Immunophenotypic, genomic and clinical characteristics of blast crisis of chronic myelogenous leukaemia

Myeloid Blast Crisis of Chronic Myeloid Leukemia Followed by Lineage Switch to B-Lymphoblastic Leukemia: A Case Report

Lineage switch is very rare in blastic crisis of chronic myeloid leukemia (CML-BC). Here, we report a case of CML-BC in which the blast lineage switched from myeloid to B-lymphoid. A 35-year-old male was initially admitted to our hospital because of abdominal distention for over a year and dizziness for one week. Prior to presentation at our hospital, he visited a local hospital because of abdominal distention where his white blood cell count and bone marrow (BM) smear indicated CML. Results from peripheral blood (PB) counts, bone marrow analysis, immunophenotyping by flow cytometry, and the detection of the Philadelphia chromosome were consistent with a diagnosis of myeloid blast crisis from CML. The patient received chemotherapy with imatinib for induction, which diminished the number of blasts. However, after three months, the blasts were increased in the PB and BM. The BM study and immunophenotyping by flow cytometry revealed B-lymphoblastic leukemia. In accordance with his first admission, a chromosome study revealed a karyotype of 46, XY, t(9; 22)(q34; q11) in all 20 cells analyzed, and B-lymphoblastic transformation from CML was diagnosed. Despite three months of treatment with DVCP (daunorubicin, vincristine, cyclophosphamide and prednisone) chemotherapy in combination with dasatinib, the patient did not achieve complete remission. The patient decided to stop treatment and was discharged from the hospital for financial reasons. This case implicates the Philadelphia chromosome with p210 BCR-ABL1 fusion proteins as a key molecule in CML-BC. Further research is needed to assess the frequency, treatment, and prognosis of CML-BC patients with lineage switch.

Standard treatment of Ph+ CML in 2010: how, when and where not to use what BCR/ABL1 kinase inhibitor?

Chronic myeloid leukaemia (CML) is a haematopoietic neoplasm characterised by the BCR/ABL1 oncoprotein. In chronic phase CML, the neoplastic clone exhibits multilineage differentiation and maturation capacity. The BCR/ABL1 kinase blocker imatinib shows major antileukaemic effects in most patients and is considered standard frontline therapy. However, not all patients have a long-lasting response to imatinib. Notably, resistance to imatinib has been recognised as an emerging problem and challenge in CML. Whereas CML stem cells are considered to exhibit intrinsic resistance, acquired resistance may, in addition, develop in subclones over time, resulting in an overt relapse. A key trigger of resistance in subclones are BCR/ABL1 mutations. For such patients, novel multikinase inhibitors such as nilotinib, dasatinib, bosutinib or bafetinib, which block the kinase activity of various BCR/ABL1 mutants, have been developed and reportedly exert antileukaemic effects in drug-resistant cells. For highly resistant patients, haematopoietic stem cell transplantation is an alternative option. Treatment decisions and the selection of drugs are based on the presence and type of BCR/ABL1 mutation(s), phase of disease, other disease-related variables and patient-related factors including age, compliance and co-morbidity. The current review provides an overview on standards in the diagnosis and therapy in CML, with special reference to novel BCR/ABL1 inhibitors.

Chronic myelogenous leukemia showing biphenotypic blast crisis followed by lineage switch to B lymphoblastic leukemia

Lineage switch is a very rare event in blastic crisis of chronic myelogenous leukemia (CML-BC). To our knowledge, only three cases of lineage switch between lymphoid and myeloid/myelomonocytic lineages have been reported in the literature. Here, we report a novel case of imatinib-resistant CML-BC, in which the blast lineage switched from biphenotypic to B-lymphoid.

