Fluoropyrimidines have long represented the cornerstone of treatment for colorectal cancer.1 Such compounds act primarily as inhibitors of thymidylate synthase, the rate-limiting enzyme in the synthesis of pyrimidine
nucleotides.2 Fluorouracil has been combined with folinic acid (also known as leucovorin) to enhance the capacity of fluorouracil to bind to thymidylate synthase.2 The addition of irinotecan (FOLFIRI) or oxaliplatin (FOLFOX) to fluorouracil and folinic acid, in combination with either a vascular endothelial growth factor inhibitor (bevacizumab) or an epidermal growth factor inhibitor (e.g., cetuximab or panitumumab) if the tumor contains a wild-type RAS gene, represents contemporary standard therapy and has extended the median survival among patients with metastatic colorectal cancer to almost 30 months