Neoplastic B-cell proliferations (chronic leukemias and lymphomas) are clonal expansions of cells that express either kappa or lambda immunoglobulin light chains.

Chronic lymphocytic leukemia (CLL) is a clonal lymphoproliferative disorder usually of B-cell origin (95%), that has been traditionally diagnosed using clinical and morphologic criteria. Incorporation of immunophenotypic features into the diagnostic criteria is helpful in separating common B-cell CLL from other lymphoproliferative disorders. Detection of karyotypic abnormalities is useful in assessing prognosis. Lymphocytes in B-CLL coexpress CD19, CD20, and CD23 pan B-cell antigens, CD5, pan T-cell antigen, and a single immunoglobulin light chain, kappa or lambda. CD10 (CALLA) expression is usually absent. Mantle cell lymphoma is distinguished from CLL by absent or very dim expression of CD23.

Lymphomas are biologically complex neoplasms of the immune system. Numerous classification schemes have been developed based on morphologic features. This limited approach is often unreliable. Immunophenotyping, by flow cytometry and/or immunohistochemistry, has emerged as a valuable adjunct to conventional morphologic diagnosis and classification. Flow cytometry offers the advantage of rapid multiparameter analysis. Combining light scatter characteristics with patterns of antigen expression and DNA content provides biological information that is useful in making a diagnosis and assessing prognosis. Various gating strategies can be employed to enhance the detection of minor populations, thus providing a level of sensitivity comparable to molecular methods (gene rearrangement studies).

T-cell CLL, unlike B-CLL, is associated with rapid onset, an aggressive clinical course poorly responsive to therapy and decreased survival. Immunophenotyping, in the majority of cases, demonstrates texpression of CD3 (a pan T-cell antigen), and CD4 (the helper cell antigen). CD8 (the suppressor/cytotoxic cell antigen) is usually not expressed. Genotyping demonstrates a clonal rearrangement of the T-cell receptor gene.

Large granular lymphocyte (LGL) proliferations can be divided into T-cell and natural killer (NK) cell subsets by immunophenotyping. The more common T-cell type expresses CD3, a pan T-cell antigen and CD8, the suppressor/cytotoxic cell antigen. Genotyping demonstrates a rearrangement of the T-cell receptor gene. The NK cell type is relatively rare and expresses CD2 and CD16 and/or CD56. CD3 expression is absent. Genotyping demonstrates a germline configuration of the T-cell receptor gene.

In S'ezary syndrome, the neoplastic lymphocytes aer T cells with a helper cell phenotype. Expression of CD7, a pan T-cell antigen, is absent and is useful in distinguishing the neoplastic cells from normal T-helper cells. Genotyping demonstrates a clonal rearrangement of the T-cell receptor gene.

In adult T-cell leukemia/lymphoma, the neoplastic lymphocytes are T-cells with a helper cell phenotype. Expression of CD3, CD4, and CD25 is present. Expression of CD7 is absent. Genotyping demonstrates a clonal rearrangement of the T-cell receptor gene.

Detection of a B-cell population coexpressing CD22, CD11c, adn CD25 is useful in establishing a diagnosis of hairy cell leukemia when used in conjunction with morphology and cytochemistry. Immunophenotyping by flow cytometry is a sensitive method for detecting residual or recurrent disease in the peripheral blood of patients with an established diagnosis.

Detection of a population of cells expressing CD38 and CD138 in the peripheral blood is useful in establishing a diagnosis of plasma cell leukemia when used in conjunction with morphology.

Lineage assignment in acute leukemia is necessary for selecting appropriate therapy and is useful in assessing prognosis. Multiparameter analysis using four-color immunophenotyping techniques is a rapid and specific method of assigning lineage in acute leukemia.

This profile is also useful in distinguishing lymphoid from myeloid blast crisis in CML and immunophenotyping lymphoblastic lymphoma in blood or bone marrow. Immunophenotyping and cytogenetic analysis are increasingly being used to supplement the traditional methods (morphology and cytochemistry) of classifying acute leukemias and to provide prognostic information. Acute lymphoblastic leukemia (ALL) can be classified into undifferentiated null T-and B-cell lineages. In all of B-cell lineage, expression of CD10 (CALLA) is a favorable prognostic factor. Acute myelogenous leukemias (AML) are a heterogeneous group. In cases where morphology and cytochemical staining is equivocal, immunophenotyping can be useful. Immunophenotyping is particularly useful in classifying megakaryoblastic leukemia (FABM7). A combination of characteristic light scattering properties and myeloid phenotype can suggest a diagnosis of acute promyelocytic leukemia (FABM3). Confirmation of the retinoic acid receptor gene rearrangement by cytogenetic or molecular methods is recommended. See PML-RARA Transcript Detection for Acute Promyelocytic Leukemia, Qualitative [480491], Chromosome Analysis, Leukemia/Lymphoma [052001], and related Fluorescence in situ Hybridization (FISH), Oncology [510362].