Morphology of acute promyelocytic leukemia with cytogenetic or molecular evidence for the diagnosis: characterization of additional microgranular variants

Phenotypic clues that predict underlying cytogenetic/genetic abnormalities in myeloid malignancies: A contemporary review

Precise subclassification of myeloid malignancies per the World Health Organization (WHO) classification system and the International Consensus Classification of Myeloid Neoplasms and Acute Leukaemias (ICC) requires investigation and documentation of the presence of cytogenetic and/or molecular genetic changes. These ancillary studies not only help in diagnosis, but also the prognosis of disease; however, they take time to be completed. In contrast, morphological evaluation of material from the blood and bone marrow specimens of cases where myeloid malignancies are suspected is usually completed quickly. Cytomorphological assessment may predict genetic changes and can be helpful in triaging acuity. This is especially true in haematological emergencies such as acute promyelocytic leukaemia (APL), where prompt APL-specific therapy can be life changing. Similarly, some morphological clues may help identify core binding factor leukaemias where a diagnosis of acute myeloid leukaemia (AML) could be rendered without reaching the 20% blast cutoff with immediate treatment-decision implications, or even a subset of cases of AML with FLT3 ITD/NPM1 mutation(s) which show characteristic features. Even though FISH/cytogenetics and/or PCR are still required for establishing the final diagnosis, evaluation for the presence of specific cytomorphological features that help predict genetic changes can be a useful tool to help guide early therapy.

Oral Manifestation as the Main Sign of an Advanced Stage Acute Promyelocytic Leukemia

Acute myeloid leukemia is an aggressive malignant neoplasm occurring mainly in elderly, with the median age of 65 years. Oral manifestations, mainly spontaneous bleeding, are a common finding in acute myelocytic leukemia and may represent the initial evidence of the disease. This report describes a case of a 47-year-old man with a one-month history of spontaneous oral bleeding. The patient had already been consulted by two professionals but he remained undiagnosed. The physical examination revealed paleness, fever, epistaxis and ecchymoses in the oral mucosa. The complete blood count revealed anemia, severe thrombocytopenia and leukocytosis with blasts predominance, reinforcing the diagnosis hypothesis of an acute leukemia. The patient was immediately referred to the Hospital and despite having received a quick intervention, he died 3 days after the admission due to diffuse pulmonary alveolar hemorrhage. According to the peripheral blood immunophenotyping the diagnosis of hypogranular variant of acute promyelocytic leukemia was established. The delay in the diagnosis may have influenced the unfavorable outcome. Early diagnosis and management are indispensable for survival of leukemia patients. In this way, dentists may be responsible for an early detection of oral manifestations of leukemia and for a fast referral to an adequate professional.

High-Throughput Method for Automated Colony and Cell Counting by Digital Image Analysis Based on Edge Detection

Counting cells and colonies is an integral part of high-throughput screens and quantitative cellular assays. Due to its subjective and time-intensive nature, manual counting has hindered the adoption of cellular assays such as tumor spheroid formation in high-throughput screens. The objective of this study was to develop an automated method for quick and reliable counting of cells and colonies from digital images. For this purpose, I developed an ImageJ macro Cell Colony Edge and a CellProfiler Pipeline Cell Colony Counting, and compared them to other open-source digital methods and manual counts. The ImageJ macro Cell Colony Edge is valuable in counting cells and colonies, and measuring their area, volume, morphology, and intensity. In this study, I demonstrate that Cell Colony Edge is superior to other open-source methods, in speed, accuracy and applicability to diverse cellular assays. It can fulfill the need to automate colony/cell counting in high-throughput screens, colony forming assays, and cellular assays.

New strategies in acute promyelocytic leukemia: moving to an entirely oral, chemotherapy-free upfront management approach

Incorporation of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) into the management paradigms of acute promyelocytic leukemia (APL) has markedly improved outcomes. Significant progress occurred in understanding the molecular pathogenesis of APL. ATO, in contrast with ATRA, is capable of eradicating the APL-initiating cells and can result in cure. Preclinical and clinical data confirmed the synergy of ATO and ATRA, and the ATRA-ATO combination was proved noninferior to a standard ATRA-chemotherapy regimen in patients with non-high-risk APL. Oral formulations of arsenic exhibited excellent activity in advanced clinical testing and their combinations with ATRA offer an opportunity for a completely oral, chemotherapy-free regimen for curing APL. Nonetheless, significant challenges remain. Reducing early death due to bleeding complications is an important area of unmet need. Data suggest that delays in initiation of ATRA upon suspecting APL continue to occur in the community and contribute to early mortality. Questions remain about the optimal place and schedule of arsenic in the therapeutic sequence and the role of the oral formulations. Refining the role of minimal residual disease in directing treatment decisions is important. Development of novel targeted agents to treat relapsed disease requires deeper understanding of the secondary resistance mechanisms to ATRA and ATO.

