Trends in colorectal cancer incidence by subsite in Osaka, Japan.

To date, the time trends of left-to-right shift of colorectal cancer incidence have been reported in Western countries. In the present study, we calculated the average annual number of colorectal cancer incidence and the age-adjusted colorectal rates, and examined the change of subsite distribution using the data from the Osaka Cancer Registry between 1974 and 2003. Mucosal carcinoma cases were excluded from the analyses. The proportions of right colon cancer among all colorectal cancer cases were consistently increased; from 21.5% in 1974-78 to 25.6% in 1999-2003 among men, and from 28.2% in 1974-78 to 36.8% in 1999-2003 among women. The age-adjusted incidence rates of right colon cancer among men and women recently levelled off, while the rates of left colon and rectal cancers showed a declining trend. Among women, right colon cancer was more common in the elderly than in the young. The change of subsite distribution seemed to be associated with population aging, changes of life style and the development of total colonoscopy. Careful monitoring is necessary to confirm these findings.