Primary cutaneous B-cell lymphoma and lymphoproliferative disorders of skin: current status of pathology and classification.

Cutaneous B-cell lymphomas (CBCLs) are rare and are usually secondary to systemic nodal lymphoma. These lymphomas account for about 20% of all cutaneous lymphomas. Only recently has the existence of B-cell lymphoma presenting clinically in the skin without evidence of extracutaneous involvement been accepted as primary CBCL. The application of immunohistochemistry and molecular analysis has shown that some cases of cutaneous lymphoid hyperplasia and pseudolymphomas contain a monoclonal population of B cells and are therefore considered true lymphomas. The pathology and classification of this heterogeneous group of lymphoproliferative disorders is reviewed. The main entities comprise marginal zone lymphoma, lymphoplasmacytoid lymphoma (immunocytoma), follicular center cell lymphoma, mantle cell lymphoma, large cell lymphoma (immunoblastic and anaplastic), intravascular lymphomatosis, plasmacytoma, and lymphoblastic lymphoma.