The spectrum of adult B-lymphoid leukemias with BCR-ABL: molecular diagnostic, cytogenetic, and clinical laboratory perspectives

The Philadelphia (Ph) chromosome is characteristic of chronic myelogenous leukemia (CML), but it is also the most frequent cytogenetic abnormality in precursor B-lymphoblastic leukemia (ALL) of adults. The vast majority of CML patients have a BCR-ABL translocation that yields a 210 kD (p210) oncoprotein, whereas adult Ph-positive ALL cases can present with either a p190 or a p210 oncoprotein, or both. Considering that 30% of the patients with CML that progress to blast crisis will have a lymphoblastic presentation, adults presenting with a p210 ALL may have either a de novo ALL or CML presenting for the first time in lymphoblastic phase. To identify the distinguishing features, cases of p190-ALL, p210-ALL, and lymphoblastic CML were compared. In spite of significant overlap between the three entities, a number of features were found to aid in their differentiation. p210-ALL patients present at a younger age with blasts that frequently show loss of expression of CD34, whereas p190-ALL patients present with marked increase in peripheral blast percentage. Interestingly, bone marrow findings characteristic of a myeloproliferative disorder are specific, but are not sensitive for lymphoblastic CML. This study suggests that despite the similarities between these leukemias, p190-ALL, p210-ALL, and lymphoblastic phase CML likely represent three distinct diseases.

Concurrent megakaryocytic and erythroid chronic myelogenous leukemia blast crisis

Chronic myelogenous leukemia with blast crisis is seen in 15% to 20% of patients with chronic myelogenous leukemia. Chronic myelogenous leukemia with either erythroid or megakaryocytic blast crisis is not uncommon in the clinical setting. The incidence ranges from 0% to 33% in accordance with literature reports. The diagnosis of erythroid or megakaryocytic blast phase is often challenging because the percentage of blasts in the blood or bone marrow required for diagnosis has not been firmly established. Also, some myeloblasts can have aberrant expression of either erythroid or megakaryocytic markers by flow cytometry during clonal evolution. Early recognition of this entity is crucial because either megakaryocytic or erythroid blast crisis predicts an aggressive clinical course. To our knowledge, the coexistence of megakaryocytic and erythroid blasts has not been reported. We report a unique case of chronic myelogenous leukemia with this rare bilineage blast crisis in the background of dysplasia and marked myelofibrosis. Related literature is also reviewed.

[Erythroleukemic blast crisis of chronic myeloid leukemia.]

Erythroleukemic blast crisis of chronic myeloid leukemia (CML) is very rare. We report two cases of erythroleukemic blast crisis of CML resistant to imatinib treatment. Both patients made a rapid progression to blast crisis 6 and 4 months after diagnosis while being treated with imatinib 400 mg/day. Bone marrow aspiration revealed predominant erythroid precursors with 65.4% and 54.8% each. There were significant proportions (more than 20%) of myeloblasts among non-erythroid cells. Immunophenotyping revealed expression of glycophorin A confirming erythroleukemic blast crisis. The karyotyping result of patient 1 was 46,XX,t(9;22)(q34;q11.2)[3]/52,idem,+8,+12,+18,+21,+22,+der(22)t(9;22)[17] and that of patient 2 was 46,XX,inv(3)(q21q26.2),t(9;22)(q34;q11.2)[20]. Patient 1 showed no response to imatinib and BMS-354825 in the following bone marrow study. She died of septic shock as a complication of an infection after 69 days of blast crisis. Patient 2 received allogeneic bone marrow transplantation (BMT) in the cytogenetically no response state, but she also died of graft-versus-host disease 9 weeks after BMT. The poor prognosis and rapid progression of disease in both cases were correspondent to most of the reported cases. During the course of the disease of the two patients, we monitored the BCR-ABL chimeric mRNA with real-time quantitative polymerase chain reaction (RT-PCR), and it was found useful in predicting the imatinib response and progression to blast crisis of CML. Although both of our cases showed the typical bad prognosis and findings of erythroleukemic blast crisis of CML, the karyotypes were different from the expected type of t(3;21)(q26;q22). But the relationship between additional changes of EVI1 on chromosome 3q26 shown in case 2, and progression to the erythroleukemic blast crisis need further investigation.

