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

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.