Exploratory analysis of the spatial distribution of adult glioma age-adjusted county incidence rates, Nebraska Medicine, 2009-2019.

Background: Central nervous system (CNS) cancers including gliomas have low incidence but high mortality. The age-adjusted incidence rate for CNS cancers is higher in Nebraska than nationally. This exploratory study was motivated by glioma patient inquiries about possible clustering of cases within the state to see if more in-depth investigation was warranted.

Methods: Using electronic health records from Nebraska Medicine, we identified Nebraska adult (age ≥19) glioma patients diagnosed between January 1, 2009 and November 1, 2019. Patient residential addresses were geocoded, mapped, and combined with annual US Census data to compute age-adjusted incidence rates (AAIR) at the county level. Counties with fewer than five cases were excluded to protect patient identity. ArcGIS software was used for geocoding and mapping.

Results: Of the 285 cases included in the analysis, 53.2% were geocoded with exact match and the remainder were processed manually. Cases occurred in 47 of the 93 counties. After data suppression, 11 counties (228 cases) visually clustered in eastern and central Nebraska with AAIR ranging from 0.85 to 5.66 per 100 000.

Conclusions: Many counties in the state were excluded from analysis of this rare cancer due to the small number of cases leading to unstable rates and the need to suppress data to protect patient privacy. However, this preliminary study suggests that glioma incidence is highest in central and eastern Nebraska. Next steps include analysis of state cancer registry data to ensure more complete case ascertainment.