Detection of BCR/ABL fusion product in normoblasts in a case of chronic myelogenous leukemia

Erythroblast phase of chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive acute erythroid leukemia are rare events. The distinction between these two entities is poorly defined. The World Health Organization (WHO) classification requires the presence of more than 50% of erythroblasts in the bone marrow for the diagnosis of both the erythroid/myeloid or pure erythroid subtypes of acute erythroid leukemia. However, in previous studies of erythroblast crisis CML, the percentage of erythroid series in the bone marrow is seldom mentioned and the direct relationship of the erythroblasts and the Philadelphia chromosome has never been established. We report a well-documented case of acute erythroid leukemia transformed from CML. The studies in morphology, immunohistochemistry, and flow cytometry fulfill the WHO criteria for the diagnosis of acute erythroid leukemia, and yet the complex karyotype containing Philadelphia chromosome indicates genetic evolution. Finally, the direct demonstration of the BCR/ABL fusion product by fluorescence in situ hybridization in the erythroblasts provides concrete evidence that the erythroblasts are part of the leukemic process and not an innocent bystander.

Megakaryocytic blast crisis as a first presentation of chronic myeloid leukemia

Acute megakaryocytic leukemia (AmegL) corresponds to 5.0-10.0% of all acute myeloid leukemias (AML). Blast crisis as the first presentation of chronic myeloid leukemia (CML) accounts for 10.0% of all cases.

OBJECTIVE

We report a case of megakaryocytic blast crisis as the first presentation of CML.

CASE REPORT

A 25-yr-old-female with a 2-month history of dry cough and a large, non-tender splenomegaly was found to have a hemoglobin concentration of 10.5 g/dL, a hematocritof 33.0%, a white blood cell count (WBC) of 11.4 x 106 L with 38% small blasts, eosinophilia of 5%, basophilia of 8%, and a platelet count of 580 x 109 L. Bone marrow aspiration revealed 24% of blast cells with cytoplasmatic blebs and hyperplastic megakaryocytic lineage with dysplasia. Cytochemical stains were all negative, immunophenotyping studies showed CD41 and CD61 positivity in blast cells. Bone marrow biopsy showed grade II fibrosis. Karyotype revealed 46, XX, t(9,22) (q34.1;q11.2)[20] and the reverse-transcriptase-PCR (RT-PCR) gave rise a product with a size corresponding to the 210 kDa protein (p210). No matched donor was found. After induction therapy 5.9% of blast cells persisted. The patient received Imatinib Mesylate and is doing well after a 12-month follow-up.

DISCUSSION

AmegL as the first presentation of CML is a rare and often fatal event. Some characteristics point towards the diagnosis of a blast crisis instead of AmegL de novo with t(9,22).

Double Ph-positive megakaryoblastic transformation of chronic myeloid leukemia

A 64-yr-old Japanese man presented with mild anemia, leukocytosis, and thrombocytosis in November 1999. A diagnosis of chronic myeloid leukemia was made with a positive Ph chromosome, and interferon alpha treatment was started, 6 million units a day. Two years later, in October 2001, the patient developed leukocytosis, an increased LDH level, and large blasts with basophilic cytoplasm with cytoplasmic projections appeared in the peripheral blood. Bone marrow aspiration revealed increased blasts (59.6%). These blasts were negative on peroxidase stain, positive on acid phosphatase, and weakly positive on alpha naphthyl butyrate esterase stain and periodic acid-Schiff stain. Immunohistochemical staining with monoclonal antibodies revealed that these blasts were strongly positive with anti-CD41 (glycoprotein IIb/IIIa), weakly positive with CD7, CD33, and CD34, and negative with other monoclonal antibodies. A diagnosis of megakaryoblastic transformation from chronic myeloid leukemia was therefore made. Two-color fluorescence in situ hybridization (FISH) for portions of the major-bcr and abl genes from bone marrow cells revealed two fused signals in 90.6% and one fused signal in 5.8% of 106 cells. A cytogenetic study revealed that bone marrow cells were 69, XYY, +6, -7, +8, -9, t(9;22)(q34;q11), +11, +13, -15, -16, dic(17;18)(p11;p11), -18, +19, +21, der(22)t(9;22) in six of nine examined cells. These findings confirmed that these megakaryoblasts originated from megakaryocytes of the chronic myeloid leukemia clone.

