Anatomical Distribution of Colon Cancer: A Retrospective 10-year Study to Evaluate Rightward Shift in Two Referral Hospitals in Iran

Background: In Iran, the incidence of colorectal cancer has been increasing over the last 25 years. Although left-sided colon cancers are still more common, several studies in recent years have shown a shift toward right colon. This rightward shift could have important clinical and healthcare consequences, as right-sided tumors generally have poorer prognoses compared to left-sided tumors and besides, are more likely to be missed in screening colonoscopy. Objectives: This retrospective study aimed at describing the demographic and clinicopathologic characteristics of patients with colon cancer based on tumor sidedness in two referral hospitals in Tehran. Methods: Data of the patients with colon cancer who had been treated from 2010 to 2020 in two referral hospitals in Tehran, Iran were retrospectively reviewed. Collected data included patients’ demographics, tumor histology and differentiation, tumor location, stage, and disease-free survival (DFS). Results: A total of 1535 cases entered the study including 849 (55.3%) males and 686 (44.7%) females with a mean age of 58.22 years (range: 22 - 89). Regarding the sidedness, 800 (52.1%) had left-sided and 735 (47.9%) had right-sided tumors. Although there were more cases of left-sided tumors compared to right-sided ones on total, there existed a trend toward shifting to the right side, which was statistically significant. There existed more cases of poorly differentiated tumors in the right side and besides, right-sided tumors had poorer DFS compared to the left-sided tumors (68.3% vs 78.3%). Conclusions: Left and right colon tumors differ in molecular mechanisms involved in tumorigenesis. These differences in epidemiological, molecular and histological parameters can have clinical implications. Tumor-sidedness should be acknowledged as an important epidemiological parameter with significant impacts on screening, tumorgenesis, response to treatment, and prognosis.