Used primarily as an anticancer agent, especially in the treatment of solid tumors such as colorectal, breast, and skin cancers. It functions by inhibiting thymidylate synthase, disrupting DNA synthesis and cell division in rapidly growing cancer cells. Also applied topically for precancerous skin conditions like actinic keratosis and certain types of basal cell carcinoma. Its ability to interfere with RNA and DNA metabolism makes it effective in both systemic and localized cancer therapies.