5-Fluorouracil is widely used in the treatment of various types of cancer, including colorectal, breast, stomach, and pancreatic cancers. It works by inhibiting the synthesis of DNA and RNA, which prevents cancer cells from growing and dividing. In dermatology, it is applied topically to treat actinic keratosis and certain types of skin cancer, such as superficial basal cell carcinoma. Additionally, it is used in combination with other chemotherapeutic agents to enhance its effectiveness in combating more aggressive forms of cancer. Its ability to target rapidly dividing cells makes it a valuable tool in both systemic and localized cancer therapies.