Used primarily in the treatment of chronic lymphocytic leukemia (CLL), fludarabine is effective in inducing remission in both previously untreated and relapsed patients. It is often used as a single agent or in combination with other chemotherapeutics such as cyclophosphamide and rituximab (FCR regimen), which has shown improved response rates and progression-free survival. Fludarabine is also utilized in conditioning regimens prior to stem cell or bone marrow transplantation due to its immunosuppressive properties, helping to prevent graft rejection. Its ability to cross the blood-brain barrier makes it occasionally useful in treating lymphoid malignancies involving the central nervous system. However, prolonged use may increase the risk of autoimmune complications and severe immunosuppression, requiring careful patient monitoring.