Influence of first line chemotherapy strategy depending on primary tumor location in metastatic colorectal cancer

{Background: Primary tumor location (PTL) is a major prognostic factor in metastatic colorectal cancer (mCRC) with left side which present better prognosis than right sided. Uncertainty exists regarding comparative effectiveness of irinotecan or oxaliplatin doublet in mCRC in function of PTL. Methods: We conducted a retrospective comparing clinical outcomes from both regimens in function of sidedness. Patients with newly diagnosed mCRC candidates to first-line chemotherapy were selected. Clinical outcomes were assessed and stratified by tumor location (left, right and rectal) and type of treatment. Results: Overall, 702 patients met the inclusion criteria. Primary colon cancer was right-sided in 248 (35.3%) patients, left-sided in 296 (42.2%) and rectal in 158 (22.5%) patients. Whatever PTL monochemotherapy give poor progression-free survival (PFS) and overall survival (OS). Triplet give better PFS and OS only for rectal cancer. When looking at doublet in first line. Folinic acid, 5FU, and irinotecan (FOLFIRI) give better PFS in rectal cancer [PFS of 21.2 (95% CI: 14.9-NR) versus 12.2 (95% CI: 10.1- 13.4) months for the folinic acid, 5FU, and oxaliplatin (FOLFOX) group