Spatial and spatio-temporal clustering of late stage diagnosed colorectal cancer cases in Houston, Texas for 1993-2005

Colorectal cancer (CRC) remains one of the top causes of cancer morbidity and mortality in the U.S. Although early detection and diagnosis lead to an increase in the survival rate, minorities and the underserved continue to have the worst outcomes. The objective of this study was to identify patterns of colorectal cancer incidence and late-stage diagnosis in Houston, Texas. Methods: Thirteen years of geocoded CRC data from the Texas Cancer Registry were attained for 592 census tracts encompassing the city of Houston. Community-dwelling adult cases, residing within the study area at the time of diagnosis, were selected for analysis (N=13,818). Results of previous spatial analyses indicated that many low income African American neighborhoods in Houston are at elevated risk of both excess incidence and late stage diagnosis of CRC. For this study, purely spatial Poisson probability models, adjusted for age and poverty, were created in SaTScanTMsoftware (version 7) to evaluate the effect of area level poverty on previously identified cluster patterns. Spatio-temporal analyses were then performed to determine if clustering was stable over the thirteen year study period. Results: Results indicate that poverty is associated with clustering of late stage CRC diagnosis across much of the study area, with the exception of the location of the primary cluster. Spatio-temporal analyses reveal a shift in the location of primary clusters, of both incidence and late stage diagnosis, from south central to northeast Houston during the study period. Discussion and Conclusions: Further research is warranted to identify factors other than poverty that may be associated with the primary cluster. The possible reasons for shifting of clustering of late-stage CRC diagnosis from one low income predominantly African American neighborhood in the early years of the study period to another in the latter years of the study period is under investigation.