Colorectal cancer is the second leading cause of cancer death in the United States. At least 50% of patients develop metastases, and most of these patients have unresectable tumors. Treatment options for metastatic colorectal cancer (mCRC) include several lines of chemotherapy, salvage surgery, maintenance therapy, and local therapy. For decades, 5-fluorouracil (5-FU) was the only chemotherapy option for patients with mCRC. This changed markedly over the last decade with the approval of irinotecan, oxaliplatin, capecitabine, humanized monoclonal antibodies that target either vascular endothelial growth factor (bevacizumab, aflibercept, and ramucirumab) or the epidermal growth factor receptor (cetuximab and panitumumab), and, most recently, regorafenib and trifluridine/tipiracil. In this review, we focus on first-line treatments for mCRC. We discuss how results from multiple clinical trials over the last 10 to 20 years confirmed the benefit of adding oxaliplatin and irinotecan to the established 5-FU chemotherapy backbone, and then further defined benefit in certain patient subgroups with the addition of mAbs. Ongoing investigations attempt to illustrate the role of newer molecular and immune therapies in the fight against mCRC. We acknowledge the tremendous advances made in first-line mCRC treatment, admit that we still have a long way to go, and highlight exciting lines of research for patients with mCRC in the burgeoning fields of precision medicine and immunotherapy.