Atypical features in a patient with acute promyelocytic leukaemia: a potential diagnostic pitfall

Acute promyelocytic leukaemia (APML) is a malignancy with a high cure rate; however, delay in diagnosis or treatment can result in morbidity and mortality. APML has characteristic clinical, morphological, immunophenotypic and molecular features. In patients with acute leukaemia, a high index of suspicion is required to exclude APML. Very rarely APML patients at diagnosis can demonstrate atypical features. We reported a patient whose bone marrow features resembled acute myeloid leukaemia with predominantly agranular blasts, devoid of Auer rods and expressing CD34 and HLA-DR on flow cytometry. APML was not suspected initially but after cytogenetic and molecular genetic studies demonstrated t(15;17), appropriate therapy with ATRA+ chemotherapy was instituted and the patient showed remarkable and sustained response to treatment. This case highlights the fact that morphology and immunophenotyping are useful but not infallible indicators for these malignancies and, ultimate diagnoses will require detection of the characteristic molecular markers.

Rapid detection of PML-RARA fusion gene by novel high-speed droplet-reverse transcriptase-polymerase chain reaction: possibility for molecular diagnosis without lagging behind the morphological analyses

BACKGROUND

Acute promyelocytic leukemia (APL) is an aggressive disease requiring prompt diagnosis and treatment. Rapid detection of the PML-RARA fusion gene provides the molecular basis for a highly effective therapy with all-trans retinoic acid. We developed a rapid assay by novel droplet-reverse transcriptase-polymerase chain reaction (droplet-RT-PCR) for the detection of the PML-RARA fusion gene in APL patients.

METHODS

RNA was extracted from 7 samples obtained from 5 APL patients with the PML-RARA fusion gene confirmed by nested RT-PCR and fluorescence in situ hybridization. Using these 7 samples, we evaluated the reaction time and amplification efficiency of the droplet-RT-PCR.

RESULTS

Using the droplet-RT-PCR, we could detect the PML-RARA fusion gene in all 7 samples. The reaction time for 50 cycles of droplet-RT-PCR was 27 min. The amplification by the droplet-RT-PCR assay was considered positive for the PML-RARA fusion gene in less than 22 min, at the point when the fluorescence exceeded the threshold level.

CONCLUSIONS

Our novel droplet-RT-PCR assay is specific for the detection of the PML-RARA fusion gene and has a markedly reduced reaction time. Thus, the novel droplet-RT-PCR assay contributes to the rapid diagnosis of APL without lagging behind the morphological assessment.

Usefulness of CD11a and CD18 in flow cytometric immunophenotypic analysis for diagnosis of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is an aggressive disease that requires prompt diagnosis and therapy. Flow cytometry immunophenotyping can serve as a screening test for APL before the results of cytogenetic or molecular testing for t(15;17)(q22;q21)/PML-RARα are often dimly expressed or absent in APL. We used flow cytometry immunophenotyping with an antibody panel including CD11a and CD18 to assess 36 APL and 33 other AML cases. HLA-DR, CD11a, and CD18 were absent in 81% of APL and 12% of other AML cases (specificity, 88%). By further including combinations of HLA-DR-, CD2+, and either CD11a- or CD18-, we identified 92% of APL cases with 85% specificity. These data compare favorably with the combination of HLA-DR-, CD34-, and CD117+ for APL diagnosis, which had a sensitivity of 64% in this study.

