5-Fluorouracil is an antimetabolic chemotherapeutic agent whose mechanism of action against cancer is its activation into fluorouracil deoxyribonucleotide upon entry into the body, which inhibits thymidylate synthase, thereby inhibiting cellular DNA synthesis. 5-Fluorouracil also has a slight inhibitory effect on cellular RNA synthesis, which ultimately affects cell proliferation. 5-fluorouracil also has a slight inhibitory effect on RNA synthesis, which ultimately affects cell proliferation, most notably in the DNA synthesis phase of the cell, and also in other phases of the cell cycle. Through these mechanisms of action, 5-fluorouracil can play its role in anti-cancer therapy, and is mainly used clinically for the treatment of advanced colorectal cancer, breast cancer, ovarian cancer and other malignant tumors.