Novel therapies for chronic myelogenous leukemia

The BCR-ABL oncogene is essential to the pathogenesis of chronic myelogenous leukemia, and immune mechanisms play an important role in control of this disease. Understanding of the molecular pathogenesis of chronic myelogenous leukemia has led to the development of several novel therapies, which can be broadly divided into therapies based on 1) inhibition of the BCR-ABL oncogene expression, 2) inhibition of other genes important to the pathogenesis of chronic myelogenous leukemia, 3) inhibition of BCR-ABL protein function, and 4) immunomodulation. We have systematically reviewed each of these novel therapeutic approaches in this article.

CD56+ blastic transformation of chronic myeloid leukemia involving the skin

We report on two patients with chronic myeloid leukemia (CML) who presented blastic transformation involving the skin, with leukemic infiltrates showing unusual morphologic and immunohistologic characteristics. Both patients were elderly men with a 36-month and a 40-month history of CML, respectively. They presented with disseminated, reddish to violaceous papules and plaques (case 1), and with localized reddish nodules on the left temporal area (case 2). Concurrent features of blastic transformation in the bone marrow were observed in one patient (case 1). Histopathologic examination of skin lesions revealed similar features in both cases. There was a moderate to dense dermal infiltrate composed mainly of medium-sized atypical mononuclear myeloid precursor cells with only few relatively well-differentiated cells of the granulocytic series. Histochemical staining for naphthol-ASD-chloroacetate esterase revealed strong positivity (>50% of neoplastic cells) in case 2 and only scattered positivity (< 10% of neoplastic cells) in case 1. Immunohistologic analysis performed on paraffin-embedded sections showed in both cases variable reactivity of neoplastic cells for leucocyte common antigen (CD45), lysozyme, myeloperoxidase, CD11c, CD15, CD43, CD66, CD68, HLA-DR, and the neural cell adhesion molecule (NCAM) CD56. A negative reaction was observed for CD3, CD34, and TdT. The immunohistologic findings were remarkably similar to those reported for acute myeloid leukemia (AML) with monocytic differentiation (French-American-British [FAB] classification, subtype M4). Examination of blasts from the bone marrow performed in one patient (case 1) revealed a similar phenotype also with CD56 expression. In conclusion, our observations show that specific cutaneous infiltrates in CML may show morphologic and immunohistochemical characteristics similar to those observed in AML with monocytic differentiation. Moreover, specific cutaneous manifestations of CML may express CD56.

Chronic myeloid leukemia with minor-bcr breakpoint developed hybrid type of blast crisis

Although a breakpoint in the minor breakpoint cluster region (m-bcr) of the BCR gene is observed in about two-thirds of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia, this type of genomic rearrangement occurs very rarely in chronic myeloid leukemia (CML). We describe here the eighth case of m-bcr CML, and delineate unique clinical characteristics found in common to the 7 cases reported previously. Monocytosis with a low neutrophil/monocyte ratio resembling chronic myelomonocytic leukemia was the most striking feature of m-bcr CML. Splenomegaly and basophilia were not conspicuous in chronic phase. A high percentage of immature granulocytes and low neutrophil alkaline phosphatase score were the findings in common with classical CML. Lymphoid and myeloid blast changes have been observed at and shortly after presentation so far. We found a hybrid type of blast crisis in the course of m-bcr CML.Thus, m-bcr CML may be a definite subtype of CML, exhibiting distinct clinical characteristics. The presence of fusion product of m-bcr mRNA in an earlier myeloid cell may involve monocytic lineage in addition to myeloproliferative defects.

'Lymphoid' blast crisis of chronic myeloid leukaemia is associated with distinct clinicohaematological features

