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We evaluated the contributions of enzyme cytochemical stains and flow cytometric immunophenotyping (FCI) data to detection of monocytic cells (MCs) in acute myelomonocytic and acute monocytic leukemias (AMMLs and AMoLs) and compared FCI findings in AMoL, chronic myelomonocytic leukemia (CMML), and normal peripheral blood (PB) and bone marrow (BM) monocytes to classify and evaluate absolute monocytoses (AMs). We reviewed 10 AMMLs and 6 AMoLs with a-naphthyl-acetate esterase (ANAE) and a-naphthyl-butyrate esterase stains and a complete FCI profile and compared FCI data for 6 AMoLs, 7 CMMLs, 2 AMs, and normal monocytes. We confirmed increased sensitivity of ANAE staining to FCI data in detecting MCs in AMML and AMoL. CD14 was insensitive for confirming MCs; other characteristic markers of MCs were absent or partially lost in AMML and AMoL. Aberrant expression of CD56 (detected in 50% of AMMLs and AMoLs), CD34, and CD117 indicated malignancy. The mature MCs of the CMMLs revealed variable FCI abnormalities (partial loss of CD13, CD14, and CD15; expression of CD56), as in the monoblasts of AMoL. These FCI abnormalities in morphologically mature MCs might indicate markers for CMML. AMs revealed FCI abnormalities, indicating clues to their correct classification as CMML.

We have performed the cytochemical analysis (myeloperoxidase, ASD-chloroacetate and acid alpha-naphthylacetate esterases, Sudan black B) of blast cells from 25 acute leukemia patients, after 3, 5 and 7 days of liquid culture with conditioned medium from phytohemagglutinin stimulated leukocytes (PHA-LCM). In case of acute myeloid leukemia blast cells an increase of percentage of positive cells simultaneously with the enhancement of the cytochemical reactions was observed. This method may be useful for the precise diagnosis of poorly differentiated blasts with weak expression of cytochemical phenotype.

Immunohistochemical investigations were performed on decalcified, paraffin-embedded iliac crest trephine biopsy specimens from 30 cases of acute myeloid leukemia (AML, as defined by the FAB classification) with antibodies against B cells (L26, 4KB5, MB1, Ki-B3), T cells (UCHL1, MT1), myeloid/histiocytic cells (anti-neutrophil elastase, MAC387, anti-S-100 protein, anti-alpha 1-antichymotrypsin, DAKO-M1), natural killer/killer cells (anti-Leu-7), and megakaryocytes (anti-factor VIII-related antigen). (1) The blast cells of all the cases reacted with from at least two to at most eight different antibodies. Each antibody reacted with blast cells in a minimum of two (maximum 30) cases. (2) MT1, Ki-B3, anti-alpha 1-antichymotrypsin anti-neutrophil elastase, anti-S-100 protein, and MAC387 stained blast cells in more than 50% of the cases; MB1, L26, UCHL1, 4KB5, and DAKO-M1 in 20% to 50% of the cases; and anti-Leu-7 and anti-factor VIII-related antigen in less than 20% of the cases. (3) In the majority of cases many T lymphocytes, a small-to-moderate number of B lymphocytes, and a few Leu-7-positive lymphoid cells were intermingled with the blast cells. In some cases, especially where only a minor proportion of the blast cells was immunostained, it was nearly impossible to distinguish the lymphocytes of the tumor's stromal reaction from small blast cells. Thus, AML exhibits a heterogeneous immunophenotype in trephine biopsy specimens. Immunohistologic diagnosis of this disease in such specimens may be extremely difficult. Since staining of the blast cells with one or more of the antibodies generally used to define B cells, T cells, or their neoplastic derivatives is not uncommon, misinterpretation as non-Hodgkin's lymphoma of high-grade malignancy could easily occur. These findings also suggest that mixed-type (hybrid) acute leukemias with coexpression of myeloid and lymphoid cell markers could be more common than generally realized.

39 patients suffering from different subtypes of monocytic (M 5) and myelomonocytic (M 4) leukemia were analyzed retrospectively. In 8 cases a 'transitional myelomonocytic variant' was diagnosed; the leukemic cell in these patients is marked by morphological and cytochemical signs of monocytic and granulocytic precursors. As the correct diagnosis of this special subtype may be difficult, its place within the French-American-British (FAB) classification will be discussed.

Alpha-naphthyl acetate esterases (ANAE) were examined by cytochemical and isoelectric focusing (IEF) techniques in 48 cases of acute myeloid leukemia that were classified by conventional morphological criteria. Four main types of ANAE isoenzyme patterns were found by IEF, and comparisons with the expression of membrane receptors (Fc-IgG and C3b) and monocyte-specific antigens (UCHM1, UCHALF, and E11) suggest relationships between ANAE isoenzyme synthesis and distinct myeloid maturational stages. The results further indicate that the blast cells of acute myelomonocytic leukemia (AMML) may represent an immature variant of monocytic leukemia (AMoL) and that morphological examination alone is inadequate in the assessment of monocytic differentiation in acute myeloid leukemias. Inhibition studies of cytochemical ANAE activity with sodium fluoride (NaF) show that the presence of NaF-sensitive or NaF-resistant ANAE enzymes is often unrelated to the diagnostic category of acute leukemia. The results of this study are examined in relation to current concepts of myeloid differentiation, and the application of these findings to the subclassification of acute myeloid leukemias is discussed.

