Alemtuzumab, a humanized monoclonal antibody, is thought to destroy cancer cells through immune system stimulation or apoptosis induction (programmed cell death). In case series studies using alemtuzumab as salvage therapy, about a third of patients with B-cell chronic lymphocytic leukemia (B-CLL), who were otherwise refractory to chemotherapy, improved. Anti-tumour activity was also observed when the drug was used as first-line therapy or to treat minimal residual disease. Adverse events associated with alemtuzumab included "first-dose" flu-like symptoms, prolonged lymphopenia with a subsequent increased risk of opportunistic infections and viral reactivation (e.g., cytomegalovirus) and transient cytopenias. Data from randomized controlled trials (RCTs), focusing on clinical outcomes such as survival and patients' quality of life, are needed to accurately assess the harm and benefit of alemtuzumab.