Definition:

Lymphoplasmacytic lymphoma (LPL)/Waldenstrom's macroglobulinemia (WM) is a non-Hodgkin lymphoma (NHL) subtype. LPL/WM is a neoplasm of small B-lymphocytes, plasmacytoid lymphocytes, and plasma cells, usually involving bone marrow, lymph nodes, and the spleen. WM can be distinguished clinically from LPL on the basis of a detectable IgM monoclonal spike in serum. In the general population, LPL/WM is a very rare disease, accounting for only 1%-2% of all hematologic malignancies, reflected in an incidence rate of 3-4 cases per million people per year. The t(9;14)(p13;q32) is present in near 50% of cases of LPL. This chromosomal translocation involves a junction between 9p13 and the switch micro region of the Ig heavy chain locus on 14q32. The 9p13 breakpoint contains the PAX-5 gene which encodes a B-cell specific transcription factor involved in the control of B-cell proliferation and differentiation. The translocation causes the juxtaposition of the PAX-5 gene to the IgH locus in the opposite direction of transcription, resulting in an 11-fold over-expression of PAX-5 mRNA.