"Pure" monocytic or histiomonocytic leukemia: a revised concept

Diagnostic challenges in acute monoblastic/monocytic leukemia in children

Acute monoblastic/monocytic leukemia (AMoL), previously defined as M5 according to FAB classification, is one of the most common subtypes of Acute Myeloid Leukemia (AML) in children, representing ~15-24% of all pediatric AMLs. Currently, the characterization of monocytic-lineage neoplasia at diagnosis includes cytomorphology, cytochemistry, immunophenotyping by multiparametric flow cytometry, cytogenetics, and molecular biology. Moreover, measurable residual disease (MRD) detection is critical in recognizing residual blasts refractory to chemotherapy. Nonetheless, diagnosis and MRD detection may still be challenging in pediatric AMoL since the morphological and immunophenotypic features of leukemic cells potentially overlap with those of normal mature monocytic compartment, as well as differential diagnosis can be troublesome, particularly with Juvenile Myelomonocytic Leukemia and reactive monocytosis in infants and young children. A failure or delay in diagnosis and inaccuracy in MRD assessment may worsen the AMoL prognosis. Therefore, improving diagnosis and monitoring techniques is mandatory to stratify and tailor therapies to the risk profile. This Mini Review aims to provide an updated revision of the scientific evidence on pediatric AMoL diagnostic tools.

Monocytic leukemia in infancy. A review of eight children

The clinical and pathologic features of eight infants with monocytic leukemia are reviewed. The children were all aged 12 months or less at diagnosis and had a high incidence of extramedullary features, skin infiltration being particularly common. The diagnosis was established by conventional morphologic and cytochemical techniques. Using the French-American-British (FAB) classification, five infants had FAB 5a disease, and three had FAB 5b. The difficulties in making the diagnosis from extramedullary sites and the overlap that exists at this age between monocytic leukemia, true histiocytic lymphoma, and malignant histiocytosis are discussed. The treatments given to the group and their response are reviewed. Five of the patients received VP-16-213 and cyclophosphamide as primary induction chemotherapy, a combination that merits further evaluation in leukemia with monocytic features.

The value of immunoperoxidase studies in the diagnosis of 2 cases of acute leukaemia

2 cases of acute leukaemia in which the precise diagnosis was established using the immunoperoxidase technique on particle sections, a method not usually employed for acute leukaemias, are reported. Morphologically and cytochemically these cases were initially diagnosed as acute megakaryoblastic (case 1) and acute monocytic (case 2) leukaemia. Based on the immunoperoxidase studies, these diagnoses were corrected to DiGuglielmo's disease (case 1) and plasma cell leukaemia (case 2).

Tumours of the mononuclear phagocyte system: a review of clinical and pathological features

Cells of the mononuclear-phagocyte system (MPS) may give rise to a wide variety of tumours of diverse morphology ranging from acute leukemia to small benign tumours of the skin. This review of tumours of the MPS was prompted by recent advances in understanding of tumour morphology and immunologic features. It is now possible to differentiate tumours of the MPS mor precisely from tumours of lymphoid origin with which they have often been confused; however, controversy still exists as to the origin of the malignant cell of Hodgkin disease. Current evidence is reviewed which favours the view tht the malignant cell of Hodgkin disease is of monocyte origin. A classification of MPS tumours based on organ system of origin and disease extent is presented.

Acute monocytic leukemia: a surface marker study

Thirteen cases of acute monocytic leukemia (AMoL) were studied morphologically, cytochemically, and immunologically in an attempt to determine similarities and/or differences between acute monocytic and lymphocytic leukemias. Single class surface immunoglobulins (IgG kappa) were seen in six cases. These markers are thought to represent serum immunoglobulins attached to the leukemic monocytes via the receptors for the Fc portion of immunoglobulin and are not synthesized by the cells as is the case with B lymphocytes. Receptors for complement were also noted. It appears that surface immunoglobulins and receptors for the Fc portion of the immunoglobulin and complement, which are found on several classes of normal lymphocytes and monocytes, may also be found on leukemic monocytes. Antisera to B lymphocytes, detecting HlA-DRw antigens, also reacted with some of the leukemic monocytes.

In vitro evidence for an unusual progenitor cell in acute monocytic leukemia

The peripheral blood of 2 patients with acute monocytic leukemia of the undifferentiated type was studied for the presence of leukemic progenitor cells in colony forming assays. The peripheral blood of both patients contained only one type of progenitor cell as determined with these assay systems. Daughter cells of these progenitor cells morphologically and histochemically resembled monoblasts and immature macrophages. Similar progenitor cells were not encountered in the study of 5 patients with acute myelogenous leukemia whose peripheral blood cells formed colonies in the same system. The finding of this unusual progenitor cell supports the existence of acute monocytic leukemia as a separate clinicopathologic entity, and suggests that it represents a malignant transformation of a progenitor cell of the monocyte/macrophage series. An alternative explanation of these observations would be provided by single phenotypic expressions of a multi-potent stem cell which has undergone malignant transformation.

