterns, and outcomes. However, some have criticized that they may not fully represent the general population. As such, we sought to compare the incident breast cancer cases in the NCDB and SEER to a national population cancer registry. Methods: All patients diagnosed with malignant or in situ breast cancer 2010-2019 were selected from the NCDB (Fall 2022 release) and SEER-22 (November 2021 release) and compared to breast cancer patient counts from the US Cancer Statistics Public Use Database (USCS, 2021 submission). Patient frequencies were summarized by age, sex, race/ethnicity, and year of diagnosis. Percent case coverage was estimated as the number of patients in the NCDB or SEER divided by the number of patients in the USCS. Chi-square tests were used to compare patient counts across data sources. Results: In total, the USCS database reported 3,047,509 patients diagnosed with breast cancer between 2010-2019, of which, 77.5% (N=2,362,477) were included in the NCDB and 46.0% (N=1,403,272) in SEER. Over time, case coverage steadily improved for the NCDB (72.8% in 2010 to 81.5% in 2019), while only a minor increase was observed in SEER (46.0% in 2010 to 46.6% in 2019). When compared to the USCS, case ascertainment was notably lower for individuals age ≥50 in both the NCDB and SEER (both p<0.001). The overwhelming majority of patients were captured by the NCDB (age <50: 81.7%; age ≥50: 76.6%) while SEER identified approximately half (age <50: 49.4%; age ≥50: 45.3%). Case ascertainment also varied significantly by patient sex across registries (both p<0.001). For male breast cancers, 84.1% were captured in the NCDB, only 77.5% of female patients were included. In contrast, case coverage in SEER was better for females than males (46.1% vs 43.5%). Notably, registries varied significantly by race/ethnicity (both p<0.001). Case coverage in the NCDB was highest for non-Hispanic White (78.2%), non-Hispanic Black (77.7%), and non-Hispanic Asian or Pacific Islander (72.5%) patients, and it was lowest for Hispanic (56.4%) and non-Hispanic American Indian/Alaska Native (41.1%). In SEER, case coverage was highest for non-Hispanic Asian or Pacific Islander (78.1%) and Hispanic (69.6%) patients, and it was considerably lower for all other subgroups (non-Hispanic Black 44.8%, non-Hispanic White 42.4%, and non-Hispanic American Indian/Alaska Native 36.6%). Conclusions: National US tumor registries provide data for a large sampling of breast cancer patients, and case coverage has improved over time. However, significant differences in case coverage were observed based on age, sex, and race/ethnicity, suggesting that analyses using these data sets should be interpreted with caution.