Colorectal cancer incidence and survival by sub-site and stage of diagnosis: a population-based study at the advent of national screening

The location and staging of a colorectal cancer (CRC) determine prognosis and choice of treatment. We examined the sub-site, sex, and stage distribution for CRC in Ireland for patients diagnosed in the period immediately prior to the implementation of a national screening programme.

The incidence of CRC during 2010–2012 averaged 1021 females and 1424 males per year. While the overall incidence rate of CRC was static during 1994–2012, this masked a significant increase in the rate of proximal colon tumours (+1.3 % per year), a decreases in the rate of tumours of overlapping/colon NOS (−2.2 % per year), and no change in the rates of cancers of the distal colon and rectosigmoid junction (RSJ)/rectum. Proximal tumours occurred more frequently in females (F vs. M, 38 vs. 29 %), in older persons and increased over time. Compared to distal colon tumours, proximal colon [RR risk ratio 1.08, 95 % CI (1.05, 1.10)] and RSJ/rectum tumours [RR 1.08 (1.05, 1.11)] were more likely to be diagnosed at late stage. The proportion of late-stage tumours increased steadily over five diagnosis periods [e.g., 1994–1997 (51 %) vs. 2010–2012 (57 %), RR 1.12 (1.08, 1.16)]. Cancer survival improved over four diagnosis periods.

There was a distal-to-proximal shift and a trend towards diagnosis at late stage during 1994–2012. Some reversal of this trend is expected following the implementation of a national screening programme.