ICD-11

An indolent, mature B-cell neoplasm composed of small, round B-lymphocytes. When the bone marrow and peripheral blood are involved, the term chronic lymphocytic leukaemia is used. The term small lymphocytic lymphoma is restricted to cases which do not show leukemic involvement of the bone marrow and peripheral blood.

Chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL) is a neoplasm composed of monomorphic small, round to slightly irregular B lymphocytes in the peripheral blood (PB), bone marrow (BM), spleen and lymph nodes, admixed with prolymphocytes and paraimmunoblasts forming proliferation centres in tissue infiltrates. The CLL/SLL cells usually coexpress CD5 and CD23. In the absence of extramedullary tissue involvement, there must be <5x109/L monoclonal lymphocytes with a CLL phenotype in the PB. The International Workshop on Chronic Lymphocytic Leukemia (IWCLL) report requires that the lymphocytosis be present for at least 3 months and also allows for the diagnosis of CLL to be made with lower lymphocyte counts in patients with cytopenias or disease-related symptoms. Whether patients who would have fulfilled the criteria in the past for CLL but who fulfill the criteria only for monoclonal B lymphocytosis (MBL) are better considered to have low stage CLL or MBL remains to be determined. Some may prefer to still consider many of these cases more like CLL. The term SLL is used for non-leukaemic cases with the tissue morphology and immunophenotype of CLL. The IWCLL definition of SLL requires lymphadenopathy, no cytopenias due to BM infiltration by CLL/SLL and <5x109/L PB B-cells.