Terminal transferase expression in the differential diagnosis of acute leukemias. Eastern Cooperative Oncology Group

Acute leukemia immunohistochemistry: a systematic diagnostic approach

CONTEXT

The diagnosis and classification of leukemia is becoming increasingly complex. Current classification schemes incorporate morphologic features, immunophenotype, molecular genetics, and clinical data to specifically categorize leukemias into various subtypes. Although sophisticated methodologies are frequently used to detect characteristic features conferring diagnostic, prognostic, or therapeutic implications, a thorough microscopic examination remains essential to the pathologic evaluation. Detailed blast immunophenotyping can be performed with lineage- and maturation-specific markers. Although no one marker is pathognomonic for one malignancy, a well-chosen panel of antibodies can efficiently aid the diagnosis and classification of acute leukemias.

OBJECTIVE

To review important developments from recent and historical literature. General immunohistochemical staining patterns of the most commonly encountered lymphoid and myeloid leukemias are emphasized. The goal is to discuss the immunostaining of acute leukemias when flow cytometry and genetic studies are not available.

DATA SOURCES

A comprehensive review was performed of the relevant literature indexed in PubMed (National Library of Medicine) and referenced medical texts. Additional references were identified in the reviewed manuscripts.

CONCLUSIONS

Immunophenotyping of blasts using an immunohistochemical approach to lymphoid and myeloid malignancies is presented. Initial and subsequent additional antibody panels are suggested to confirm or exclude each possibility in the differential diagnosis and a general strategy for diagnostic evaluation is discussed. Although the use of immunohistochemistry alone is limited and evaluation by flow cytometry and genetic studies is highly recommended, unavoidable situations requiring analysis of formalin-fixed tissue specimens arise. When performed in an optimized laboratory and combined with a careful morphologic examination, the immunohistochemical approach represents a useful laboratory tool for classifying various leukemias.

Adult acute lymphoblastic leukemia

Much progress has been made in understanding the biology of and therapy for acute lymphoblastic leukemia (ALL). This progress has translated into the recognition of several subgroups of ALL and the institution of risk-adapted therapies. New therapies are emerging based on the definition of specific cytogenetic-molecular abnormalities. Changes in the pathologic classification of ALL have led to therapeutic consequences. Adaptation of successful treatment strategies in children with ALL has resulted in similar complete remission rates in adults. Prognosis has Improved especially in mature B-cell ALL and T-cell lineage ALL. However, regardless of ALL subgroup, long-term survival in adults is still inferior to that in children. Development of new drugs and agents tailored to subset-specific cytogenetic-molecular characteristics is vital to the therapeutic success in adult ALL.

Pathologic diagnosis of acute lymphocytic leukemia

With present knowledge, the optimal management of individual patients with acute leukemia requires that every case be studied by morphology, cytochemistry, cytogenetic, immunologic and molecular techniques. An algorithm for diagnostic evaluation and classification of ALL is provided in Fig. 11. Other techniques, such as DNA or cDNA [figure: see text] microarray, are at present important research tools but have not yet had a major effect on patient care. More detailed studies of individual patients need to be conducted at specialized cancer centers, where preservation of cells, DNA, RNA, or protein is possible. Such investigations will yield important information on the clinical importance of the expression of various markers, the prevalence and relevance of bilineage and biphenotypic leukemias, and above all will reveal the mechanisms of leukemogenesis and of disease evolution. Such insights will further aid clinicians in treating ALL and in preventing refractory disease.

Acute myeloid leukaemia expressing the leucocyte integrin CD11b-a new leukaemic syndrome with poor prognosis: result of an ECOG database analysis. Eastern Cooperative Oncology Group

While assessing the prognostic implications of immunophenotyping in 382 patients enrolled in treatment protocols of the Eastern Cooperative Oncology Group (ECOG) for de novo adult acute myeloid leukaemia, we identified 95 patients with a unique antigen profile characterized by high expression of the leucocyte integrin CD11b (CD11b+ AML). High expression of CD11b was defined as > or = 32% positive blasts based on the retrospectively established prognostic cut-off point for this antigen. Although CD11b is normally expressed by mature monocytes, natural killer cells and granulocytes, leukaemic blasts in CD11b+ AML lacked other immunologic monocytic features (e.g. CD14 and CD122, the interleukin-2 receptor beta chain) and demonstrated a high degree of immaturity, as reflected by a high incidence of blasts expressing the stem cell factor receptor, CD117, and few blasts positive for the myeloid differentiation antigen CD15. Furthermore, by FAB criteria, only 41% of CD11b+ AML cases were classified as M4/M5. Patients with CD11b+ AML had a low response rate (54%) when compared with acute monocytic leukaemia (AMOL; 82%, P = 0.006) or AML overall (68%, P = 0.031), independent of age, cytogenetic abnormalities and P-glycoprotein expression. Because of its poor prognosis, recognition of CD11b+ AML is clinically warranted and, given its morphologic and cytogenetic ambiguity, must be based on the unique antigen profile.