It has been suggested that in blast crisis (BC) of chronic myeloid leukaemia (CML) the clinical and laboratory features of patients with 'lymphoid' phenotype differ from those of patients with non-lymphoid BC. In order to assess any differences, 97 patients consecutively diagnosed with BC that followed a known chronic phase of CML were analysed. 19 patients had 'lymphoid' BC: in 17 the blasts expressed a B-lineage phenotype: in the remaining two they corresponded to T lymphoblasts. Four cases of B-lineage phenotype BC were considered as biphenotypic, due to the co-expression of myeloperoxidase and one or two other myeloid markers (CD33, CD13 and CD68) on the blast cells; in the other six cases of B-lineage BC the blasts expressed one or both of the myeloid markers CD33 (n = 4) and CD13 (n = 3). Patients with 'lymphoid' BC seldom had an accelerated phase prior to BC (1/19 v 36/78 with non-lymphoid BC, P = 0.002), had less frequent splenomegaly (9/19 v 59/78, P = 0.03) and hepatomegaly (5/19 v 45/78, P = 0.02) and showed a higher degree of marrow blast infiltration (mean value 74 +/- 24% v 38 +/- 23%, P < 0.0001), lesser blood basophilia (2.2 +/- 2.5% v 8.2 +/- 7.8%, P < 0.0001), and higher serum albumin levels (P = 0.001) than those with non-lymphoid BC. 13 patients with 'lymphoid' BC (68.4%) showed a favourable response to chemotherapy regimens including vincristine and prednisone and, overall, 'lymphoid' BC patients survived significantly longer than the remainder (median survival 12 months v 4.7 months, P = 0.006). These results indicate that 'lymphoid' BC of CML has a distinct clinicohaematological profile and confirm the better prognosis of such patients.

Burkitt-like blast crisis in chronic myeloid leukemia

A case of Burkitt-like blast crisis in a patient with chronic myelocytic leukaemia (CML) is presented. To our knowledge, this is the first such case recorded to date. The patient had a useful response to combination chemotherapy.

Immunophenotype and ultrastructural studies in blast crisis of chronic myeloid leukemia

Thirty-four patients with chronic myeloid leukemia in blast crisis (CML-BC) were evaluated for lineage differentiation with immunological markers and the presence of ultrastructural peroxidase. Eighteen (52.9%) were found to have myeloid blast crisis. Cytochemically, myeloperoxidase (MPO) could be detected only in six patients on light microscopy while in the remaining 12 patients, myeloid differentiation was confirmed only by demonstration of MPO either at ultrastructural level or by the reactivity with anti myeloperoxidase (anti MPO) antibody. Six (17.6%) had lymphoid blast crisis as identified by lymphoid specific markers (CD19; CD10; CD7; CD4) along with the absence of myeloid markers. Heterogenous blast cell populations with mixed lineage differentiation were seen in 4 (11.7%) patients. These cases showed both lymphoid (CD19, CD10) and myeloid (anti MPO and ultrastructural MPO) characteristics. A single case of megakaryoblastic blast crisis was identified with positivity for CD41 and CD42 along with the presence of platelet peroxidase at the ultrastructural level. Five cases (14%) of CML blast crisis remained unclassifiable. These results suggest that blast crisis in CML show an arrest of differentiation at an early stage when compared to de novo acute leukemias. This is particularly evident from the fact that MPO could only be demonstrated ultrastructurally or with anti MPO antibody in the majority of patients with myeloid differentiation. It is expected that utilisation of molecular studies including immunoglobulin and T-cell receptor gene rearrangement and m-RNA expression for myeloperoxidase will provide a better insight into the level of differentiation for the presently unclassifiable cases of CML-blast crisis.

Biotherapy of chronic myelogenous leukemia

The aim of this review is to summarize the current knowledge on the clinical results of biotherapy of chronic myelogenous leukemia (CML) and potential mechanisms of the antitumor action of interferon alpha. IFN alpha treatment induces hematologic and cytogenetic remissions in patients with chronic phase CML. In addition, the duration of the chronic phase is prolonged by IFN alpha resulting in a significant survival benefit. In two randomized clinical trials this survival benefit was demonstrated in all chronic phase CML patients independent of their risk scores. Moreover, IFN treatment also delays the onset of clinical relapse after allogeneic bone marrow transplantation. The critical mechanisms of IFN action have not yet been identified. Both direct and indirect antiproliferative mechanisms have been described. In particular, differential regulation of growth promoting and growth inhibiting cytokines represents an attractive hypothetical mechanism of IFN action. Nevertheless, no leukemia specific IFN activities explaining cytogenetic remissions and/or delay of disease progression have been identified. Further research on that field are required to further improve biological CML therapies.

