Stage-based Variation in the Effect of Primary Tumor Side on All Stages of Colorectal Cancer Recurrence and Survival.

Background: Multiple studies have defined the prognostic and potential predictive significance of the primary tumor side in metastatic colorectal cancer (CRC). However, the currently available data for early-stage disease are limited and inconsistent.
Materials and Methods: We explored the clinicopathologic, treatment, and outcome data from a multisite Australian CRC registry from 2003 to 2016. Tumors at and distal to the splenic flexure were considered a left primary (LP).
Results: For the 6547 patients identified, the median age at diagnosis was 69 years, 55% were men, and most (63%) had a LP. Comparing the outcomes for right primary (RP) versus LP, time-to-recurrence was similar for stage I and III disease, but longer for those with a stage II RP (hazard ratio [HR], 0.68; 95% confidence interval [CI], 0.52-0.90; P < .01). Adjuvant chemotherapy provided a consistent benefit in stage III disease, regardless of the tumor side. Overall survival (OS) was similar for those with stage I and II disease between LP and RP patients; however, those with stage III RP disease had poorer OS (HR, 1.30; 95% CI, 1.04-1.62; P < .05) and cancer-specific survival (HR, 1.55; 95% CI, 1.19-2.03; P < .01). Patients with stage IV RP, whether de novo metastatic (HR, 1.15; 95% CI, 0.95-1.39) or relapsed post-early-stage disease (HR, 1.35; 95% CI, 1.11-1.65; P < .01), had poorer OS.
Conclusion: In early-stage CRC, the association of tumor side and effect on the time-to-recurrence and OS varies by stage. In stage III patients with an RP, poorer OS and cancer-specific survival outcomes are, in part, driven by inferior survival after recurrence, and tumor side did not influence adjuvant chemotherapy benefit.
(Crown Copyright © 2018. Published by Elsevier Inc. All rights reserved.)