Acute promyelocytic leukaemia with t(11;17)(q23;q12-21) and a good initial response to prolonged ATRA and combination chemotherapy

Spinal myeloid sarcoma presenting as initial symptom in acute promyelocytic leukemia with a rare cryptic PLZF::RARα fusion gene: a case report and literature review

Background

Acute promyelocytic leukemia (APL) is rarely caused by the PLZF::RARα fusion gene. While APL patients with PLZF::RARα fusion commonly exhibit diverse hematologic symptoms, the presentation of myeloid sarcoma (MS) as an initial manifestation is infrequent.

Case presentation

A 61-year-old patient was referred to our hospital with 6-month history of low back pain and difficulty walking. Before this admission, spine magnetic resonance imaging (MRI) conducted at another hospital revealed multiple abnormal signals in the left iliac bone and vertebral bodies spanning the thoracic (T11-T12), lumbar (L1-L4), and sacral (S1/S3) regions. This led to a provisional diagnosis of bone tumors with an unknown cause. On admission, complete blood count (CBC) test and peripheral blood smear revealed a slightly increased counts of monocytes. Immunohistochemical staining of both spinal and bone marrow (BM) biopsy revealed positive expression for CD117, myeloperoxidase (MPO), and lysozyme. BM aspirate showed a significant elevation in the percentage of promyelocytes (21%), which were morphologically characterized by round nuclei and hypergranular cytoplasm. Multiparameter flow cytometry of BM aspirate revealed that blasts were positive for CD13, CD33, CD117, and MPO. Through the integrated application of chromosome analysis, fluorescence in situ hybridization (FISH), reverse transcriptase polymerase chain reaction (RT-PCR), and Sanger sequencing, it was determined that the patient possessed a normal karyotype and a rare cryptic PLZF::RARα fusion gene, confirming the diagnosis of APL.

Conclusion

In the present study, we report the clinical features and outcome of a rare APL patient characterized by a cryptic PLZF::RARα fusion and spinal myeloid sarcoma (MS) as the initial presenting symptom. Our study not only offers valuable insights into the heterogeneity of APL clinical manifestations but also emphasizes the crucial need to promptly consider the potential link between APL and MS for ensuring a timely diagnosis and personalized treatments.

PLZF-RARα, NPM1-RARα, and Other Acute Promyelocytic Leukemia Variants: The PETHEMA Registry Experience and Systematic Literature Review

It has been suggested that 1–2% of acute promyelocytic leukemia (APL) patients present variant rearrangements of retinoic acid receptor alpha (RARα) fusion gene, with the promyelocytic leukaemia zinc finger (PLZF)/RAR_α being the most frequent. Resistance to all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO) has been suggested in PLZF/RAR_α and other variant APLs. Herein, we analyze the incidence, characteristics, and outcomes of variant APLs reported to the multinational PETHEMA (Programa para el Tratamiento de Hemopatias Malignas) registry, and we perform a systematic review in order to shed light on strategies to improve management of these extremely rare diseases. Of 2895 patients with genetically confirmed APL in the PETHEMA registry, 11 had variant APL (0.4%) (9 PLZF-RAR_α and 2 NPM1-RAR_α), 9 were men, with median age of 44.6 years (3 months to 76 years), median leucocytes (WBC) 16.8 × 10⁹/L, and frequent coagulopathy. Eight patients were treated with ATRA plus chemotherapy-based regimens, and 3 with chemotherapy-based. As compared to previous reports, complete remission and survival was slightly better in our cohort, with 73% complete remission (CR) and 73% survival despite a high relapse rate (43%). After analyzing our series and performing a comprehensive and critical review of the literature, strong recommendations on appropriate management of variant APL are not possible due to the low number and heterogeneity of patients reported so far.

Characterization of atypical acute promyelocytic leukaemia: Three cases report and literature review

RATIONALE

The vast majority of acute promyelocytic leukemia (APL) is characterized with a specific chromosomal translocation t (15, 17) (q22, q21), which fuses PML-RARα leading to a good response to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). However, there are few cases of atypical APL, including PLZF-RARα, F1P1L1-RARα, STAT5b-RARα, et al. Neither PLZF-RARα nor STAT5b-RARα are sensitive to ATRA and ATO, and the prognosis is poor.

PATIENT CONCERNS

Here we have 3 cases (PLZF-RARα, n = 2; STAT5b-RARα, n = 1). Case A, A 53-year-old Chinese female had suffered ecchymosis in both legs for 3 days. Case B, A 44 years old male suffered pain from lower limbs and hip. Case C, 52-year-old male patient presented with fever for 3 weeks invalid to antibiotics and gingival bleeding for 1 week.