FLT3/ITD associated with an immature immunophenotype in PML-RARα leukemia

Acute promyelocytic leukemia (APL) is characterized by the specific PML-RARα fusion gene resulting from translocation t(15;17) (q22;q12). Internal tandem duplication (ITD) of the FLT3 gene has been observed in approximately 35% of APLs, and large-scale studies have identified the presence of ITD as an adverse prognostic factor for acute myeloblastic leukemia (AML) patients. Aberrant expressions of surface antigens, such as CD2, CD34, and CD56, have been found in APL, but the implications of this are not well understood. We investigated the incidence of the FLT3/ITD mutation and FLT3/D835 (I836) point mutation in 25 APL patients. Incidence ratios of FLT3/ITD, D835 (I836), and both FLT3/ITD and D835 (I836) were 36%, 36% and 8%, respectively. FLT3/ITD⁺ cases showed a predominance of the bcr3 isoform (P=0.008) and M3v morphology (P<0.001). We found that all FLT3/ITD⁺ cases expressed CD2 (9 of 9) more frequently than that of FLT3/ITD⁻ (1 of 16) (P<0.001), while only one of the CD2⁺ cases (1 of 10, 10%) did not harbor FLT3/ITD, and all CD2⁺CD34⁺ cases (5 of 5, 100%) harbored FLT3/ITD. In addition, quantitative polymerase chain reaction analysis showed that FLT3 mRNA was more abundantly expressed in FLT3/ITD⁺ than that in FLT3/ITD⁻ (P=0.025), while there was no difference between D835(I836) ⁺ and D835(I836)⁻ with regards to aberrant surface-antigen expression, expression levels of FLT3 mRNA, M3v morphology, and the bcr3 isoform of PML-RARα mRNA. This study demonstrates that the presence of FLT3/ITD, but not D835 (I836), is closely related to aberrant CD2 expression and high expression levels of FLT3 mRNA. Our findings also suggest that FLT3/ITD as a secondary genetic event may block differentiation at the immature stage of APL.

Thromboembolic and bleeding complications in acute leukemia

The risk of both thromboembolic and bleeding complications is high in acute leukemia. This double hazard has a significant negative impact on the morbidity and mortality of patients with this disease. The clinical manifestations of both complications show special features specific to the form of acute leukemia. Recognition of these characteristics is important in the diagnosis and management of acute leukemia. In this article, several additional issues are addressed, including the features of bleeding and thrombosis in acute promyelocytic leukemia, the current understanding of the leukostasis syndrome and the iatrogenic complications including catheter-associated thrombosis, and the adverse effects of therapeutic agents used in acute leukemia. As regards the bleeding complications, thrombocytopenia is a major cause. Corrective measures, including recent guidelines on platelet transfusions, are provided.

Recent advances in the diagnosis and management of childhood acute promyelocytic leukemia

Since the successful introduction of all-trans-retinoic acid (ATRA) and its combination with anthracycline-containing chemotherapy, the prognosis for acute promyelocytic leukemia (APL) has markedly improved. With ATRA and anthracycline-based-chemotherapy, the complete remission rate is greater than 90%, and the long-term survival rate is 70-89%. Moreover, arsenic trioxide (ATO), which was introduced for APL treatment in 1994, resulted in excellent remission rates in relapsed patients with APL, and more recently, several clinical studies have been designed to explore its role in initial therapy either alone or in combination with ATRA. APL is a rare disease in children and is frequently associated with hyperleukocytosis, which is a marker for higher risk of relapse and an increased incidence of microgranular morphology. The frequency of occurrence of the promyelocytic leukemia/retinoic acid receptor-alpha (PML/RARα) isoforms bcr 2 and bcr 3 is higher in children than in adults. Although recent clinical studies have reported comparable long-term survival rates in patients with APL, therapy for APL in children is challenging because of the risk of early death and the potential long-term cardiac toxicity resulting from the need to use high doses of anthracyclines. Additional prospective, randomized, large clinical trials are needed to address several issues in pediatric APL and to possibly minimize or eliminate the need for chemotherapy by combining ATRA and ATO. In this review article, we discuss the molecular pathogenesis, diagnostic progress, and most recent therapeutic advances in the treatment of children with APL.

