Used primarily in the treatment of non-small cell lung cancer and malignant pleural mesothelioma, this compound functions as an antifolate agent that inhibits multiple enzymes involved in folate metabolism, including thymidylate synthase, dihydrofolate reductase, and glycinamide ribonucleotide formyltransferase. By disrupting DNA and RNA synthesis, it impedes the growth of rapidly dividing cancer cells. It is typically administered in combination with platinum-based chemotherapy agents such as cisplatin. Due to its mechanism of action, patients are often pre-treated with folic acid and vitamin B12 to reduce toxicity and improve tolerability. Its use is limited to specific cancer types and requires careful patient selection and monitoring.