DIAGNOSES

With RT-PCR and karyotype, Case A is diagnosed with STAT5b-RARα-positive APL.Case B, C are diagnosed with PLZF-RARα-positive APL.

INTERVENTIONS

In case A, ATO, and ATRA were used for induction treatment. In Case B, ATO, and chemotherapy with DA were given in the first induction treatment. In Case C, ATRA, and ATO were used immediately, subsequently, chemotherapy was added with DA, ATRA, and CAG combination treatment, and medium-dose cytarabine with daunorubicin were given regularly.

OUTCOMES

In Case A, the patient refused the following treatment and discharged on day 25. In Case B, the patient got the disseminated intravascular coagulation (DIC).In Case C, the patient has survived for 7 months and remains CR.

LESSONS

Both STAT5b-RARα-positive APL and PLZF-RARα-positive APL appear to be resistant to both ATRA and ATO, so combined chemotherapy and allo-HSCT should be considered. Since the prognosis and long-term outcome are poor, more clinical trials, and researches should be taken.

Molecular Profiling: A Case of ZBTB16-RARA Acute Promyelocytic Leukemia

Several variant RARA translocations have been reported in acute promyelocytic leukemia (APL) of which the t(11;17)(q23;q21), which results in a ZBTB16-RARA fusion, is the most widely identified and is largely resistant to therapy with all-trans retinoic acid (ATRA). The clinical course together with the cytogenetic and molecular characterization of a case of ATRA-unresponsive ZBTB16-RARA APL is described. Additional mutations potentially cooperating with the translocation fusion product in leukemogenesis have been hitherto unreported in ZBTB16-RARA APL and were sought by application of a next-generation sequencing approach to detect those recurrently found in myeloid malignancies. This technique identified a solitary, low level mutation in the CEBPA gene. Molecular profiling of additional mutations may provide a platform to individualise therapeutic management in patients with this rare form of APL.

Development of real-time quantitative polymerase chain reaction assays to track treatment response in retinoid resistant acute promyelocytic leukemia

Molecular detection of minimal residual disease (MRD) has become established to assess remission status and guide therapy in patients with ProMyelocytic Leukemia-RARA+ acute promyelocytic leukemia (APL). However, there are few data on tracking disease response in patients with rarer retinoid resistant subtypes of APL, characterized by PLZF-RARA and STAT5b-RARA. Despite their rarity (<1% of APL) we identified 6 cases (PLZF-RARA, n = 5; STAT5b-RARA, n = 1), established the respective breakpoint junction regions and designed reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) assays to detect leukemic transcripts. The relative level of fusion gene expression in diagnostic samples was comparable to that observed in t(15;17) - associated APL, affording assay sensitivities of ∼1 in 10(4)-10(5). Serial samples were available from two PLZF-RARA APL patients. One showed persistent polymerase chain reaction positivity, predicting subsequent relapse, and remains in CR2, ∼11 years post-autograft. The other, achieved molecular remission (CRm) with combination chemotherapy, remaining in CR1 at 6 years. The STAT5b-RARA patient failed to achieve CRm following frontline combination chemotherapy and ultimately proceeded to allogeneic transplant on the basis of a steadily rising fusion transcript level. These data highlight the potential of RT-qPCR detection of MRD to facilitate development of more individualized approaches to the management of rarer molecularly defined subsets of acute leukemia.

The PLZF gene of t (11;17)-associated APL

The PLZF gene is one of five partners fused to the retinoic acid receptor alpha in acute promyelocytic leukemia. PLZF encodes a DNA-binding transcriptional repressor and the PLZF-RARalpha fusion protein like other RARalpha fusions can inhibit the genetic program mediated by the wild tpe retinoic acid receptor. However an increasing body of literature indicates an important role for the PLZF gene in growth control and development. This information suggests that loss of PLZF function might also contribute to leukemogenesis.

