summary Leukemia is a malignant neoplastic proliferation of lymphocytes and lymphocyte precursors. Patients typically present before the age of 4 with recurrent infections, bleeding, fatigue, and lymphadenopathy. Diagnosis is made with a bone marrow biopsy. Treatment is usually chemotherapy. Etiology Forms include acute lymphocytic leukemia (ALL) neoplastic proliferation of lymphocytes actue myeloblastic leukemia (AML) neoplastic proliferation of myeloblasts chronic myelocytic leukemia (CML) neoplastic mature myeloid cells (granulocytes) chronic lymphocytic leukemia (CLL) neoplastic proliferation of naive B cells Classification ALL represents 80% of cases of leukemia peak incidence of 4 years of age causes dimeralization of bones, periostitis, and lytic lesions positive TdT nuclear staining T-ALL proliferation of T-lymphocytes presents in teenagers B-ALL proliferation of B-lymphocytes 12;21 translocation most commonly seen in children 9;22 translocation most commonly seen in adults AML most commonly seen in older adults (5th-6th decade) marrow failure secondary to crowding out of normal hematopoiesis by neoplastic proliferation myeloblasts with Auer rods Acute Promyelocytic Leukemia (APL) caused by 15;17 translocation disrupts retinoic acid receptor (RAR) required for myeloblast maturation Acute megakaryoblastic leukemia associated with Down syndrome younger than 5 years Acute monocytic leukemia infiltration of the gums CML onset usually in older adults (5th-6th decade) 9;22 translocation known as the Philadelphia chromosome results in a fusion tyrosine kinase with increased activity (bcr-abl) increased levels of bcr-abl leads to ↑ cell division and inhibition of apoptosis CLL commonly seen in older adults (5th-6th decade) insidious onset of symptoms smudge cells on peripheral smear Presentation Symptoms recurrent infections bleeding fatigue lymphadenopathy (more common in CLL) Physical exam hepatosplenomegaly secondary to leukemic infiltrate lymphadenopathy secondary to leukemic infiltrate Treatment Nonoperative chemotherapy T-ALL & B-ALL may predispose to pathologic fractures all-trans-retinoic acidfor APL (AML subtype) imatinib for CML