LAUSR

ABSTRACT Introduction Colorectal cancer is a heterogenous disease, with various clinical and molecular subtypes related to the primary site (left versus right colon) of the original tumor. Primary colon tumor side is both a prognostic and predictive marker in metastatic colorectal cancer. Areas covered There is an increasing body of evidence for how primary site may impact treatment decisions in metastatic colorectal cancer. We reviewed the evidence for its prognostic and predictive value. Expert opinion Primary site is a prognostic marker in metastatic colorectal cancer, with right colon tumors being associated with more aggressive disease behavior and poorer outcomes. Primary site also appears to predict for outcomes to various treatments, in particular anti-EGFR antibodies. As our understanding and testing of the molecular and biological differences within colorectal cancer increases beyond primary site, this should be integrated into the current treatment algorithm to ensure an individualized patient-centered approach to care.