Hematological and molecular remission with combination chemotherapy in a patient with PLZF-RARalpha acute promyelocytic leukemia (APML)

Patients with acute promyelocytic leukemia (APML) with the t(11;17) translocation usually respond poorly to all-trans retinoic acid (ATRA) and chemotherapy. We describe a patient with promyelocytic leukemia zinc finger/retinoic acid receptor alpha (PLZF/RARalpha) APML who was treated with combination chemotherapy after poor response to arsenic trioxide. He achieved hematological remission in 4 weeks followed by achievement of molecular remission in 8 weeks. Four cycles of consolidation chemotherapy followed by four cycles of maintenance therapy were given over a period of 9 months. At a follow-up of 32 months after achieving hematological remission, he continues to remain in hematological and molecular remission with normal blood parameters and negative reverse transcriptase polymerase chain reaction (RT-PCR) results. Combination chemotherapy can achieve sustained remission in patients with PLZF/RARalpha APML.

Molecular pathogenesis of acute promyelocytic leukaemia and APL variants

It has been 12 years since the simultaneous discovery of the unique sensitivity of acute promyelocytic leukaemia (APL) to differentiation therapy with all-trans retinoic acid (ATRA) and the discovery that the retinoic acid receptor alpha (RARalpha) gene was rearranged in APL. Nearly 98% of cases of APL are associated with t(15;17) chromosomal translocation and fusion of the PML gene to that encoding RARalpha to yield an abnormal receptor with the capability of de-regulating gene expression in the haematopoietic cell, causing differentiation block and eventually the development of leukaemia. Since this original discovery, four other translocations were described in APL. In each of these the RARalpha gene is fused to different partner genes, all yielding aberrant nuclear receptors. These fusion proteins share in common the ability to repress rather than activate retinoic acid targets, one so strongly that the result is an ATRA-resistant form of the disease. In addition each of the partner proteins is important for normal cell growth and development. In this chapter we explore the biology of the RARalpha, the fusion proteins created in APL and the normal forms of the partner proteins. Through continued study of this disease it is hoped that novel treatments, potentially more applicable to other forms of leukaemia, may arise.

Treatment of acute promyelocytic leukemia: strategy toward further increase of cure rate

Acute promyelocytic leukemia (APL) has become a curable disease by all-trans retinoic acid (ATRA)-based induction therapy followed by two or three courses of consolidation chemotherapy. Currently around 90% of newly diagnosed patients with APL achieve complete remission (CR) and over 70% of patients are curable. To further increase the CR and cure rates, detection and diagnosis of this disease at its early stage is very important, hopefully before the appearance of APL-associated coagulopathy. In induction therapy, concomitant chemotherapy is indispensable, except for patients with low initial leukocyte counts. Prophylactic use of intrathecal methotrexate and cytarabine should be done, particularly for patients with hyperleukocytosis. If patients relapse hematologically or even molecularly, arsenic trioxide will be the treatment of choice under careful electrocardiogram monitoring. Am80, liposomal ATRA, gemtuzumab ozogamicin or ATRA in combination with cytotoxic drugs may be used at this stage or later. Allogeneic SCT will be the treatment of choice after patients of age <50 years have relapsed, provided that they have HLA-identical family donors or DNA-identical unrelated donors.

The molecular pathogenesis of acute promyelocytic leukaemia: implications for the clinical management of the disease

Acute promyelocytic leukaemia (APL) is characterised by chromosomal rearrangements of 17q21, leading to fusion of the gene encoding retinoic acid receptor alpha (RARalpha) to a number of alternative partner genes (X), the most frequent of which are PML (>95%), PLZF (0.8%) and NPM (0.5%). Over the last few years, it has been established that the X-RARalpha fusion proteins play a key role in the pathogenesis of APL through recruitment of co-repressors and the histone deacetylase (HDAC)-complex to repress genes implicated in myeloid differentiation. Paradoxically, the X-RARalpha fusion protein has the potential to mediate myeloid differentiation at pharmacological doses of its ligand (all trans-retinoic acid (ATRA)), which is dependent on the dissociation of the HDAC/co-repressor complex. Arsenic compounds have also been shown to be promising therapeutic agents, leading to differentiation and apoptosis of APL blasts. It is now apparent that the nature of the RARalpha-fusion partner is a critical determinant of response to ATRA and arsenic, underlining the importance of cytogenetic and molecular characterisation of patients with suspected APL to determine the most appropriate treatment approach. Standard protocols involving ATRA combined with anthracycline-based chemotherapy, lead to cure of approximately 70% patients with PML-RARalpha-associated APL. Patients at high risk of relapse can be identified by minimal residual disease monitoring. The challenge for future studies is to improve complete remission rates through reduction of induction deaths, particularly due to haemorrhage, identification of patients at high risk of relapse who would benefit from additional therapy, and identification of a favourable-risk group, for which treatment intensity could be reduced, thereby reducing risks of treatment toxicity and development of secondary leukaemia/myelodysplasia. With the advent of ATRA and arsenic, APL has already provided the first example of successful molecularly targeted therapy; it is hoped that with further understanding of the pathogenesis of the disease, the next decade will yield further improvements in the outlook for these patients.

