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Colorectal cancer incidence in the US is declining rapidly overall but, curiously, is increasing among young adults say researchers, while provisional Irish figures suggest there is no evidence of a decline in incidence rates of colon or rectal cancer in Ireland for the 20-39 age group. Furthermore, provisional figures indicate a significant increase in rectal cancer incidence for males in the 20-39 age group. Overall, declines in incidence rates of colon or rectal cancer in Ireland during the period 1994-2014 appear be confined to older age groups (55+), according to the preliminary data compiled by the National Cancer Registry Ireland (NCRI).

The latest US analysis by Rebecca Siegel and colleagues on “Colorectal Cancer Incidence Patterns in the United States, 1974–2013” says incidence rates for colon cancer have generally declined since the mid 1980s, and rectal cancer since at least 1974, in age groups of older than 55 years. The increase in incidence rates highlighted for the younger adult age groups in the US is prompting ongoing debate as researchers seek answers for current trends.

However, these preliminary Irish figures are not directly comparable with US rates in the analysis published recently in the Journal of the National Cancer Institute, as a different population standard is used for Irish calculations. Evidence of declining rates of colon and rectal cancer in Ireland for the 55+ age-group, are statistically significant for males and while non-significant for females, trends appear similar to those in males, according to the provisional NCRI figures.

Some evidence of a decline in the incidence rates of colon cancer in Ireland for the 40-54 age-group is seen, and is statistically significant for females while there are non-significant but similar trends for males. No trends in rectal cancer incidence rates for males aged 40-54 has emerged, but there is some evidence of an increase – not statistically significant – for females in that age-group.