Membrane receptors for IgG and C3b were examined on blast cells from 57 cases of acute myeloid leukaemia. These acute leukaemias were classified as myeloblastic, myelomonocytic or monocytic following morphological, cytochemical, and immunological investigations. The membrane receptors of leukaemic blast cells appear to be directly related to the degree of monocytic differentiation with the lowest receptor activities found in acute myeloblastic leukaemia. A comparison was also made between receptor and cytoplasmic acid naphthyl acetate esterase (ANAE) activities in 29 morphologically and immunologically-defined myelomonocytic and monocytic leukaemias. This study revealed that the receptor-positive "monocytic component" in a significant proportion of cases showed unexpectedly weak or negative ANAE reactions suggesting a more cautious approach to the interpretation of ANAE cytochemistry in acute leukaemias. The normal development of cytoplasmic ANAE and membrane receptors is also discussed and compared with their abnormal patterns of expression associated with leukaemic transformation.

The relationship between cell features by light microscopy and therapeutic outcome of 72 patients with acute myeloblastic leukemia (FAB M1) were investigated. The patients were divided into two groups according to myeloperoxidase-(MPO) positive percentage of blast cells, namely a low (less than 50%) and high (greater than 50%) MPO group. No remarkable morphological difference of blast cells between these two groups was observed. The 38 patients with low MPO showed a significantly lower complete response rate (CR) (52.6%) than the 34 patients with high MPO (85.3%) (p = 0.003) that included 10 CAE-positive patients and 2 ANAE-positive CAE-negative patients. The low MPO group included 5 CAE-positive patients with granulocyte dysplasia and 7 additional patients with alpha naphthyl acetate esterase (ANAE) positivity who were chloroacetate esterase (CAE) negative. Low positivity of blast cells may be due to a defective enzyme expression in the former but also may be a reflection of 'monocytic' aberrant expression in the latter. The low MPO group in M1 with this heterogeneous population is less likely to achieve CR with chemotherapy, while the high MPO group with a higher CR rate suggests a more pure entity within the myeloblastic leukemias referred to as M1. After further refinement by eliminating 24 cases that were 'esterase positive' (ANAE and/or CAE), the results were still the same, suggesting that the more immature blast populations were in the low MPO group.

This study reports the cytochemical, electrophoretic and immunological characteristics of blasts cells from 39 cases of acute myelomonocytic leukaemia (M4). The results indicate considerable cytochemical heterogeneity, particularly with respect to esterase (alpha naphthyl acetate and chloroacetate) activities and suggest that an increased serum lysozyme concentration is a more consistent feature. Investigations with a range of monoclonal antibodies also revealed some differences in expression of monocyte-associated determinants although it is considered that immunological assessments are more consistent than cytochemistry in the detection of monocytic blast cell components. Analysis of ANAE isoenzymes by isoelectric focusing was found to be of particular value in cases where interpretation of ANAE cytochemistry was difficult.

A series of monoclonal antibodies reactive with normal myeloid cells at different stages of differentiation (anti-MY4, -MY7, -MY8, -Mo1, -Ia) were used to characterize the leukemic cells of 70 patients with acute myeloblastic leukemia (AML). Sixty-two of the leukemias expressed a phenotype corresponding to a recognizable immature normal myeloid cell. These 62 cases could be divided into 4 phenotype groups, corresponding approximately to the normal CFU-C (group I, 21%), myeloblast (group II, 26%), promyelocyte (group III, 8%), and promonocyte (group IV, 45%). Morphological subtyping of these leukemias tended to agree with the immunologic phenotype, particularly with more "differentiated" morphological subtypes, such as acute monocytic leukemia or acute promyelocytic leukemia. However, each phenotype group contained more than one morphological type of AML, indicating that the level of differentiation of the surface membrane of AML cells may not always be concordant with morphology. The phenotype groups were also analyzed with respect to cytochemical staining patterns, age, the presence of Auer rods, and complete remission rates. Statistically significant differences among the groups were noted in the distribution of myeloperoxidase staining, nonspecific esterase staining, and Auer rods. The complete remission rates varied from 60% (groups III and IV) to 88% (group II). These results suggest that surface marker analysis in AML may be used as a highly reproducible classification system that will provide additional information about the leukemic cells in conjunction with morphological analysis.

Four cell lines were established from peripheral blood of patients with leukemia. All lines express the Epstein--Barr virus nuclear antigen (EBNA) and therefore should be classified as lymphoblastoid cell lines. However, one of the lines UHKT-5 established from a patient with acute myelomonocytic leukemia has some features not typical for lymphoblastoid cell lines. The cells resemble to macrophages with the phagocytic ability for yeasts, strong alpha-naphthylacetate esterase positivity in phagocytizing cells and unusually long villi. Another line UHKT-7 established from a patient with hairy cell leukemia expresses the same isotype of membrane immunoglobulins as the original hairy cells.