FOLLICULAR LYMPHOMA OF COMPARTMENTALIZED SMALL CLEAVED CENTER CELLS AND MANTLE ZONE LYMPHOCYTES - EVIDENCE FOR A COMMON DERIVATION

The authors have observed a unique case of follicular lymphoma in which the central zones of neoplastic nodules were composed predominantly of small cleaved cells (SCC) that were surrounded by small lymphoid cells proliferating in wide mantles as in mantle zone (MZ) lymphoma. The central SCC component displayed a follicular SCC lymphoma-like phenotype (IgD-, CD10+, CD5-, CD68-), whereas the neoplastic cells of the peripheral zones had an MZ lymphoma-like phenotypic profile (IgD+, CD10-, CD5+, CD68+). In extranodal involved tissues, either follicular or diffuse (leukemic-like) patterns of lymphoma infiltration were noted. Flow cytometric analyses showed in the bone marrow or the peripheral blood two leukemic B cell populations, one mimicking the phenotypic profile (IgM+, IgD+, CD5+, CD10-, Leu8-) of small lymphoid cells with MZ-like features, and the other with phenotypic features (IgM+, IgD+, CD5+, CD10+, Leu8+) intermediate between those of MZ-like cells and those of the SCC component (follicular center-like) detected in the lymph node. Immunomagnetic sorting and gene rearrangement studies indicated that both CD10+ and CD10- B lymphocytes and lymph node neoplastic B cells shared the same clonal origin. This unusual follicular lymphoma can be viewed as the result of the proliferation of a single follicular progenitor capable of differentiating toward both a germinal center and an MZ phenotype. The simultaneous presence in the same patient of at least three neoplastic B-cell populations at different maturation stages, encompassing follicular center and MZ phenotypes, and showing the same clonal derivation, indicates a close lineage relationship between follicular SCC and MZ lymphomas.