Used primarily in chemotherapy to treat certain types of brain tumors, such as glioblastoma multiforme and medulloblastoma. It is also effective in treating multiple myeloma and lymphoma. Administered intravenously or as a wafer implanted directly into the brain after tumor removal, it works by inhibiting DNA and RNA synthesis, thereby preventing cancer cell growth. Additionally, it is sometimes used topically for certain skin lymphomas, such as mycosis fungoides, or in combination with other drugs to enhance its therapeutic effects. Due to its potent nature, careful monitoring is required to manage potential side effects, including bone marrow suppression and lung toxicity.