Can cutaneous low-grade B-cell lymphoma transform into primary cutaneous diffuse large B-cell lymphoma? An immunohistochemical study of 82 cases.

Low-grade B-cell lymphomas of the skin, especially, primary cutaneous follicle center cell lymphoma has several distinctive features when compared with nodal/systemic follicular lymphomas, as they are frequently negative for bcl-2 and CD10, and only fewer than 25% of the cases show a bcl-2 rearrangement. The risk of transformation of a cutaneous low-grade B-cell lymphoma, such as primary cutaneous follicle center cell lymphoma, to primary cutaneous diffuse large B-cell lymphomas (PCDLBCL) has not been clearly delineated in the literature. Transformation of systemic/nodal follicular lymphoma into aggressive DLBCL is associated with rapid disease progression, refractoriness to treatment, and poor prognosis. The authors studied 82 cases of primary cutaneous DLBCL using antibodies for follicular dendritic cells (FDCs), CD21, and CD35 to detect networks of FDCs that could possibly indicate transformation of preexisting low-grade B-cell lymphoma to PCDLBCL. All cases were classified as PCDLBCL using strict histologic and immunophenotypic criteria. Fifty-three cases were classified as primary cutaneous DLBCL of "leg type," and 29 cases were classified as primary cutaneous DLBCL, "NOS" category. Immunohistochemical studies were performed in all 82 cases; in 15 cases, a CD21/CD35+ network of FDCs was noted within the tumor, indicating the presence of remnants of residual germinal centers, suggesting the possibility of a transformed low-grade B-cell lymphoma. In summary, the authors' findings seem to indicate that some cases of primary cutaneous DLBCL may result from transformation of a low-grade B-cell lymphoma. Further studies are necessary to evaluate the significance of their findings by using ancillary techniques including genetic analysis.