Translocations of the RARalpha gene in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) has been recognized as a distinct clinical entity for over 40 years. Although relatively rare among hematopoietic malignancies (approximately 10% of AML cases), this disease has attracted a particularly good share of attention by becoming the first human cancer in which all-trans-retinoic acid (ATRA), a physiologically active derivative of vitamin A, was able to induce complete remission (CR). ATRA induced remission is not associated with rapid cell death, as in the case of conventional chemotherapy, but with a restoration of the 'normal' granulocytic differentiation pathway. With this remarkable medical success story APL has overnight become a paradigm for the differentiation therapy of cancer. A few years later, excitement with APL was further enhanced by the discovery that a cytogenetic marker for this disease, the t(15:17) reciprocal chromosomal translocation, involves a fusion between the retinoic acid receptor alpha (RARalpha) gene and a previously unknown locus named promyelocytic leukemia (PML). Consequence of this gene rearrangement is expression of the PML-RARalpha chimeric oncoprotein, which is responsible for the cellular transformation as well as ATRA response that is observed in APL. Since this initial discovery, a number of different translocation partner genes of RARalpha have been reported in rarer cases of APL, strongly suggesting that disruption of RARalpha underlies its pathogenesis. This article reviews various rearrangements of the RARalpha gene that have so far been described in literature, functions of the proteins encoded by the different RARalpha partner loci, and implications that these may have for the molecular pathogenesis of APL.

Estrogen-dependent E2a/Pbx1 myeloid cell lines exhibit conditional differentiation that can be arrested by other leukemic oncoproteins

The molecular pathways of normal myeloid differentiation, as well as the mechanisms by which oncogenes disrupt this process, remain poorly understood. A major limitation in approaching this problem has been the lack of suitable cell lines that exhibit normal, terminal, and synchronous differentiation in the absence of endogenous oncoproteins and in response to physiologic cytokines, and whose differentiation can be arrested by ectopically expressed human oncoproteins. This report describes clonal, granulocyte-macrophage colony-stimulating factor-dependent myeloid cell lines that exhibit these properties. The cell lines were established by conditional immortalization of primary murine marrow progenitors with an estrogen-regulated E2a/Pbx1-estrogen receptor fusion protein. Clones were identified that proliferated as immortalized blasts in the presence of estrogen, and that exhibited granulocytic, monocytic, or bipotential (granulocytic and monocytic) differentiation on estrogen withdrawal. Differentiation was normal and terminal as evidenced by morphology, cell surface markers, gene expression, and functional assays. The differentiation of the cells could be arrested by heterologous oncoproteins including AML1/ETO, PML/RARalpha, PLZF/RARalpha, Nup98/HoxA9, and other Hox proteins. Furthermore, the study examined the effects of cooperating oncoproteins such as Ras or Bcr/Abl, which allowed for both factor-independent proliferation and differentiation, or Bcl-2, which permitted factor-independent survival but not proliferation. These myeloid cell lines provide tools for examining the biochemical and genetic pathways that accompany normal differentiation as well as a system in which to dissect how other leukemic oncoproteins interfere with these pathways.

Histone deacetylase inhibitor but not arsenic trioxide differentiates acute promyelocytic leukaemia cells with t(11;17) in combination with all-trans retinoic acid

Acute promyelocytic leukaemia (APL) with t(11;17)/PLZF-RARalpha responds poorly to all-trans retinoic acid (ATRA) and arsenic trioxide (As2O3), in contrast to APL with t(15;17)/PML-RARalpha. Molecular studies have shown that histone deacetylase (HDAC) recruited by PLZF-RARalpha is associated with the ATRA resistance. Here, we analysed in vitro the differentiation of APL cells with t(11;17) using ATRA, As203, granulocyte colony-stimulating factor (G-CSF), HDAC inhibitor trichostatin A (TSA), or combinations of these. Although 1 microM ATRA, which stimulated the differentiation of APL cells with t(15;17), was insufficient to induce differentiation, 3 microM ATRA induced terminal differentiation into granulocytes. As203 alone or in combination with ATRA induced neither differentiation nor apoptosis. However, the combination of TSA and 1 microM ATRA had a potent differentiating effect, although TSA alone had little effect. The combination of 1 microM ATRA and G-CSF did not induce differentiation. These results indicate that APL cells with t(11;17) need a higher concentration of ATRA than those with t(15;17) to differentiate and suggest that HDAC inhibitor is a promising differentiation enhancer in APL with t(11;17).

