Chromosomal abnormalities play a central role in the pathogenesis, diagnosis, and monitoring of treatment of many hematologic disorders. The observation of a chromosomally abnormal clone is consistent with a clonal neoplastic process. Certain chromosome abnormalities can help classify the type of lymphoma. For example, t(14;18)(q32;q21.3) involving the IGH and BCL2 genes is usually indicative of a follicular lymphoma. A translocation between MYC and IGH genes or a t(8;14)(q24.1;q32) are both associated with Burkitt lymphoma. Cytogenetic studies often can help distinguish between B-cell and T-cell disorders. Structural abnormalities involving breakpoints at any immunoglobulin locus is consistent with a B-cell disorder; structural abnormalities involving breakpoints at a T-cell receptor site are usually associated with a T-cell disorder.