Trends in colorectal incidence by anatomic subsite from 1985 to 2005: a population-based study

Abstract

Background: Conflicting results on the shift of right-left ratio in colon cancer incidence have been reported. We examine incidence trends by subsite in a population-based study.

Materials and methods: Colorectal cancer cases diagnosed in the 1985-2005 period were identified through the Tuscany Cancer Registry. Colon subsite was defined as proximal and distal; gender, age at diagnosis, histology, and stage were analyzed. Average annual incidence and age-specific rates according to subsite were calculated.

Results: A total of 21,160 colorectal cancer cases were extracted; in 18,311 cases, the subsite was identified: 6,916 rectal, 5,239 proximal, and 6,156 distal. A larger proportion of distal colon cancers presented as early stage when compared with proximal. Incidence of rectal and distal colon cancer remained stable, while proximal colon cancer incidence increased.

Conclusions: Proximal colon cancer incidence rate increased through the period. Temporal variations in the incidence rate by subsite could suggest different carcinogenic pathways of right- and left-sided colon cancer.