Histological variety of floral variant of follicular lymphoma

To further clarify the histopathological findings of the floral variant of follicular lymphoma (FVFL), we studied 13 Japanese cases. Two histological subtypes of neoplastic follicles of FVFL have been described: (i) A macrogerminal center pattern where the mantle zone lymphocytes were invaginated into the neoplastic germinal center, often reminiscent of a floral design. (ii) A microgerminal center pattern where the massive invasion of mantle zone lymphocytes resulted in almost complete breakage of the neoplastic follicles. In the former pattern, the neoplastic germinal center usually contained large clusters of tumor cells, whereas in the latter, small clusters of up to 20 tumor cells or isolated tumor cells were observed in the neoplastic germinal centers. Moreover, occasional tumor cells showed a lymphocytic and/or histiocytic Reed-Sternberg cell (L&H cells)-like morphology. Both types of neoplastic follicles were observed to a varying degree in most cases. The macrogerminal center pattern was predominant in nine cases (70%), whilst the microgerminal center pattern was predominant in only four cases (30%). Three lesions (23%) had a marginal zone component. Immunohistochemistry showed that atypical follicular center cells, including L&H cells, were CD3-, CD5-, CD10+, CD20+, CD43-, bcl-2+, cyclinD1-. The overall histological findings of the macrogerminal center are similar to those of florid progressive transformation of germinal center (PTGC), whilst the microgerminal center pattern is similar to that of nodular lymphocyte-predominant Hodgkin lymphoma. Initially, the differential diagnosis between FVFL and florid PTGC was emphasized. However, the present study indicates that nodal marginal zone B-cell lymphoma possessing floral follicles and nodular lymphocyte-predominant Hodgkin lymphoma should be added to the differential diagnosis of FVFL. The germinal center B-cell nature of FVFL is most clearly recognizable by immunohistochemistry, though histological appearance alone may cause some diagnostic problems.