Abstract PO-153: Triple negative breast cancer (TNBC) in Indiana: A population-based cohort study from the Indiana Cancer Registry
Authors: Bales Casey L. , Shen Fei , Jiang Guanglong , Nurrenbern Walker , Flores Jaqueline , Schneider Bryan , McFarlane Tim 
Published: December 2020

Background: TNBC has a poor prognosis compared to estrogen receptor (ER) and HER2 positive breast cancer, yet its etiology is unclear. Despite having a low incidence of all breast cancers, Indiana (IN) has a diverse socioeconomic, racial, concentrate urban/rural makeup, and thus provides a perfect study population to explore the etiology of TNBC through investigating the occurrence based on the geographical and demographical incidences in the state. Methods: Cancer registry data from the State Department of Health was used to examine the incidence, characteristics, and distribution of TNBC across the state of Indiana. TNBC cases were identified as those with negative ER, progesterone (PR), and HER2 status; whereas controls were positive for any of the three receptors. During 2010-2015, 19,267 invasive breast cancer cases had receptor status available for this analysis.

Covariables such as age, tumor biology, and breast cancer subtypes were evaluated by multiple t-tests and chi-squared testing. To compare the occurrence of TNBC among different ages and races within a specific area, the 5-year Standard Incidence Ratio (SIR) was used and ratios over one signify the percentage above the expected number of cases. SIR was calculated by dividing observed cases by expected cases during the study period. To obtain the expected number of cases the highest NCI SEER all ages all race incidence rates 2000-2016 was used, as no state incidence rates for TNBC are available. Results: Indiana has 15% greater (p= 1.54E-13) incidence of TNBC compared to the nation. The age-adjusted incidence of TNBC broken down to the county level verified 59% of counties having rates above the national rate of 13.9. Nearly one third (28%) of TNBC incidence, were in Lake (Southeast of Chicago) and Marion (Indianapolis) counties. These are the most populated, urban, and racially diverse counties in IN. SIRs for both counties were remarkably higher than expected. Moreover, in Marion and Lake, the Black-specific SIR for TNBC was 1.4 (p=5E-6) and 1.7 (p=2.494E-8) while the Caucasian-specific SIR was 1.3 (p=1E-6) and 1.3 (p=9E-4). Analysis of specific zip codes within each county revealed clustered areas with extremely high SIRs, ranging from 2 to 238% above expected. Conclusion: Our results demonstrated significantly higher incidence rates of TNBC in Indiana. The highest age-adjusted incidence of TNBC was focused around urban, industrial, low income, heavily African American zip codes. This aligns with work by Downey et al which describes a highly significant 1.76 increased toxic concentration ratio exposure for Blacks compared to Whites in Indianapolis/Marion County (2007). Higher than expected ratios for both races implies that environmental exposures could be contributing to an increased incidence. This is the first study to show the geographical clustering of TNBC incidence, primarily around highly urban areas.

Citation Format: Casey L. Bales, Fei Shen, Guanglong Jiang, Walker Nurrenbern, Jaqueline Flores, Bryan Schneider, Tim McFarlane. Triple negative breast cancer (TNBC) in Indiana: A population-based cohort study from the Indiana Cancer Registry [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-153.