Background: Incidence and mortality from cancer of the colon and rectum have declined in recent years in the United States and California, but reasons for the decline are unknown.
Methods: Age-adjusted site-specific and stage-specific incidence rates were calculated for approximately 9,000 cases of in situ cancer and 120,000 cases of invasive cancer of the colon and rectum diagnosed between 1988 and 1996 among California residents and reported to the California Cancer Registry. Trends in incidence over time were measured using the estimated annual percent change.
Results: Among non-Hispanic whites there was a decline in all sites and stages, but the decrease was most pronounced for rates of in situ and regional/distant tumors in the rectum and sigmoid which declined by about 4 to 7% a year. For tumors in the proximal colon, the decrease was statistically significant only for regional/distant tumors which declined about 2% a year. Among blacks, there was an approximately 7% annual decline in the incidence of regional/distant tumors of the rectum in women and a nearly 3% a year decrease in regional/distant tumors of the proximal colon in men. The decline in rates for Hispanics and Asian/Pacific Islanders was smaller and less consistent than for non-Hispanic whites.
Conclusions: The results confirm a overall decline in all stages of cancer of the colon and rectum in California, particularly among non-Hispanic white men and women. The decrease was most pronounced for tumors in the rectum and sigmoid colon and may be attributable to screening.
Copyright 2000 American Health Foundation and Academic Press.