Does microgranular variant morphology of acute promyelocytic leukemia independently predict a less favorable outcome compared with classical M3 APL? A joint study of the North American Intergroup and the PETHEMA Group

Few studies have examined the outcome of large numbers of patients with the microgranular variant (M3V) of acute promyelocytic leukemia (APL) in the all-trans retinoic acid era. Here, the outcome of 155 patients treated with all-trans retinoic acid-based therapy on 3 clinical trials, North American Intergroup protocol I0129 and Programa para el Estudio de la Terapéutica en Hemopatía Maligna protocols LPA96 and LPA99, are reported. The complete remission rate for all 155 patients was 82%, compared with 89% for 748 patients with classical M3 disease. The incidence of the APL differentiation syndrome was 26%, compared with 25% for classical M3 patients, and the early death rate was 13.6% compared with 8.4% for patients with classical M3 morphology. With a median follow-up time among survivors of 7.6 years (range 3.6-14.5), the 5-year overall survival, disease-free survival, and cumulative incidence of relapse for patients with M3V were 70%, 73%, and 24%, respectively. With a median follow-up time among survivors of 7.6 years (range 0.6-14.3), the 5-year overall survival, disease-free survival, and cumulative incidence of relapse among patients with classical M3 morphology were 80% (P = .006 compared with M3V), 81% (P = .07), and 15% (P = .005), respectively. When outcomes were adjusted for the white blood cell count or the relapse risk score, none of these outcomes were significantly different between patients with M3V and classical M3 APL.

A variant acute promyelocytic leukemia with t(11;17) (q23;q12); ZBTB16-RARA showing typical morphology of classical acute promyelocytic leukemia

A subgroup of acute leukemia with morphology resembling acute promyelocytic leukemia (APL) shows variant translocations involving RARA and has a different morphology from that of classical APL. The variant APL with t(11;17)(q23;q12); ZBTB16-RARA subgroup has been reported to have leukemic cells with regular nuclei, many granules, absence of Auer rods, an increased number of Pelgeroid neutrophils, strong myeloperoxidase (MPO) activity, and all-trans-retinoic-acid (ATRA) resistance. Here, we report a case of variant APL with t(11;17)(q23;q12); ZBTB16-RARA showing typical morphological features of classical APL, including numerous Auer rods and faggot cells. The leukemic cells expressed CD13, CD33, CD117, human leukocyte antigen (HLA)-DR, and cytoplasmic-MPO on the immunophenotyping study. The diagnosis was confirmed by cytogenetic and molecular studies. To distinguish variant APL cases from classical APL cases, regardless of whether morphologically the findings are consistent with those of classical APL, combining morphologic, immunophenotypic, cytogenetic, and molecular studies before chemotherapy is very important.

Genetic Analyses Permit the Differentiation Between Reactive Malfunctions (‘Promyelocyte Arrest’) and Arising Promyelocyte Leukemia in a Pregnant Patient With a History of a Medulloblastoma

We report the case of a 24-year-old woman with a history of radiotherapy for a cerebellar medulloblastoma 2 years prior to detection of a lymph node metastasis of the former disease and a pancytopenia in the peripheral blood. On bone marrow (BM) examination promyelocyte leukemia vs. a reactive 'promyelocyte arrest' were discussed. The translocation t(15;17) was found in some nuclei and there was a PML-RARalpha gene rearrangement detectable by RT-PCR. Furthermore, there was BM infiltration by the primary cancer. All these results led to the diagnosis of a relapse of the medulloblastoma and of a beginning promyelocyte leukemia. As the patient was pregnant, she had to be parted with the baby to facilitate intensive chemotherapy. She did not respond to a therapeutic regimen specific for promyelocytic leukemia but achieved complete remission of the medulloblastoma as well as the leukemia after the administration of polychemotherapy specific for medulloblastoma. One year later, she suffered from a relapse of her leukemia. Now nearly all cells showed a t(15;17) aberration. Immunophenotype analyses showed a shift to a more undifferentiated blast phenotype that was, however, still HLA-DR negative. The patient again received chemotherapy for leukemia but developed a sepsis 3 months later and died of pancytopenia ensuing her leukemia. There was no clinical evidence for recurrence of the medulloblastoma.

