Does where you live play an important role in cancer incidence in the U.S.?

Some studies have shown disproportionate cancer incidence burden in rural areas which may be attributable partly due to the use of 'rural' as a generic term implying homogeneity of risk/protective factors across wide geographic spans. Counties in SEER 18 registries (years 2001-2011) were classified by their Rural-Urban Continuum Code (RUCC) and aggregated into urban, adjacent rural, and non-adjacent rural and were also aggregated into 3 regions: North, South, and West. Two-way ANCOVA was performed with region and RUCC as factors with adjustment for rates of common risk factors obtained from the County Health Rankings (2013). RUCC has a significant effect on incidence rate in urban areas on breast (P =0.001) and prostate (P =0.009). Colorectal significantly varies by region (P<0.0001), and the effect of rurality significantly varies across regions with North highest (P=0.0005). Lung rates significantly vary across both region and RUCC (P<0.0001 and P=0.0001, respectively). The analysis shows that risk-adjusted cancer incidence varies significantly across regions. However, we also found that rural cancer incidence significantly varied across otherwise-similar rural areas implying that 'rural' is not a homogeneous classification.