Prognostic and predictive impact of primary tumor sidedness for previously untreated advanced colorectal cancer

Pooled analysis of 12 first-line randomized trials (9,277 patients) of first-line anti-EGFR plus chemotherapy versus chemotherapy alone for mCRC found that patients with left-sided primary tumor had better OS and PFS than patients with right-sided primary tumor. This prognostic value of primary tumor sidedness (PTS) was restricted to the KRAS-wildtype population. PTS was predictive of cetuximab efficacy, with a statistically significant improvement of survival for patients with left-sidedness. These results suggest that treatment choice in mCRC should be based on both PTS and KRAS-status.