The coagulopathy of acute promyelocytic leukaemia revisited

Since the initial description of the disease, the life-threatening coagulopathy associated with acute promyelocytic leukaemia (APL) has been the defining clinical characteristic. Historically, this uncommon subtype of acute myeloid leukaemia has been associated with a high mortality rate during induction therapy, most frequently attributable to haemorrhage. Since the introduction of all-trans retinoic acid (ATRA) into the therapy of all patients with APL, disease-free survival and overall survival have improved dramatically, such that the disease is now highly curable. However, induction mortality remains a major problem and haemorrhage still accounts for the majority of such early deaths. Pathogenesis of the coagulopathy is complex and includes disseminated intravascular coagulation (DIC), fibrinolysis and proteolysis. As a result, while the predominant clinical manifestation of the coagulopathy is haemorrhage, thromboembolic events may occur both at presentation and during therapy. A major recent finding is the high expression of annexin II in the leukaemic cells from patients with APL. Annexin II is a protein with high affinity for plasminogen and tissue-type plasminogen activator (tPA), and also acts as a cofactor for plasminogen activation by tPA. As a result, both plasminogen and tPA are increased on the cell surface of the leukaemic cell, increasing plasmin activity. Annexin II is expressed in high amounts in cerebral microvascular endothelial cells, perhaps accounting for the relatively high incidence of intracranial haemorrhage in APL compared with other sites. Microparticles are cell-derived membrane fragments originating from normal cells or released from malignant cells involved in activating coagulation. Recent studies have found that microparticles containing tissue factor, tPA, plasminogen activator inhibitor-1 and annexin II have been found in the plasma of APL patients, suggesting a role in pathogenesis of the coagulopathy. Treatment of the coagulopathy remains primarily supportive. Aggressive transfusions of platelets and cryoprecipitate appear to be important. There is no clear role for the routine use of heparin or antifibrinolytic therapy. The most important factor may be the early introduction of ATRA at the first suspicion of a diagnosis of APL, before it is confirmed genetically.

A comprehensive review of acute promyelocytic leukemia in children

The outcome of patients with acute promyelocytic leukemia (APL) has substantially improved since the successful introduction of tretinoin, and nowadays combining tretinoin with chemotherapy is potentially curative for at least 70-75% of patients with newly diagnosed APL. In most pediatric series, APL represents < or = 10% of childhood acute myelogenous leukemia. APL in children is more common in girls and in obese children. It is characterized by a higher incidence of hyperleukocytosis, an increased incidence of microgranular morphology and by more frequent occurrence of the PML/RARalpha isoforms bcr 2 and bcr 3 compared to adults. Tretinoin-based therapy is curative for the majority of children with APL. Recent data indicate that > or = 2 negative RT-PCR assays for PML/RARalpha on bone marrow performed at least 1 month apart after completing therapy are strongly associated with long-term remissions, while conversion to PCR positivity for PML/RARalpha during remission is highly predictive of impending relapse. Data from recent studies in adults and limited data from children show that arsenic trioxide is the single most effective agent in APL and deserves immediate study in newly diagnosed children in an effort to further improve prognosis and to limit exposure to conventional cytotoxic chemotherapy.

Down syndrome with microgranular variant of acute promyelocytic leukemia in a child: a case report

BACKGROUND

Acute promyelocytic leukemia (APL) accounts for less than 10% of pediatric AML. Cases of APL in Down syndrome (DS) have been described in the literature rarely and it is rarer still to find the microgranular variant (M3v) of APL in trisomy 21 patients.

CASE PRESENTATION

We present a case of a five-year-old female with Down syndrome diagnosed with acute promyelocytic leukemia (APL). She came to our hospital with bleeding manifestations. Blood and bone marrow examination revealed promyelocytes showing a few fine granules and occasional Auer rods. Based on this morphology and cytochemistry, a diagnosis of APL microgranular variant (M3v) was made.

CONCLUSION

This case report emphasizes the importance of a high index of suspicion in the diagnosis of acute promyelocytic leukemia microgranular variant in Down syndrome.

Microgranular and t(11;17)/PLZF-RARalpha variants of acute promyelocytic leukemia also present the flow cytometric pattern of CD13, CD34, and CD15 expression characteristic of PML-RARalpha gene rearrangement

Acute promyelocytic leukemia (APL) is a subtype acute myeloid leukemia in which leukemic promyelocytes predominate in the bone marrow (BM). Rapid diagnosis is critical for treatment decision since all-trans-retinoic acid must be administrated promptly. The microgranular variant may be of difficult diagnosis, as it may be confused with other diseases on morphological grounds. The purpose of this study was to determine if the microgranular variant has the same antigenic profile as the classical hypergranular type. The immunophenotype of leukemic cells from the bone marrow of 50 patients, with the PML-RARalpha gene rearrangement confirmed by RT-PCR, was determined by flow cytometry using a large panel of 22 monoclonal antibodies and a polyclonal anti-TdT antibody. Thirty-four cases were classified as classical APL and 16 as microgranular APL. The immunophenotypic profile of the two subtypes was indistinguishable concerning the presence or absence of these antigens, including the absence of reactivity for the HLA-DR antigen. The simultaneous immunophenotypic combination of a unique major cell population, heterogeneous intensity of expression of CD13, and the typical pattern of CD15/CD34 expression were similarly present in the hypergranular and microgranular subtypes. Homogeneous expression of CD33 was observed in 76% of the classical APL cases and in 100% of the microgranular cases. Additionally, we have studied two cases of PLZF-RARalpha APL that also displayed the same immunophenotype described for classical APL. Thus, the immunophenotypic profile highly characteristic of the PML-RARalpha gene rearrangement was also observed in microgranular and PLZF-RARalpha variants of APL.

