Aims It has been described that colon cancer exhibits different characteristics depending
on whether it is located proximally or distally. However, differences based on location
have been less studied in preneoplastic lesions. The aim of the study is to evaluate
whether proximal and distal advanced adenomas (AA) present clinical, histological,
morphological, or molecular differences.
Methods A retrospective observational study that evaluates colonoscopies performed at our
center during the year 2022. We selected explorations where at least one advanced
adenoma was resected. The study variables were subsequently compared based on their
location proximal to the splenic flexure (right colon) or distal to it (left colon).
Advanced adenomas were defined as those larger than 10 mm, with high-grade dysplasia
(HGD), or intraepithelial carcinoma. Molecular differences were analyzed based on
alterations in the DNA repair system, which was evaluated through immunohistochemistry
techniques for MLH1, MSH2, MSH6 and PMS2 proteins.
Results Out of 4143 colonoscopies performed during the study period, at least one AA was
resected in 228 colonoscopies (5.5%), of which 141 (61.8%) were distal. The patient´s
mean age was 67.6±13.2 years, with a predominance of males (57.9%). When demographic
variables were compared, no differences were found in age, gender, smoking, or non-steroidal
anti-inflammatory drugs use. However, patients with proximal AA had a higher frequency
of previous polyp history (14.2% vs. 40.2%, p<0.001) and previous AA history (5.7%
vs. 26.4%, p<0.001). Regarding polyp characteristics, no differences were found in
size, but morphological differences were observed, with sessile (34% vs. 60.9%) or
flat polyps (2.1% vs. 17.2%, p<0.001) being more common in the right colon. Histologically,
there were also differences, with a higher presence of HGD in the right colon (29.8%
vs. 40.2%), but a higher percentage of intramucosal carcinoma in the distal location
(13.5% vs. 2.3%, p=0.011). Finally, immunohistochemical analysis of DNA repair proteins
showed nuclear positivity in all cases except for one proximal polyp [1]
[2]
[3].
Conclusions Mismatch repair status was not different between proximal and distal advanced adenomas.
However, they exhibit different clinical, morphological, and histological characteristics
which suggests that preneoplastic lesions may also have distinctive biological behaviors
depending on their location.
