Associations of subsite-specific colorectal cancer incidence rates and stage of disease at diagnosis with county-level poverty, by race and sex.

BACKGROUND: This study examined associations of subsite-specific colorectal cancer incidence rates and stage of the disease with county-level poverty.
METHODS: The 1998-2001 colorectal cancer incidence data, covering 75% of the United States population, were from 38 states and metropolitan areas. The county-level poverty data were categorized into 3 groups according to the percentage of the population below the poverty level in 1999: <10% (low-poverty), 10%-19% (middle-poverty), and >or=20% (high-poverty). Age-adjusted subsite-specific incidence rates (for all ages) and stage-specific incidence rates (for ages >or=50) were examined by race (whites and blacks), sex, and the county's poverty level. The differences in the incidence rates were examined using the 2-tailed z-statistic.
RESULTS: The incidence rates of proximal colon cancer were higher among white males (11% higher) and white females (15% higher) in the low-poverty than in the high-poverty counties. No differences across county poverty levels were observed among whites for distal colon and rectal cancers or among blacks for all the subsites. The late-to-early stage incidence rate ratios were higher in the high-poverty than in the low-poverty counties among white and black males for distal colon and rectal cancers, among white females for distal colon cancer, and among black females for rectal cancer. For proximal colon cancer, however, the late-to-early stage rate ratios were similar across all county poverty levels.
CONCLUSIONS: Higher incidence rates of proximal cancer were observed among white males and females in the low-poverty counties relative to the high-poverty counties. The higher late-to-early stage rate ratios in high-poverty than in low-poverty counties is observed for distal colon and rectal cancers, but not for proximal colon cancer.