Primary testicular diffuse large B-cell lymphoma belongs to the nongerminal center B-cell-like subgroup: A study of 18 cases.

The most common type of primary testicular lymphoma is diffuse large B-cell type, which has the potential for aggressive clinical behavior. Diffuse large B-cell lymphoma can be further subclassified into two major prognostic categories: germinal center B-cell-like and nongerminal center B-cell-like. Such distinction is made possible using the immunohistochemical expression of CD10, Bcl-6 and MUM1. The aim of this study was to stratify primary testicular lymphoma of the diffuse large B-cell type according to this scheme. Immunohistochemical stains for CD10, Bcl-6 and MUM1 were performed on 18 cases of primary testicular lymphoma of diffuse large B-cell type. Subclassification was carried out as previously described where CD10 and/or Bcl-6 positivity and negativity for MUM1 were considered indicative of germinal center B-cell-like type and the opposite expression as nongerminal center B-cell-like type. The proliferative activity was determined using immunostaining with the Ki-67 antibody. Of 18 cases, 16 (89%) were found to belong to the nongerminal center B-cell-like type. Two cases (11%) were classified as germinal center B-cell-like type; one had a CD10-positive, Bcl-6-positive and MUM1-negative profile, and the other was CD10 negative, Bcl-6 positive and MUM1 negative. The former occurred in a 38-year-old patient who was human immunodeficiency virus positive. All the cases expressed high proliferative activity (> or =50% Ki-67 labeling). We conclude that most (89%) primary testicular lymphomas of the diffuse large B-cell type belong to the nongerminal center B-cell-like subgroup and have high proliferative activity.