Proximal vs. distal colon cancer location: a subset analysis of the Minnesota colon cancer control study.

Background: Several patient and tumor characteristics impact the prognosis of non-metastatic colon cancer. Among those, tumor location is believed to be a significant factor, as proximal lesions are associated with lower overall survival (OS) in modern cohorts. We aimed to validate these findings in a cohort of patients from the Minnesota Colon Cancer Control Study who underwent curative colectomy.

Methods: From 1976 to 1992, 46,551 patients aged 50-80 years were randomized to usual care, annual, or biennial screening with fecal occult blood testing (FOBT). Positive FOBT was followed by colonoscopy. We analyzed participants whose colonoscopy revealed colon adenocarcinoma to estimate the impact of tumor laterality on survival after adjustment for demographic and clinicopathologic characteristics. Proximal tumors were defined as those between the cecum and the splenic flexure.

Results: Of 1,486 patients, 796 met inclusion criteria; 57% had proximal cancers. After adjustment, there was no significant difference between proximal and distal tumors in disease-specific mortality [subdistribution hazard ratio (SHR) =0.94, 95% confidence interval (CI): 0.70-1.3], but proximal tumors had lower rates of death from any cause [hazard ratio (HR) =0.9, 95% CI: 0.77-1.00].

Conclusions: Although lacking granular data, these findings from the pre-modern chemotherapy era raise questions about the generalizability of the association between side of origin and prognosis identified in contemporary, treatment-based trials.