Colorectal cancer incidence and mortality in Texas 1990-1992: a comparison of rural classifications

Although cancer incidence and mortality rates are known to be higher in urban populations, more unstaged tumors and later staged cancer are diagnosed in rural populations. Most investigators have used a dichotomous definition of urban and rural in studying these populations, and they have not considered whether a more detailed categorization of rural areas could influence their findings. The objective of this study was to evaluate colorectal cancer incidence and mortality rates in Texas from 1990 to 1992 by using a dichotomous definition (Metropolitan Area vs. Nonmetropolitan Area [MA/non-MA]) and two more detailed rural classifications (the Rural-Urban Continuum Code [RUCC] and the Urban Influence Code [UIC]). Cancer data were obtained from the Texas Cancer Registry for 1990 to 1992 and supplemented with data from the Texas State Department of Vital Statistics (mortality), the US Census Bureau (age, gender, race) and the Area Resource File (rural and urban definitions). Incidence and mortality rates, age-adjusted to the 1970 US standard population, were calculated for non-Hispanic White, African American, and Hispanic males and females. Results revealed a nonlinear relationship between rural category and colorectal cancer incidence or mortality for all races. Applying the MA definition yielded rates in the middle of the ranges obtained with using RUCC or UIC classifications and most closely reflected the result for non-Hispanic Whites using the more detailed scales. Our results suggest that a dichotomous definition of rural and urban may mask important variation in colorectal cancer incidence and mortality rates within rural areas.