A spindle cell variant of diffuse large B-cell lymphoma possesses genotypic and phenotypic markers characteristic of a germinal center B-cell origin

Lymphoma with prominent spindle cell features, the so-called spindle cell lymphoma, is an unusual morphological variant of diffuse large B-cell lymphoma. Five new cases of spindle cell lymphoma have been analyzed by a multiparameter approach in order to clarify its clinical and biological features. All patients presented advanced stage disease with extranodal involvement. Vagina was the most common extranodal site. All patients received chemotherapy and are alive in complete remission. Morphologically, all five cases exhibited proliferation of spindle cells with a vaguely storiform pattern highly suggestive of spindle cell neoplasms of nonlymphoid origin. In contrast, the results of immunohistochemical analysis indicated that all five cases were hematolymphoid neoplasms of the B-cell lineage. These lymphomas consisted of a B-cell clonal population which exhibited somatic immunoglobulin and BCL-6 mutations as well as BCL-6 protein expression. The neoplastic spindle cells therefore closely resemble B cells residing in the germinal center. The absence of MUM1 expression in neoplastic spindle cells suggested that neoplastic spindle cells may be related to the early phases of intragerminal center maturation of B cells. The germinal center phenotype, with restricted expression of BCL-6, was associated with the presence of a primary extranodal origin, normal lactate dehydrogenase levels, and good response to treatment.