Morphological and cytochemical characteristics of leukaemic promyelocytes

Evaluation of cell morphology is usually sufficient to diagnose acute promyelocytic leukaemia (APL). In this chapter we discuss the features of classical hypergranular APL, the APL variant, hyperbasophilic promyelocytic leukaemia, APL with basophil-like granules, acute eosinophilic leukaemia with PML/RARalpha positivity and the morphology of APL cells lacking t(15;17). In addition to morphological examination, cytochemical investigations (peroxidase chloroacetate-esterase, etc.) may help further in defining the cytology of leukaemic cells in APL.

PML-RAR induces promyelocytic leukemias with high efficiency following retroviral gene transfer into purified murine hematopoietic progenitors

Acute promyelocytic leukemia (APL) is associated with chromosomal translocations resulting in fusion proteins of the retinoic acid receptor (RAR). Here, we report a novel murine model system for APL, based on the transduction of purified murine hematopoietic progenitors (lin(-)) using high-titer retroviral vectors encoding promyelocytic leukemia-RAR (PML-RAR), and the green fluorescent protein (GFP) as a marker. PML-RAR-expressing lin(-) cells were impaired in their ability to undergo terminal myeloid differentiation and showed increased proliferative potential in vitro. Inoculation of transduced lin(-) cells into syngeneic, irradiated mice resulted in the development of retinoic acid-sensitive promyelocytic leukemias at high frequency (> 80%) and short latency (approximately 4 months). Morphologic and immunophenotypic analysis revealed no gross abnormalities of the preleukemic bone marrows. However, hematopoietic progenitors from PML-RAR preleukemic mice showed a severe impairment in their ability to undergo myeloid differentiation in vitro. This result, together with the monoclonality or oligoclonality of the leukemic blasts, supports a "multiple-hit" model, where the fusion protein causes a "preleukemic" phase, and leukemia occurs after additional genetic lesions. This model system faithfully reproduces the main characteristics of human APL and represents a versatile tool for the in vitro and in vivo study of mechanisms of leukemogenesis and the design of protocols for differentiation treatment.

Leukemias resembling acute promyelocytic leukemia, microgranular variant

Acute promyelocytic leukemia (APL) should be distinguished from other subtypes of acute myeloid leukemia (AML) because of the increased risk of disseminated intravascular coagulation (DIC) and its response to arsenic compounds and retinoids. Some cases of AML seem morphologically similar to the microgranular variant of APL (French-American-British [FAB] AML-M3v) but lack the t(15;17). We evaluated 8 cases of APL-like leukemias for subtle morphologic, cytochemical, immunophenotypic, and cytogenetic differences compared with 5 cases of promyelocytic leukemia/retinoic receptor alpha (PML/RARalpha)-positive APL (FAB AML-M3v). We also evaluated both groups for the presence of DIC. No differences among the groups were noted in blast size, chromatin pattern, nuclear morphologic features, intensity of myeloperoxidase staining, or presence of Auer rods. Immunophenotypes were similar; both types of cases lacked CD34 and HLA-DR and were CD13+ and CD33+. Two cases of APL-like leukemias also were CD56+. DIC was present in 2 patients with M3v. Our study shows that there are no definitive morphologic, cytochemical, or immunophenotypic findings that can distinguish these cases from PML/RARalpha-positive APL.

