Acute lymphoblastic leukemia (ALL) results from malignant transformation of lymphoid progenitor cells in the bone marrow, producing clonal proliferation of immature lymphoblasts that crowd out normal hematopoietic cells, causing bone marrow failure. The leukemic blasts acquire multiple genetic mutations (including Philadelphia chromosome translocation t(9;22) in some adult cases) that confer growth advantages through dysregulated cell cycle progression, impaired apoptosis, and blocked differentiation. Bone marrow failure manifests as anemia (fatigue, pallor, dyspnea), neutropenia (recurrent infections, fever), and thrombocytopenia (petechiae, bruising, hemorrhage). Extramedullary infiltration can involve the CNS (headache, cranial nerve palsies, vomiting), liver, spleen, lymph nodes, and testes. The nurse monitors CBC with differential, implements neutropenic precautions (hand hygiene, dietary restrictions, avoiding live plants and raw foods), assesses for tumor lysis syndrome during induction chemotherapy (hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia, acute kidney injury), administers chemotherapy safely per protocol, manages central venous access, provides meticulous mouth care to prevent mucositis, and supports the patient through the prolonged treatment course (2-3 years for maintenance therapy).