Lymph node histology in typical and atypical chronic lymphocytic leukemia

According to the French-American-British (FAB) proposal on the classification of chronic lymphoid leukemia (CLL), the disorder can be subdivided into typical and atypical CLL. We recently demonstrated the prognostic significance of this subgrouping and based on these results we suggested that typical and atypical CLL represent two closely related, but different entities. These results prompted us to investigate 42 patients diagnosed with CLL based on the results of lymph node biopsy in order to identify the histologic counterpart of the CLL variants. A first group of 14 cases showed a monomorphic proliferation of small round lymphocytes associated with the occurrence of small pseudofollicles. All these cases were diagnosed as typical CLL on peripheral blood (13 cases) or bone marrow smear (1 case). The remaining 28 cases showed aberrant histologic features characterized by the presence of large numbers of paraimmunoblasts and prolymphocytes, forming very large pseudofollicles, and/or by nuclear irregularities of the neoplastic cells. Based on peripheral blood smears (22 cases) or bone marrow smears (six cases), two cases showed no peripheral blood involvement, 21 cases were diagnosed as atypical CLL, and five as typical CLL. From these data we can conclude that a histologic counterpart of the CLL variants recognized in the FAB proposal does exist; moreover, our data may explain reports on lymph node involvement by CLL composed of small cleaved cells and clarify the occurrence of pseudofollicles in cases described as mantle cell lymphomas.