Biological features of primary APL blasts: their relevance to the understanding of granulopoiesis, leukemogenesis and patient management

In recent years, discovery of the in vitro and in vivo differentiation of APL blasts by all-trans retinoic acid (ATRA) has modified the therapeutic approach of APL and lead to important advances in understanding the biology of APL. Since it became apparent that differentiation therapy of APL with ATRA was indeed a true model of targetted therapy, evidencing the molecular targets of retinoic acid efficacy became crucial. These molecular targets are closely related to the biological features of APL cells, some of which are well-known and have contributed to the morphological and cytogenetic definition of the leukemia, others have just been defined or re-discovered in the light of a better understanding of molecular controls of cell growth and differentiation. The aims of characterizing the biological features of APL cells should allow a better management of APL therapy and the identification of potential markers for differentiation therapies in other leukemias or solid tumors.

A variant form of acute promyelocytic leukemia with marked myelofibrosis

We describe a variant form, French-American-British (FAB) M3v, of acute promyelocytic leukemia (APL; FAB M3) with atypical morphocytochemical features, immature antigens (CD34 and HLA-DR) and marked myelofibrosis (MF). Usual APL cells do not express CD34 or HLA-DR antigens. MF may be more frequently observed in patients with M3v expressing CD34 and HLA-DR antigens than in patients with M3 lacking these antigens. Despite marked MF, recovery from the hypoplastic phase in the case we described was not delayed after remission induction chemotherapy consisting of enocitabine, 200 mg/mi2 intravenously; 6-mercaptopurine, 70 mg/m2 orally for 10 days; daunorubicin 40 mg/m2 intravenously for 4 days; and all-trans retinoic acid 45 mg/M2 orally between days 20 and 33. The promyelocytic leukemia-retinoic-acid receptor (PML-RAR) alpha fusion transcript, according to reverse transcriptase-polymerase chain reaction (RT-PCR), became negative in the bone marrow after the first course of consolidation chemotherapy. Autologous peripheral blood stem cell transplantation (autoPBSCT) was carried out after 3 courses of consolidation chemotherapy. There were no specific complications based on MF throughout the clinical course, including engraftment in autoPBSCT. The patient has been without MF and in molecular remission, defined as disappearance of the PML-RAR alpha fusion transcript according to RT-PCR, for 21 months. Longer follow-up will clarify the effects of autoPBSCT on prognosis in APL with MF.

CD34-positive acute promyelocytic leukemia is associated with leukocytosis, microgranular/hypogranular morphology, expression of CD2 and bcr3 isoform

Acute promyelocytic leukemia (APL) has a favorable prognosis. Current therapy includes chemotherapy used in combination with all-trans-retinoic acid (ATRA). Although the differentiating effects of ATRA on promyelocytes have been well established, in vitro studies have shown that less-differentiated APL blasts (CD34(+)) demonstrate a variable responsiveness to ATRA. To assess the clinical relevance of this finding, we analyzed a cohort of 38 patients with t(15;17) and/or PML-RARalpha APL to determine the incidence and laboratory features of CD34(+) APL. Thirty-two percent (12/38) of cases were CD34(+). There was a difference in WBC at presentation between CD34(+) and CD34(-) cases (34.6 +/- 9.2, mean +/- standard error vs. 5.4 +/- 2.0, P = 0.009). Patients with CD34(+) APL demonstrated a micro/hypogranular phenotype (75%) (P = 0.001), co-expression of CD2(+) (83%) (P = 0.001), and the bcr3 isoform (100%) (P = 0.017). In contrast, CD34(-) cases demonstrated hypergranular morphology (65%), CD2(+) (15%), and the bcr1 isoform (50%). A high presenting WBC count (\G10 x 10(9)/L) was associated with an inferior overall survival (Log rank = 0.0047). Patients with CD34(+) APL demonstrated an incidence of early mortality of 50%. Despite a marked correlation between CD34 positivity and increased WBC count, overall survival of CD34(+) and CD34(-) cases did not differ significantly in our small cohort. Immunophenotypic analysis for CD34 expression should be included in future large APL trials to determine if detection of CD34(+) blasts represents an independent adverse prognostic factor.

Realistic pathologic classification of acute myeloid leukemias

Most classification systems of acute myeloid leukemia (AML) rely largely on the criteria proposed by the French-American-British (FAB) Cooperative Group. The recently proposed World Health Organization (WHO) classification of neoplastic diseases of the hematopoietic and lymphoid tissues includes a classification of AMLs. The proposed WHO classification of AMLs includes traditional FAB-type categories of disease, as well as additional disease types that correlate with specific cytogenetic findings and AML associated with myelodysplasia. This system includes a large number of disease categories, many of which are of unknown clinical significance, and there seems to be substantial overlap between disease groups in the WHO proposal. Some disease types in the WHO proposal cannot be diagnosed without detailed clinical information, or they are diagnosed only by the cytogenetic findings. In this report, a realistic pathologic classification for AML is proposed that includes disease types that correlate with specific cytogenetic translocations and can be recognized reliably by morphologic evaluation and immunophenotyping and that incorporates the importance of associated myelodysplastic changes. This system would be supported by cytogenetic or molecular genetic studies and could be expanded as new recognizable clinicopathologic entities are described.

