Analysis of clinicopathological features and prognosis of mesenteric versus anti-mesenteric rectal cancer: a single-center retrospective cohort study.

Background: The mesorectal and anti-mesorectal sides of the rectum differ considerably in embryonic origin, blood supply, lymphatic distribution, and anatomical relations. Tumor location (mesenteric vs. anti-mesenteric) may therefore influence tumor biology and clinical outcomes. This study aimed to evaluate the impact of axial tumor location on clinicopathological features and prognosis in rectal cancer using preoperative high-resolution pelvic MRI. Methods: We retrospectively reviewed 380 rectal cancer patients who underwent radical resection between January 2017 and July 2023. Based on preoperative MRI axial images, tumors were classified by their deepest point of invasion relative to the rectal lumen: the mesenteric side group (3-9 o'clock, posterior/posterolateral walls, n=213) and the anti-mesenteric side group (9-3 o'clock, anterior/anterolateral walls, n=167). Demographic, clinicopathological, surgical, and survival data were compared between groups. Results: Among the 380 patients, 213 were assigned to the mesenteric side tumor group and 167 to the anti-mesenteric side tumor group. Baseline characteristics, including age, gender, BMI, TNM stage, MRF status, EMVI, and vascular/nerve invasion, did not differ significantly between two groups (all P > 0.05). With a median follow-up of 56 months, the 3-year local recurrence-free survival (LRFS) rate was significantly lower in the anti-mesenteric group than in the mesenteric group (91.6% vs. 97.1%, P = 0.029). No significant differences were observed in 3-year disease-free survival (83.2% vs. 82.1%, P = 0.832) or overall survival (85.6% vs. 81.7%, P = 0.501) between the two groups. Multivariable Cox regression analysis identified age (HR = 1.043, P = 0.002), surgical procedure (APR vs. LAR, HR = 1.967, P = 0.022), pathological T stage (HR = 2.800, P = 0.023), and pathological N stage (HR = 3.683, P < 0.001) as independent prognostic factors for overall survival. Pathological N stage was the sole independent predictor for disease-free survival (HR = 3.088, P < 0.001). Although axial location was not an independent predictor of overall or disease-free survival (P > 0.05), it was significantly associated with LRFS (anti-mesenteric vs. mesenteric: HR = 2.684, 95% CI: 1.126-6.398, P = 0.026) along with pathological N stage (HR = 3.960, 95% CI: 1.316-11.919, P = 0.014).These findings suggest that anti-mesenteric tumor location is an independent predictor of increased local recurrence risk, providing valuable information for surgical planning and postoperative surveillance beyond conventional staging. Conclusion: Anti-mesenteric rectal tumors are associated with a higher risk of local recurrence, likely due to complex local anatomy and surgical challenges. While pathological N stage, pathological T stage, age, and surgical procedure remain primary independent prognostic factors for survival outcomes, preoperative MRI assessment of axial location provides valuable supplemental information that may help stratify local recurrence risk, refine surgical planning, and optimize postoperative monitoring.