Primary tumor location impacts survival in colorectal cancer patients after primary resection: a population‑based propensity score matching cohort study.

Background: Right-sided colon cancers (R-CCs) are associated with worse outcomes compared to left-sided colon cancers (L-CCs). This study aimed to investigate whether a difference in survival existed among R-CC, L-CC, and rectal cancer (ReC) and subsequent liver metastasis. Methods: Data from the Surveillance, Epidemiology, and End Results (SEER) database for 2010-2015 was used to identify colorectal cancer (CRC) patients who underwent surgical resection of primary disease. Propensity score adjustment and Cox regression models were used to identify risk factors and prognostic factors of primary tumor location (PTL). Kaplan-Meier curve analysis and the log-rank test were used to evaluate overall survival (OS) of CRC patients. Results: Our results showed that among the 73,350 included patients, 49% were R-CC, 27.6% L-CC, and 23.1% ReC. Before propensity score matching (PSM), the OS of the R-CC group was significantly lower than that of the L-CC and ReC groups (P<0.05). However, the clinicopathological characteristics, including gender, tumor grade, tumor size, marital status, tumor (T) stage, node (N) stage, and carcinoembryonic antigen (CEA), were significantly unbalanced among the 3 groups (P<0.05). After 1:1 PSM, 8670 patients were effectively screened out in each group. The differences in clinicopathological characteristics among the 3 groups were significantly reduced, and baseline distribution characteristics such as gender, tumor size, and CEA were significantly improved after matching (P>0.05). Survival was higher in the left-side group when evaluated by tumor sidedness, and ReC patients had the highest median survival (114.3 months). Right-sided cancer patients had the worst prognosis in both PTL and sidedness analyses, with a median survival of 76.6 months. Among CRC patients with synchronous liver metastases, adjustment by inverse propensity weight and propensity score and analysis of OS yielded similar results and had more significant stratification results. Conclusions: In conclusion, R-CC has a worse survival prognosis compared to L-CC and ReC, and they are fundamentally different tumors that have distinct effects on CRC patients with liver metastases.