Cytogenetics, fluorescence in situ hybridization (FISH) and molecular tests, especially polymerase chain reaction (PCR), play an important role in the management of patients with hematologic malignancies by helping to establish the diagnosis, as well as predict prognosis, response to treatment and disease progression. Chromosomal and molecular abnormalities provide the most reliable criteria for classification of hematopoietic tumors and often comprise the basis for targeted therapy.