Acute progranulocytic leukemia

Acute progranulocytic leukemia (APL) is characterized by unique biologic and clinical features. Understanding of these unique features has resulted in dramatic improvements in therapy for patients with APL. Current therapy with all-trans-retinoic acid (ATRA) plus an anthracycline with or without cytosine-arabinoside has yielded complete response rates of 85% or greater and long-term disease-free survival rates of 70% or greater. Arsenic trioxide has also surfaced as an effective induction therapy for relapsed APL. Further progress in the care of patients with APL awaits better definition of optimal schedules for ATRA plus chemotherapy, the role of arsenic trioxide, the use of current molecular monitoring for minimal residual disease, optimal therapy for minimal residual disease, and improved methods to address complications of APL including early hemorrhagic deaths and ATRA toxicities.

Rapid diagnosis of acute promyelocytic leukemia by analyzing the immunocytochemical pattern of the PML protein with the monoclonal antibody PG-M3

The fusion protein, promyelocytic leukemia-retinoic acid receptor (PML-RAR)alpha, generated by the t(15;17) translocation has an abnormal cellular distribution with colocalization of RARalpha and PML proteins. We analyzed the immunostaining pattern of PML protein using the PG-M3 monoclonal antibody directed against the amino terminal portion of PML (retained in wild-type PML and PML-RARalpha fusion protein) in the diagnosis of acute promyelocytic leukemia (APL). In addition, we compared this test with other methods for detecting the PML-RARalpha fusion gene. A normal immunostaining pattern was observed in nonmyeloid disorders and in 78 of 111 acute myeloid leukemias (AMLs). A microgranular pattern was observed in 25 AMLs, all corresponding to APL. These results were concordant with the reverse transcriptase-polymerase chain reaction results for PML-RARalpha fusion gene. Only 1 case positive for the PML-RARalpha transcript showed a normal protein pattern by immunocytochemistry. PML immunostaining was helpful to rapidly differentiate 7 cases with borderline characteristics and to obtain the diagnosis in 2 cases with scarce material. The effectiveness and low cost of this technique support its routine use as a first-line procedure in the differential diagnosis of AML.

Tetraploid acute promyelocytic leukemia with large bizarre blast cell morphology

We describe a case of atypical acute promyelocytic leukemia (APL) with a tetraploid clone and multiple karyotypic abnormalities in addition to the translocation (15;17)(q22;q21). Microscopically, the leukemic cells were highly heterogeneous in morphology and granularity, being bizarre and large in size compared with classical APL blasts. The patient responded to treatment with chemotherapy and all-trans-retinoic acid, at diagnosis and at relapse 10 months later. He is currently in clinical and molecular remission, 3 years after initial diagnosis. Tetraploidy in association with large and bizarre blasts has not been previously reported in APL. Although tetraploidy and complex karyotypic aberrations confer a poor prognosis in other types of acute myeloid leukemia, in the presence of t(15;17) they did not appear to affect the prognosis, inasmuch as the clinical features and treatment outcome in our case followed those of APL in general.

Development of acute promyelocytic leukemia with isochromosome 17q after BCR/ABL positive chronic myeloid leukemia

We describe a pediatric case of acute promyelocytic leukemia with an i(17q) after treatment of BCR/ABL positive chronic myeloid leukemia (CML) for 3.5 years. The patient was treated with Busulphan, alpha-2a interferon, hydroxyurea, and cytosine arabinoside at various times in the course of the chronic phase of CML, because he had no HLA-identical donor for bone marrow transplantation. Hematologic remission was achieved for a short time, but cytogenetic remission was never possible. When promyelocytic blast crisis was diagnosed according to the French-American-British classification, cytogenetic studies revealed an i(17q) as a new feature in our patient. The promyelocytic transformation was associated with the appearance of an i(17q) preceding CML are discussed in the light of recent literature.