Prognosis in stage II colorectal cancer: the effect of the primary tumour location and biomarkers — a retrospective cohort study

Background The prognostic impact of primary tumour location (right- vs left-sided) is well-established in stage III/IV colorectal cancer (CRC), with right-sided tumours associated with poorer outcomes. However, its prognostic role in stage II CRC remains unclear. This study investigates whether the worse outcomes observed in advanced right-sided cancers also apply to early-stage CRC, or if they may be influenced by other factors such as patient demographics and molecular biomarkers. Clarifying this could help improve risk stratification in clinical practice. Methodology For this study, we analysed data of all Belgian patients diagnosed with stage II CRC in 2015-2016 (n = 3.278, data obtained from the Belgian Cancer Registry). Information on primary tumour location, demographics, pathologic T-category, molecular biomarkers (including MSI, BRAF and KRAS status) and overall survival (OS) was collected. Results In the univariable analysis, patients with stage II right-sided colon cancer had a significantly worse OS than left-sided colon cancer. Furthermore, advanced age and pT4 were also associated with worse OS. However, in the multivariable analysis, only gender, age, and pathologic T-category significantly affected OS. Primary tumour location was not significantly associated with OS in the multivariable analysis. Furthermore, the molecular biomarkers did not show a significant effect in either analysis. However, due to the limited size of the multivariable cohort, these results should be interpreted with caution. Conclusion The primary tumour location is not an independent prognostic factor in stage II CRC with a confounding effect of age. Notably, molecular biomarkers did not affect the prognosis in either uni- or multivariable analysis.