Complete Remission of t(11;17) Positive Acute Promyelocytic Leukemia Induced by All-trans Retinoic Acid and Granulocyte Colony-Stimulating Factor

The combined use of retinoic acid and chemotherapy has led to an important improvement of cure rates in acute promyelocytic leukemia. Retinoic acid forces terminal maturation of the malignant cells and this application represents the first generally accepted differentiation-based therapy in leukemia. Unfortunately, similar approaches have failed in other types of hematological malignancies suggesting that the applicability is limited to this specific subgroup of patients. This has been endorsed by the notorious lack of response in acute promyelocytic leukemia bearing the variant t(11;17) translocation. Based on the reported synergistic effects of retinoic acid and the hematopoietic growth factor granulocyte colony-stimulating factor (G-CSF), we studied maturation of t(11;17) positive leukemia cells using several combinations of retinoic acid and growth factors. In cultures with retinoic acid or G-CSF the leukemic cells did not differentiate into mature granulocytes, but striking granulocytic differentiation occurred with the combination of both agents. At relapse, the patient was treated with retinoic acid and G-CSF before reinduction chemotherapy. With retinoic acid and G-CSF treatment alone, complete granulocytic maturation of the leukemic cells occurred in vivo, followed by a complete cytogenetical and hematological remission. Bone marrow and blood became negative in fluorescense in situ hybridization analysis and semi-quantitative polymerase chain reaction showed a profound reduction of promyelocytic leukemia zinc finger–retinoic acid receptor- fusion transcripts. This shows that t(11;17) positive leukemia cells are not intrinsically resistant to retinoic acid, provided that the proper costimulus is administered. These observations may encourage the investigation of combinations of all-trans retinoic acid and hematopoietic growth factors in other types of leukemia.

Biology and treatment of acute progranulocytic leukemia

Acute progranulocytic leukemia (APL) is one of the most curable of all human cancers. Combination treatment with retinoic acid (RA) and anthracycline-based chemotherapy is safe and effective for the vast majority of patients, and several novel treatment approaches are under investigation for high-risk or relapsed patients. The APL-specific oncogenes PML-RAR alpha and PLZF-RAR alpha both bind nuclear corepressors and recruit histone deacetylase activity to promoters of RA target genes. The differential sensitivity of binding of these oncogenes to nuclear corepressors in the presence of RA appears to explain the resistance of PLZF-RAR alpha-related APL to RA and at the same time explains the effectiveness of RA in PML-RAR alpha-positive APL. Transcriptional repression of RA target genes, mediated by histone deacetylase activity, may thus be a key pathogenetic event in APL. Cure of the minority of resistant patients requires further refinement of current treatment approaches and appropriately timed incorporation of novel therapies, such as arsenic trioxide or histone deacetylase inhibitors.

Presenting White Blood Cell Count and Kinetics of Molecular Remission Predict Prognosis in Acute Promyelocytic Leukemia Treated With All-Trans Retinoic Acid: Result of the Randomized MRC Trial

All-trans retinoic acid (ATRA) is an essential component of the treatment of acute promyelocytic leukemia (APL), but the optimal timing and duration remain to be determined. Molecular characterization of this disease can refine the diagnosis and could be potentially useful in monitoring response to treatment. Patients defined morphologically to have APL were randomized to receive a 5-day course of ATRA before commencing chemotherapy or to receive daily ATRA commencing with chemotherapy and continuing until complete remission (CR). The chemotherapy was that used in current MRC Leukaemia Trials. Outcome comparisons were by intention to treat with additional analysis for relevant risk factors. Patients were characterized by molecular techniques for the fusion products of the t(15;17) and monitored by reverse transcriptase-polymerase chain reaction (RT-PCR) during and after treatment. Two hundred thirty-nine patients were randomized. Treatment with extended ATRA resulted in a superior remission rate (87% v 70%, P < .001), due to fewer early and induction deaths (12% v 23%, P = .02), and less resistant disease (2% v 7%, P = .03), which was associated with a significantly more rapid recovery of neutrophils and platelets. Extended ATRA reduced relapse risk (20%v 36% at 4 years, P = .04) and resulted in superior survival (71% v 52% at 4 years, P = .005). Presenting white blood cell count (WBC) was a key determinant of outcome. The 70% of patients who presented with a WBC less than 10 × 109/L had a better CR (85% v62%, P = .0001) and reduced relapse risk (22% v42%, P = .002) and superior survival (69%v 43%, P < .0001). Within the low count group, extended ATRA resulted in a better CR (94% v 76%, P= .001), reduced relapse risk (13% v 35%, P = .04), and improved survival (80% v 57%, P = .0009). There was no evidence of benefit in patients presenting with a higher WBC (>10 × 109/L). Molecular monitoring after the third chemotherapy course had a correlation with risk of relapse. The relapse risk was 57% if the RT-PCR was positive versus 27% if the RT-PCR was negative (P = .006). APL patients who present with a low WBC derive substantial benefit from combining ATRA with induction chemotherapy until remission is achieved, whereas patients with a higher WBC did not benefit. Molecular characterization of disease can improve diagnostic precision and a positive RT-PCR after consolidation identifies patients at a higher risk of relapse.