Monocytic leukemias

The monocytic leukemias may be subdivided into acute monocytic leukemia, acute myelomonocytic leukemia, and subacute and chronic myelomonocytic leukemia. The clinical features of acute monocytic and acute myelomonocytic leukemias are similar and are manifestations of bone marrow failure. Gingival hypertrophy and skin infiltration are more frequent in acute monocytic leukemia. Cytomorphologically the blast cells in acute monocytic leukemia may be undifferentiated or differentiated, whereas in the acute myelomonocytic variety there are mixed populations of monocytic and myeloblastic cells. Cytochemical characteristics include strongly positive reactions for nonspecific esterase, inhibited by fluoride. The functional characteristics of acute monocytic and acute myelomonocytic cells resemble those of monocytes and include glass adherence and phagocytoses, the presence of Fc receptors for IgG and C'3, and the production of colony stimulating activity. Subacute and chronic myelomonocytic leukemias are insidious and slowly progressive diseases characterized by anemia and peripheral blood monocytosis. Atypical monocytes called paramyeloid cells are characteristic. The drugs used in the treatment of acute monocytic and acute myelomonocytic leukemias include cytosine arabinoside, the anthracyclines, and VP 16-213. Drug therapy in subacute and chronic myelomonocytic leukemias is not usually indicated, although VP 16-213 has been claimed to be effective.

Phagocytosis in acute leukemia

The phagocytic potential of leukemic cells in various types of acute leukemia was studied. Cases included lymphoblastic leukemia, myeloblastic leukemia, myelomonocytic leukemia, monocytic leukemia, progranulocytic leukemia, blast transformation of chronic myelocytic leukemia, and unclassified leukemias. Cytochemical stains were used as an aid in classification. These included Sudan black B, naphthol AS-D chloroacetate esterase, alpha-naphthyl butyrate esterase, acid phosphatase, and periodic acid-Schiff. Phagocytosis was evaluated after incubation of leukemic cells with Candida albicans. Rare phogocytic activity was seen in lymphoblastic leukemia, unclassified leukemias, blast crises in chronic myelocytic leukemia, and progranulocytic leukemia. Myeloblastic leukemias were feebly phagocytic. Myelomonocytic leukemia and monocytic leukemia both exhibited marked phagocytosis which distinguished them from the other acute leukemias. Myelomonocytic leukemia could be differentiated from acute monocytic leukemia by its greater phagocytic capacity.

Chronic myelomonocytic leukemia: light and electron microscopy of the bone marrow

Clinical data and light and electron microscopic findings are presented in a patient with chromic myelomonocytic leukemia of about 5 years' duration and no need for specific therapy. Cytogenetic studies failed to demonstrate a Philadelphia-chromosome. The leading clinical symptoms were anemia, moderate hepatomegaly, and leukocytosis with monocytes in the peripheral blood count. Light microscopy of bone marrow cores showed hypercellularity of neutrophil granulocytic and monocytic cell lines including some precursor forms. Electron microscopy confirmed the existence of a biphasic myelomonocytic cell proliferation with predominance of mature forms in both lineages; there were no gross cellular abnormalities and no "hiatus leukaemicus". Consupicuous were cells of an undeterminated origin apparently neither belonging to the neutrophil granulocytic nor monocytic series and large histiocytic cells, possibly corresponding to the so-called sea-blue histiocytes of light microscopy. The high degree of maturation of both cell lines in the bone marrow is in accordance with the relatively benign and prolongated course of this rare type of leukemia.

Acute monocytic leukemia in an irradiated Beagle

A purebred female Beagle dog that had received 2,000 R of protracted wholebody gamma-irradiation from 60Co when 14 months old had hematologic changes consistent with a myeloproliferative disorder 3 years after the termination of radiation exposure. Peripheral blood and bone marrow findings during the 7-month period before death showed progressive anemia with increased numbers of platelets; immature granulocytes, monocytes and promonocytes. A period of partial remission occurred during which time the peripheral blood was aleukemic, although there was marked thrombocytosis and abnormal erythropoiesis which was evidenced by bizarre circulating nucleated red cells, anisocytosis, poikilocytosis and Howell-Jolly bodies. The dog had a terminal crisis with marked leukocytosis, most cells in the peripheral blood being bizarre monocytes and promonocytes. Tissues obtained at necropsy showed diffuse as well as focal infiltration of the spleen, liver, lymph nodes, heart, kidney and gastrointestinal wall with immature neoplastic cells resembling monocytes and monocytic precursors. The monocytic differentiation of the invasive cell population was confirmed by morphological, cytochemical, histological, ultrastructural and in vitro cell culture studies.

Cytochemistry of esterases

Esterases are enzymes that cleave aliphatic and aromatic ester bonds. With the use of synthetic substrates, esterases can be demonstrated in hematopoietic cells. Using alpha naphthyl acetate or alpha naphthyl butyrate, nonspecific esterase activity can be demonstrated. Intense activity of nonspecific esterase that is inhibited by fluoride is characteristic of cells of monocytic or reticulum cell origin. Using naphthol ASD-chloroacetate, specific esterase activity can be detected. Specific esterase is a lysosomal enzyme and is a useful marker for cells of granulocytic origin. Distinctive patterns of specific and nonspecific esterase activities are found in marrow cells from patients with various types of hematologic disorders. With the use of electrophoretic techniques, isoenzymatic analysis of esterases can be achieved.

