*6.6.1 Morphology and immunophenotype*

The neoplasm is composed of infiltration of lymphocytes, plasma cells, and plasmacytoid lymphocytes in varying proportions, often accompanied by mast cell hyperplasia. The lymphoid cells expresses CD20 and surface Ig, the plasma cells secretes the same Ig that is expressed on the surface of the lymphoid cells. This is usually IgM but can also be IgG or IgA (**Figure 6**).
