B-cell cutaneous lymphoid hyperplasia representing progressive transformation of germinal center: a report of 2 cases.

Cutaneous lymphoid hyperplasia (CLH) is a reactive polyclonal benign lymphoproliferative process predominantly composed of B cells or T cells, either localized or disseminated. The authors report histomorphologic, immunophenotypic, and genotypic findings of 2 cases of B-cell CLH demonstrating progressive transformation of germinal center (PTGC). Histologically, most of the lymphoid follicles were PTGCs with a few hyperplastic germinal centers. PTGC was characterized by enlarged but well-circumscribed follicles without clear demarcation of the germinal center and mantle zone, which contained a predominance of small lymphocytes and variable numbers of centrocytes, centroblasts, and immunoblasts. However, there were no centroblasts and immunoblasts resembling lymphocytic and/or histiocytic Reed-Sternberg cell variants in nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) in either lesion. These unusual CLHs should be differentiated from the primary cutaneous marginal zone B-cell lymphoma, primary cutaneous follicular lymphoma, particularly "floral variant," or NLPHL. To avoid overdiagnosis and overtreatment, immunophenotypic and genotypic studies are required along with careful morphologic examination.