Proximal shift of advanced adenomas in the large bowel--does it really exist?

During the last decades, the proximal shift in the distribution of colorectal carcinomas (CRCs) has been described. It is uncertain whether the shift is the result of actual changes in CRC incidence or reflects population aging. Most CRCs develop as a result of malignant progression of benign epithelial neoplasms--advanced adenomas (AA).

The aim of the study was to investigate whether the proximal shift of AA occurs over time.

Two databases were used. The first one (RETRO) included consecutive patients of the Department of Gastroenterology treated between the years 1981 and 1994. The secondone (Colonoscopy Screening Program--CSP) included asymptomatic participants of the colonoscopy screening program recruited between 2000 and 2004 from the Warsaw region. Only patients with AA who underwent total colonoscopy were included in the analysis. AA was defined as adenoma of 10 mm or more in diameter, with high-grade neoplasia, and villous or tubulovillous morphology, or any combination of the above features. The analysis was conducted using 2 different definitions of the proximal segment in the large intestine--either splenic flexure or the bend between the descending and sigmoid colon. To compare the distribution of AA, a multiple logistic regression model was used.

41 of 200 patients (20.5%) in RETRO and 122 of 430 patients (28.4%) in CSP group, respectively, were found to have AA located proximally to the splenic flexure. No proximal shift of AA was found after age and sex adjustment (P>0.1).

The risk of having proximal AA was similar in both groups. The results suggest the lack of proximal shift in the distribution of advanced colorectal adenomas.