Flow cytometry in the diagnosis of cancer

Flow cytometry has rapidly expanded from basic research to clinical laboratories mainly due to its unique characteristics regarding cell analysis. Among the clinical uses of flow cytometry cancer represents one of the most relevant. Several applications of flow cytometry can currently be applied to the study of cancer, including the detection of tumour cell DNA aneuploidy, the analysis of tumour cell proliferation and the immunophenotyping of leukemias. Although standardized flow cytometry protocols for these applications are scanty, the clinical value has been clearly established. The presence of DNA aneuploidy and a high proportion of S-phase tumour cells have been associated with tumour malignancy and a poor prognosis. The immunophenotype of leukaemia is of great help both for the diagnosis and classification of chronic lymphoproliferative disorders and acute leukaemias, especially in acute lymphoblastic leukemia cases and the M0, M3-variant, M6 and M7 acute myeloblastic leukaemia subtypes. In addition, it allows the identification of relatively rare leukemia cases such as the biphenotypic and the Nk-cell lineage leukemias. The development of flow cytometry is continuously bringing new applications into the clinical laboratory in the area of cancer diagnosis.

Chronic granulocytic leukaemia presenting with an extramedullary T lymphoblastic crisis

A 33-year-old man presented with hepatosplenomegaly and lymphadenopathy. Bone marrow findings were consistent with Philadelphia-positive accelerated-phase chronic granulocytic leukaemia (CGL). Lymph node histology and immunhistochemistry were diagnostic of T lymphoblastic lymphoma. Molecular studies on lymph node DNA identified rearrangement within the major breakpoint cluster region (M-bcr), indicating a common clonal origin of CGL and the T lymphoblastic lymphoma. We report the second case where extramedullary T lymphoblastic crisis was the presenting feature of CGL.

Cytogenetic and immunogenotypic alterations of blast crisis cells in chronic myelogenous leukemia independently linked to immunophenotypic expression

Chronic myelogenous leukemia (CML) is a disease of the hematopoietic stem cells, which can differentiate into either B-lymphoid or myeloid cells, because most of them develop either lymphoid or myeloid blast crisis. Immunophenotypic, genotypic, and cytogenetic analyses of 22 patients (24 episodes) with Philadelphia (Ph) positive CML in blast crisis were performed to determine the genetic alterations of the blast crisis cells. In B-lymphoid blast crisis, all the five patients had immunoglobulin heavy-chain (IgH) rearrangements and most of them showed normal karyotypes. Among the five patients, T-cell receptor (TCR) genes were rearranged at the following occurrence rates: 20% in TCR-beta, 60% in TCR-gamma, and 40% in TCR-delta chain genes. A high incidence of additional chromosome changes was noted in patients with B-lymphoid/myeloid-mixed blast crisis, but about 80% of them had rearranged IgH and about 40% had TCR rearrangements. In contrast, most of the patients with non-lymphoid blast crisis showed further chromosomal abnormalities, including +8, +19, i(17q), and double Ph, and most of them had germline configurations of IgH and TCR-gamma chain genes. Notably, only one patient (dual lymphoid and myelomegakaryoblast crisis) in this group exhibited IgH rearrangement, and TCR-beta and TCR-delta rearrangements were also rarely noted. Rearrangement of the IgH gene in CML blast crisis might be linked to expression of lymphoid markers, especially CD19.

Comparison of clinical and biologic features between myeloid and lymphoid transformation of Philadelphia chromosome positive chronic myeloid leukemia

Analysis of clinical and biologic features of chronic myeloid leukemia (CML) in blast crisis (BC) was performed on 36 patients: 25 had myeloid and 11 had lymphoid transformation. The median duration from diagnosis to onset of BC was significantly shorter in patients with lymphoid BC (6 months) than in those with myeloid BC (41 months). Patients in lymphoid transformation showed better response to therapy and had a significantly longer median survival time after BC than patients with myeloid transformation (56% vs 0% and 10 months vs 4 months, respectively). The leukemic cells from all the patients with lymphoid BC showed B-cell immunophenotype, confirmed by the presence of immunoglobulin (Ig) heavy chain gene rearrangements in the five patients studied. Two of the eight patients with complete marker study expressed myeloid-associated antigens on the blasts. A high incidence of CD7 expression (7/17 or 41%) was found in patients with myeloid BC, but none of the patients who had DNA analysis showed rearrangement of T-cell receptor beta chain gene. Chromosomal abnormalities +8, +19, +21, and i(17q) were detected only in the patients with myeloid BC but not in those with lymphoid BC. Combined analysis of the patients in this series and those reported previously has revealed a statistically significant difference in the distribution of bcr breakpoints between myeloid and lymphoid BC: the bcr breakpoints in more than half of the patients with myeloid crisis were mapped to Zone 2 while those in patients with lymphoid crisis occurred most frequently in Zone 3.

