STAT5b-RARa-positive acute myeloid leukemia: Diagnostic and therapeutic challenges of a rare AML subtype

Treatment of a STAT5b::RARα positive case of APL in a patient not eligible for intensive chemotherapy

Acute promyelocytic leukaemia (APL) with a STAT5b::RARα gene fusion is an extremely rare subtype of APL characterised by resistance to conventional therapies and extremely poor prognosis. This case highlights that whilst APL with variant RARα translocations are rare, they do pose significant challenges both diagnostically and in their clinical management. This case, in the first instance, demonstrates the importance of using a combination of molecular techniques including next generation sequencing (NGS) for diagnosis particularly in morphological and immunophenotypic typical APL which appears negative by confirmatory testing. Secondly, our patient represents, to the best of our knowledge, the first documented example of this rare disease that has been managed with, and shown sensitivity to low-dose cytarabine (LDAC) in combination with venetoclax (Ven). This case demonstrates that although treatment options are extremely limited for patients not eligible for intensive chemotherapy non-intensive options do show increasing promise.

Function of PML-RARA in Acute Promyelocytic Leukemia

The transformation of acute promyelocytic leukemia (APL) from the most fatal to the most curable subtype of acute myeloid leukemia (AML), with long-term survival exceeding 90%, has represented one of the most exciting successes in hematology and in oncology. APL is a paradigm for oncoprotein-targeted cure.APL is caused by a 15/17 chromosomal translocation which generates the PML-RARA fusion protein and can be cured by the chemotherapy-free approach based on the combination of two therapies targeting PML-RARA: retinoic acid (RA) and arsenic. PML-RARA is the key driver of APL and acts by deregulating transcriptional control, particularly RAR targets involved in self-renewal or myeloid differentiation, also disrupting PML nuclear bodies. PML-RARA mainly acts as a modulator of the expression of specific target genes: genes whose regulatory elements recruit PML-RARA are not uniformly repressed but also may be upregulated or remain unchanged. RA and arsenic trioxide directly target PML-RARA-mediated transcriptional deregulation and protein stability, removing the differentiation block at promyelocytic stage and inducing clinical remission of APL patients.

Current views on the genetic landscape and management of variant acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by the accumulation of promyelocytes in bone marrow. More than 95% of patients with this disease belong to typical APL, which express PML-RARA and are sensitive to differentiation induction therapy containing all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), and they exhibit an excellent clinical outcome. Compared to typical APL, variant APL showed quite different aspects, and how to recognize, diagnose, and treat variant APL remained still challenged at present. Herein, we drew the genetic landscape of variant APL according to recent progresses, then discussed how they contributed to generate APL, and further shared our clinical experiences about variant APL treatment. In practice, when APL phenotype was exhibited but PML-RARA and t(15;17) were negative, variant APL needed to be considered, and fusion gene screen as well as RNA-sequencing should be displayed for making the diagnosis as soon as possible. Strikingly, we found that besides of RARA rearrangements, RARB or RARG rearrangements also generated the phenotype of APL. In addition, some MLL rearrangements, NPM1 rearrangements or others could also drove variant APL in absence of RARA/RARB/RARG rearrangements. These results indicated that one great heterogeneity existed in the genetics of variant APL. Among them, only NPM1-RARA, NUMA-RARA, FIP1L1-RARA, IRF2BP2-RARA, and TFG-RARA have been demonstrated to be sensitive to ATRA, so combined chemotherapy rather than differentiation induction therapy was the standard care for variant APL and these patients would benefit from the quick switch between them. If ATRA-sensitive RARA rearrangement was identified, ATRA could be added back for re-induction of differentiation. Through this review, we hoped to provide one integrated view on the genetic landscape of variant APL and helped to remove the barriers for managing this type of disease.

Acute Promyelocytic Leukemia in Children: A Model of Precision Medicine and Chemotherapy-Free Therapy

Acute promyelocytic leukemia (APL) represents a paradigm of precision medicine. Indeed, in the last decades, the introduction of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) completely revolutionized the therapeutic approach to this previously highly fatal disorder. This entirely chemotherapy-free treatment, which provided excellent survival rates, has been initially validated in adults and, recently, translated in the pediatric setting. This review summarizes currently available data on the use of ATRA and ATO combination in pediatric APL, providing a particular focus on peculiar issues and challenges, such as the occurrence of pseudotumor cerebri and death during induction (early death), as well as the advantage offered by the ATO/ATRA combination in sparing long-term sequelae.

Does acute promyelocytic leukemia patient with the STAT5B/RARa fusion gene respond well to decitabine?: A case report and literature review

RATIONALE

Most acute promyelocytic leukemia (APL) patients respond to all-trans-retinoic acid (ATRA)and have a good prognosis. However, variants APL who carry PLZF/RARа, STAT5B/RARа, and STAT3/RARа are insensitive to ATRA and have poor prognoses. The standard treatment for variants APL is still unclear due to the small sample size.

PATIENT CONCERNS

Here we reported a Chinese male who was admitted to our hospital with the complaint of rib pain, dyspnea, and fever (37.5°C). Blood tests showed leukopenia (1.83 × 10/L), anemia (hemoglobin 73 g/L), and thrombocytopenia (54 × 10/L). Prothrombin time and activated partial thromboplastin time were normal.

DIAGNOSES

The patient was diagnosed as STAT5b-RARa-positive APL based on the clinical and laboratory findings.

