Prognostic and Predictive Relevance of Primary Tumor Location in Patients With RAS Wild-Type Metastatic Colorectal Cancer

Metastatic colorectal cancer (mCRC) is heterogeneous, and primary tumors arising from different regions of the colon are clinically and molecularly distinct.

To examine the prognostic and predictive value of primary tumor location in patients with RAS wild-type (wt) mCRC treated with first-line fluorouracil, leucovorin, and irinotecan (FOLFIRI) plus cetuximab in the Cetuximab Combined With Irinotecan in First-line Therapy for Metastatic Colorectal Cancer (CRYSTAL) trial and FOLFIRI Plus Cetuximab Versus FOLFIRI Plus Bevacizumab as First-Line Treatment For Patients With Metastatic Colorectal Cancer (FIRE-3) trial. DESIGN, SETTING, AND PARTICIPANTS: In this retrospective analysis patients with RAS wt metastatic colorectal cancer from the CRYSTAL and FIRE-3 trials were classified as having left-sided or right-sided mCRC, defined, respectively, as patients whose tumors originated in the splenic flexure, descending colon, sigmoid colon, or rectum vs appendix, cecum, ascending colon, hepatic flexure, or transverse colon. MAIN OUTCOMES AND MEASURES: Progression-free survival (PFS), overall survival (OS), and objective response rate (ORR) were assessed according to tumor location and treatment arm.