Presenting White Blood Cell Count and Kinetics of Molecular Remission Predict Prognosis in Acute Promyelocytic Leukemia Treated With All-Trans Retinoic Acid: Result of the Randomized MRC Trial

All-trans retinoic acid (ATRA) is an essential component of the treatment of acute promyelocytic leukemia (APL), but the optimal timing and duration remain to be determined. Molecular characterization of this disease can refine the diagnosis and could be potentially useful in monitoring response to treatment. Patients defined morphologically to have APL were randomized to receive a 5-day course of ATRA before commencing chemotherapy or to receive daily ATRA commencing with chemotherapy and continuing until complete remission (CR). The chemotherapy was that used in current MRC Leukaemia Trials. Outcome comparisons were by intention to treat with additional analysis for relevant risk factors. Patients were characterized by molecular techniques for the fusion products of the t(15;17) and monitored by reverse transcriptase-polymerase chain reaction (RT-PCR) during and after treatment. Two hundred thirty-nine patients were randomized. Treatment with extended ATRA resulted in a superior remission rate (87% v 70%, P &lt; .001), due to fewer early and induction deaths (12% v 23%, P = .02), and less resistant disease (2% v 7%, P = .03), which was associated with a significantly more rapid recovery of neutrophils and platelets. Extended ATRA reduced relapse risk (20%v 36% at 4 years, P = .04) and resulted in superior survival (71% v 52% at 4 years, P = .005). Presenting white blood cell count (WBC) was a key determinant of outcome. The 70% of patients who presented with a WBC less than 10 × 109/L had a better CR (85% v62%, P = .0001) and reduced relapse risk (22% v42%, P = .002) and superior survival (69%v 43%, P &lt; .0001). Within the low count group, extended ATRA resulted in a better CR (94% v 76%, P= .001), reduced relapse risk (13% v 35%, P = .04), and improved survival (80% v 57%, P = .0009). There was no evidence of benefit in patients presenting with a higher WBC (&gt;10 × 109/L). Molecular monitoring after the third chemotherapy course had a correlation with risk of relapse. The relapse risk was 57% if the RT-PCR was positive versus 27% if the RT-PCR was negative (P = .006). APL patients who present with a low WBC derive substantial benefit from combining ATRA with induction chemotherapy until remission is achieved, whereas patients with a higher WBC did not benefit. Molecular characterization of disease can improve diagnostic precision and a positive RT-PCR after consolidation identifies patients at a higher risk of relapse.

The biology and treatment of acute progranulocytic leukemia

Acute progranulocytic leukemia (APL) is one of the most curable of all human cancers. Combination treatment with retinoic acid (RA) and anthracycline-based chemotherapy is safe and effective for the vast majority of patients, and several novel treatment approaches are under investigation for high-risk or relapsed patients. The APL-specific oncogenes PML-RAR alpha and PLZF-RAR alpha both bind nuclear corepressors and recruit histone deacetylase activity to promoters of RA target genes. The differential sensitivity of binding of these oncogenes to nuclear corepressors in the presence of RA appears to explain the resistance of PLZF-RAR alpha-related APL to RA and at the same time explains the effectiveness of RA in PML-RAR alpha-positive APL. Transcriptional repression of RA target genes, mediated by histone deacetylase activity, may thus be a key pathogenetic event in APL. Cure of the minority of resistant patients requires further refinement of current treatment approaches and appropriately timed incorporation of novel therapies, such as arsenic trioxide or histone deacetylase inhibitors.