INTERVENTIONS

ATRA was used immediately for induction treatment, then he was treated with ATRA + arsenic trioxide and got the severe cardiac insufficiency. Subsequently, consolidation chemotherapy was added with ATRA + Huangdai tablets + idarubicin and decitabine, cytarabine, aclamycin (DCAG).

OUTCOMES

The patient relapsed soon after his first molecular complete remission (CRm), fortunately, he got a second CRm with DCAG. He has survived for more than 9 months and remains CRm, now he is looking for a suitable donor to prepare for hematopoietic stem cell transplantation (HSCT).

LESSONS

APL patients with STAT5B-RARa is not only resistant to ATRA, but also to conventional combination chemotherapy such as daunorubicin and cytarabine/idarubicin and cytarabine or other regimens. Relapse and extramedullary infiltration is common, HSCT is a effective treatment, and the best time for HSCT is after the first CR. It should be noted that this patient got CRm with DCAG after relapse, so the role of decitabine in APL with STAT5B-RARa needs to be considered.

When Poisons Cure: The Case of Arsenic in Acute Promyelocytic Leukemia

Arsenic has been known for centuries for its double-edged potential: a poison and at the same time a therapeutic agent. The name "arsenikon," meaning "potent," speaks itself for the pharmaceutical properties of this compound, questioned and analyzed for at least 2000 years. In the last decades, acute promyelocytic leukemia (APL) has evolved from a highly fatal to a curable disease, due to the use of all-trans-retinoic acid and, more recently, arsenic trioxide combinations. The success of these entirely chemo-free regimens increased the awareness of APL and reduced the prevalence of early deaths, which was an impending issue in this disease. Further improvements are expected with the next use of oral arsenic formulations, which will allow a complete outpatient approach, at least in the post-induction settings, further improving patients' quality of life. The wide use of standardized approaches in APL will also help unravel long-standing open questions, including the pathogenesis, prevention, and treatment of the differentiation syndrome and of short-term organ toxicities. In the long term, the study of survivorship issues, such as fertility and organ-related and psychological damages, in the increasing number of survivors will help further improve their life after APL.

Classic and Variants APLs, as Viewed from a Therapy Response

Most acute promyelocytic leukemia (APL) are caused by PML-RARA, a translocation-driven fusion oncoprotein discovered three decades ago. Over the years, several other types of rare X-RARA fusions have been described, while recently, oncogenic fusion proteins involving other retinoic acid receptors (RARB or RARG) have been associated to very rare cases of acute promyelocytic leukemia. PML-RARA driven pathogenesis and the molecular basis for therapy response have been the focus of many studies, which have now converged into an integrated physio-pathological model. The latter is well supported by clinical and molecular studies on patients, making APL one of the rare hematological disorder cured by targeted therapies. Here we review recent data on APL-like diseases not driven by the PML-RARA fusion and discuss these in view of current understanding of "classic" APL pathogenesis and therapy response.

Acute Promyelocytic Leukemia: A Constellation of Molecular Events around a Single PML-RARA Fusion Gene

Although acute promyelocytic leukemia (APL) is one of the most characterized forms of acute myeloid leukemia (AML), the molecular mechanisms involved in the development and progression of this disease are still a matter of study. APL is defined by the PML-RARA rearrangement as a consequence of the translocation t(15;17)(q24;q21). However, this abnormality alone is not able to trigger the whole leukemic phenotype and secondary cooperating events might contribute to APL pathogenesis. Additional somatic mutations are known to occur recurrently in several genes, such as FLT3, WT1, NRAS and KRAS, whereas mutations in other common AML genes are rarely detected, resulting in a different molecular profile compared to other AML subtypes. How this mutational spectrum, including point mutations in the PML-RARA fusion gene, could contribute to the 10%–15% of relapsed or resistant APL patients is still unknown. Moreover, due to the uncertain impact of additional mutations on prognosis, the identification of the APL-specific genetic lesion is still the only method recommended in the routine evaluation/screening at diagnosis and for minimal residual disease (MRD) assessment. However, the gene expression profile of genes, such as ID1, BAALC, ERG, and KMT2E, once combined with the molecular events, might improve future prognostic models, allowing us to predict clinical outcomes and to categorize APL patients in different risk subsets, as recently reported. In this review, we will focus on the molecular characterization of APL patients at diagnosis, relapse and resistance, in both children and adults. We will also describe different standardized molecular approaches to study MRD, including those recently developed. Finally, we will discuss how novel molecular findings can improve the management of this disease.

Characterization of a rarely reported STAT5B/RARA gene fusion in a young adult with newly diagnosed acute promyelocytic leukemia with resistance to ATRA therapy

The detection of PML/RARA or variant RARA rearrangements is critical for the diagnosis and treatment of patients with newly diagnosed acute promyelocytic leukemia (APL). While most cases of APL harboring the PML/RARA fusion respond to all-trans retinoic acid (ATRA), some variant RARA rearrangements are ATRA insensitive. Herein, we report a 27-year-old male with newly diagnosed, rapidly progressive APL and a rarely described STAT5B/RARA fusion with known resistance to ATRA therapy. While the PML/RARA dual-color dual-fusion fluorescence in situ hybridization (FISH) probe study was negative, the RARA break-apart probe study revealed an atypical RARA rearrangement in 95% of nuclei. A next generation sequencing assay, mate-pair sequencing, was subsequently performed to further characterize the RARA rearrangement and identified the RARA gene fusion partner STAT5B.