Leukemic phase of malignant histiocytosis (arguments in favour of the histiomonocytic origin of the abnormal cells)

A 15-year-old female was treated for malignant histiocytosis. The occurrence of a leukemic phase (178,000 blasts/cu mm) during the follow up provided the opportunity of studying a large number of malignant cells by cytochemical electron microscopic, and cell membrane markers techniques. Acid phosphatase reaction was strongly positive and totally inhibited by tartaric acid. Nonspecific esterase reaction was moderately positive with inhibition by sodium fluorid. Electron microscopy revealed the presence of surface membrane pseudopods and the phagocytic activity of the cells. The leukemic cells had a receptor for the Fc fragment of IgG. These findings support the histiomonocytic origin of the abnormal cells in malignant histiocytosis.

Nonspecific activation of complement by leukemic cells

Non-specific activation of complement (NAC) on cell membranes via the alternative pathway was studied by using leukemic cells and cells from a generalized reticulohistiocytosis. The cells were treated with normal human serum in veronal-buffered saline containing ethyleneglycoltetraacetrate and MG++. Since human erythrocytes (HuE) are known to adhere to complement-reacted cell membranes in an immune adherence reaction, complement activation on the cell membrane was confirmed by the rosette formation of HuE which is due to the generation of C3b molecules on the cell membrane. Only cells from Schilling-type acute monocytic leukemias and cells from a generalized reticulohistiocytosis possessed NAC ability. All other leukemic cells tested, as well as normal hematopoietic and lymphoreticular cells, were NAC-negative. Furthermore, none of the mitogens tested generated NAC ability on normal peripheral blood lymphocytes.

Morphological and immunological similarity of the monocytes from pure and mixed monocytic leukaemias

Morphological and immunological marker data on a patient with 'pure' monocytic leukaemia are presented and compared with those of 6 cases of clearly mixed myelomonocytic leukaemia with a variable monocytic component. In all patients studied, the leukaemic monocytes expressed a receptor for the Fc of IgG, and IgG sensitization markedly enhanced phagocytosis of ox erythrocytes. A variable, but lower, percentage of the leukaemic monocytes had a receptor for mouse C3, but the cells uniformly lacked surface immunoglobulin and receptors for the Fc of IgM and for unsensitised mouse erythrocytes. Cytochemical and ultrastructural study also showed no clear difference between the monocytes of the 'pure' and mixed monocytic leukaemias. This report therefore lends no support to the concept of distinct types of monocytic leukaemia.

The distinctive features of acute monocytic leukemia

Acute monocytic leukemia is an uncommon form of acute leukemia. Distinctive clinical features include gingival hypertrophy, lymphoadenopathy, coagulation disorders, and lysozymuria. Blast cell morphology and cytochemistry are diagnostic. Receptors for the Fc fragment of IgG have been demonstrated on the basis of a few cases. The drug VP 16-213 has been shown to be very effective in treatment of untreated and previously treated patients.

Cytochemical profile of human haematopoietic biopsy cells and derived cell lines

Twenty-three human haematopoietic cell lines, normal and mitogen stimulated peripheral blood lymphocytes and tumour material from fresh leukaemias, myelomas and lymphomas were investigated with a panel of cytochemical reactions. Normal and mitogen stimulated lymphocytes, non-neoplastic lymphoblastoid cell lines (LCL), lymphoma lines with B-lymphocyte characteristics, chronic lymphocytic leukaemia and fresh lymphocytic lymphomas reacted weakly or negatively with all stains. T-lymphocyte acute leukaemia lines were PAS and alpha-naphtyl acetate esterase positive. Myeloma lines and fresh myelomas were strongly beta-glucoronidase positive. A histiocytic lymphoma cell line was strongly esterase positive with naphtol AS-D acetate esterase inhibited by NaF. The three fresh histiocytic lymphomas, however, reacted as the lymphocytic lymphomas suggesting a lymphoid origin. A myeloid leukaemia line was strongly positive for acid phsophatase. No major disagreement was noted between the reactivity of established neoplastic lines and the corresponding fresh biopsy cells indicating an unaltered qualitative expression of enzyme production after prolonged in vitro culture.

Acute myelomomocytic leukemia terminating in histiocytic medullary reticulosis: cytochemical, cytogenetic and electron microscopic studies

A case of acute myelomonocytic leukemia terminating in histiocytic medullary reticulosis is reported. The evolution of a single cellular clone presenting with progressive change of the morphological features of the leukemic cells towards more anaplastic elements endowed with prominent phagocytic properties is suggested on the basis of both cytochemical and chromosomal data. The histiocytic nature of the malignant proliferating cells and platelet phagocytosis has been confirmed by electron microscopic investigation. The main pathogenetic explanations of the evolutionary patterns of the disease are discussed with relation to: a) involvement of a common stem cell giving rise to different proliferative patterns of cells in a multiphasic sequence; b) release of dysplastic platelets and defective erythrocytes with massive sequestration by histioid phagocytic cells; and c) coexistence of two different disorders.