Histopathological and molecular features of persistent polyclonal B-cell lymphocytosis (PPBL) with progressive splenomegaly.

Five cases of persistent polyclonal B-cell lymphocytosis (PPBL) with progressive splenomegaly are reported; three were splenectomized. BCL2/IGH rearrangements were found in three cases; HLA-DRB1*07 in all. Bone marrow (BM) trephines showed a moderate lymphoid infiltrate with intrasinusoidal distribution resembling a splenic marginal-zone lymphoma. Splenic white pulp revealed an enlargement of the marginal-zone area; red pulp was infiltrated by the same lymphocytes engulfing the sinuses. Splenic and BM B-lymphocytes were CD79a(+)/CD20(+)/IgM(+)/IgD(+)/bcl-2(+)/CD27(+)/DBA.44(-)/CD31(-) and polyclonal by immunophenotype/polymerase chain reaction. PPBL features an expansion of splenic marginal-zone B-lymphocytes, which infiltrate BM sinusoids and circulate in the blood with no evidence of clonality, even in cases with progressive splenomegaly.