Immunophenotypic characterisation of acute leukaemia after polycythemia vera

AIMS

To analyze the immunophenotype of blast cells in patients with acute leukaemia after polycythemia vera, together with the most relevant clinical and haematological disease characteristics.

METHODS

The immunophenotype was analysed in nine patients by immunofluorescence flow cytometry using a panel of 15 monoclonal antibodies. The DNA content of blast cells was determined using Vindelov's technique.

RESULTS

The most relevant clinical and haematological disease characteristics included: the presence of enlarged spleen and liver by 56% and 67%, respectively; a moderate degree of leucocytosis with thrombocytopenia while haemoglobin was normal in 50% of patients. All patients received alkylating agents or hydroxyurea, or both. Interestingly, the chronic phase in patients receiving this latter drug was shorter. All cases showed a myeloid phenotype, four of them reactive only to early myeloid antigens (CD13/33); in the remaining cases the blast cells displayed granulomonocytic (CD14+, CD15+), erythroid (CD71 ), or megakaryocytic (CD61+, CD41+) markers. Coexpression of lymphoid related antigens (CD7, TdT, or CD19) was also detected. The morphological assessment of blast cells agreed with the immunophenotyping in five out of the nine cases. Blast cells from all six patients analysed displayed a diploid DNA content and the proportion of S-phase cells ranged from 0.4% to 4%.

CONCLUSIONS

These findings suggest a pluripotential stem cell with myeloid commitment as the target cell of acute leukaemia after polycythemia vera.

Differentiation and multidrug resistance in response to drug treatment in the K562 human leukaemia cell line

The relationship between differentiation and P-glycoprotein expression in response to chemotherapeutic drugs was studied in the K562 human leukaemia cell line by treatment with low, but clinically achievable levels of vinblastine and epirubicin. Resistant sublines were easily generated with the multidrug resistant phenotype being expressed in response to drug treatment as low as 1 ng/ml vinblastine and 10 ng/ml epirubicin. These sublines showed stable but heterogeneous expression of P-glycoprotein as revealed by immunocytochemistry, and confirmed by cloning. This heterogeneity was maintained over 18 months with intermittent drug treatment. While selection for resistance induced erythroid and myeloid differentiation, expression of P-glycoprotein was not correlated with the stem cell antigen CD34 or with specific markers of erythroid or myeloid differentiation.

The relationship between the location of the breakpoint within the M-bcr and clinical parameters

The Philadelphia chromosome (t9;22)(q34;q11) is a characteristic abnormality in chronic myeloid leukemia. In greater than 95% of the cases, the breakpoint occurs with the M-bcr region of the BCR gene on chromosome 22. Several studies have attempted to correlate the location of the breakpoint within the M-bcr with a clinical parameter. The majority of studies have examined the relationship between the site of breakpoint and the median chronic phase duration (CPD). Some studies have reported a correlation, with 5' breakpoint patients who have a longer median CPD than patients with a 3' breakpoint. However, other groups have reported that no correlation exists. Furthermore, data from some of the latter groups have suggested that a correlation may exist with the lineage of blast crisis which developed and 3' breakpoint patients had a higher than expected number of lymphoid blast crisis. A correlation between high platelet counts at diagnosis and patients with a 3' breakpoint or those who expressed a b3-a2 BCR-ABL mRNA has also been described. No consistent conclusion from any of these studies can be drawn. This may due, in part, to some degree of patient and sample selection, although environmental, genetic or life-style factors may also contribute.