OBJECTIVES : Right-sided colon cancer (RSCC) is projected to be a disease with a different entity to the left sided colon cancer (LSCC). We examined the relationship between colon cancer and 5-year mortality by using propensity score matching.

METHODS : Adult patients (age>18) with colon cancer were identified from the Surveillance, Epidemiology, and End Results (SEER) database (2004–2014). RSCC and LSCC were identified using International Classification of Diseases, Oncology, Third Revision, diagnosis codes (ICD-O-3). RSCC included: 18.0 (cecum), 18.2 (ascending colon), 18.3 (hepatic flexure of colon), and 18.4 (transverse colon). LSCC included with codes 18.5 (splenic flexure of colon), 18.6 (descending colon), 18.7 (sigmoid colon), and 19.9 (rectosigmoid). Propensity score matching method using greedy matching with a ratio of 1:1 and caliper of 10-5 was used to adjust for sex, race, cancer stage (1-4), cancer grade, age at diagnosis, surgery and year of diagnosis. Primary tumor location (RSCC vs. LSCC) survival analyses were conducted using the Kaplan-Meier method as well as adjusted hazard ratios for 5-year all-cause mortality (OS), and 5-year cancer-specific mortality (CSS) were obtained using Cox proportional hazards regression.

RESULTS : Overall, 73,134 patients (33,947 [46.6 %] with right-sided, 39,187 [53.4 %] with left-sided colon cancer) were eligible. In multi-variable analysis, patients with LSCC had better overall (hazard ratio [HR] = 0.86, 95 % CI:0.86–0.88, P < 0.001) and cancer-specific survival (HR = 0.86, 95 % CI:0.84–0.88, P < 0.001) compared to patients with RSCC. After propensity score matching, the prognosis of LSCC was not statistically different from RSCC regarding overall (HR = 1.01, 95 % CI: 0.98 − 1.04, P <=0.6173).

CONCLUSIONS : Multivariate analysis showed that patients with RSCC had worse overall and cancer-specific survival compared to patients with LSCC. According to results from propensity score matching, the different outcome maybe be due to other confounding impacts, but not due to tumor location.