Runx1 exon 6-related alternative splicing isoforms differentially regulate hematopoiesis in mice.

RUNX1 is an important transcription factor for hematopoiesis. There are multiple alternatively spliced isoforms of RUNX1. The best known isoforms are RUNX1a from use of exon 7A and RUNX1b and c from use of exon 7B. RUNX1a has unique functions due to its lack of C-terminal regions common to RUNX1b and c. Here, we report that the ortholog of human RUNX1a was only found in primates. Furthermore, we characterized 3 Runx1 isoforms generated by exon 6 alternative splicing. Runx1bEx6(-) (Runx1b without exon 6) and a unique mouse Runx1bEx6e showed higher colony-forming activity than the full-length Runx1b (Runx1bEx6(+)). They also facilitated the transactivation of Runx1bEx6(+). To gain insight into in vivo functions, we analyzed a knock-in (KI) mouse model that lacks isoforms Runx1b/cEx6(-) and Runx1bEx6e. KI mice had significantly fewer lineage-Sca1(+)c-Kit(+) cells, short-term hematopoietic stem cells (HSCs) and multipotent progenitors than controls. In vivo competitive repopulation assays demonstrated a sevenfold difference of functional HSCs between wild-type and KI mice. Together, our results show that Runx1 isoforms involving exon 6 support high self-renewal capacity in vitro, and their loss results in reduction of the HSC pool in vivo, which underscore the importance of fine-tuning RNA splicing in hematopoiesis.

Hes1 promotes blast crisis in chronic myelogenous leukemia through MMP-9 upregulation in leukemic cells.

High levels of HES1 expression are frequently found in BCR-ABL(+) chronic myelogenous leukemia in blast crisis (CML-BC). In mouse bone marrow transplantation (BMT) models, co-expression of BCR-ABL and Hes1 induces CML-BC-like disease; however, the underlying mechanism remained elusive. Here, based on gene expression analysis, we show that MMP-9 is upregulated by Hes1 in common myeloid progenitors (CMPs). Analysis of promoter activity demonstrated that Hes1 upregulated MMP-9 by activating NF-κB. Analysis of 20 samples from CML-BC patients showed that MMP-9 was highly expressed in three, with two exhibiting high levels of HES1 expression. Interestingly, MMP-9 deficiency impaired the cobblestone area-forming ability of CMPs expressing BCR-ABL and Hes1 that were in conjunction with a stromal cell layer. In addition, CMPs expressing BCR-ABL and Hes1 secreted MMP-9, promoting the release of soluble Kit-ligand (sKitL) from stromal cells, thereby enhancing proliferation of the leukemic cells. In accordance, mice transplanted with CMPs expressing BCR-ABL and Hes1 exhibited high levels of sKitL as well as MMP-9 in the serum. Importantly, MMP-9 deficiency impaired the development of CML-BC-like disease induced by BCR-ABL and Hes1 in mouse BMT models. The present results suggest that Hes1 promotes the development of CML-BC, partly through MMP-9 upregulation in leukemic cells.

Cooperation between RUNX1-ETO9a and novel transcriptional partner KLF6 in upregulation of Alox5 in acute myeloid leukemia.

Fusion protein RUNX1-ETO (AML1-ETO, RUNX1-RUNX1T1) is expressed as the result of the 8q22;21q22 translocation [t(8;21)], which is one of the most common chromosomal abnormalities found in acute myeloid leukemia. RUNX1-ETO is thought to promote leukemia development through the aberrant regulation of RUNX1 (AML1) target genes. Repression of these genes occurs via the recruitment of the corepressors N-COR and SMRT due to their interaction with ETO. Mechanisms of RUNX1-ETO target gene upregulation remain less well understood. Here we show that RUNX1-ETO9a, the leukemogenic alternatively spliced transcript expressed from t(8;21), upregulates target gene Alox5, which is a gene critically required for the promotion of chronic myeloid leukemia development by BCR-ABL. Loss of Alox5 expression reduces activity of RUNX1-ETO9a, MLL-AF9 and PML-RARα in vitro. However, Alox5 is not essential for the induction of leukemia by RUNX1-ETO9a in vivo. Finally, we demonstrate that the upregulation of Alox5 by RUNX1-ETO9a occurs via the C2H2 zinc finger transcription factor KLF6, a protein required for early hematopoiesis and yolk sac development. Furthermore, KLF6 is specifically upregulated by RUNX1-ETO in human leukemia cells. This identifies KLF6 as a novel mediator of t(8;21) target gene regulation, providing a new mechanism for RUNX1-ETO transcriptional control.

PRMT1 interacts with AML1-ETO to promote its transcriptional activation and progenitor cell proliferative potential.

Fusion protein AML1-ETO, resulting from t(8;21) translocation, is highly related to leukemia development. It has been reported that full-length AML1-ETO blocks AML1 function and requires additional mutagenic events to promote leukemia. We have previously shown that the expression of AE9a, a splice isoform of AML1-ETO, can rapidly cause leukemia in mice. To understand how AML1-ETO is involved in leukemia development, we took advantage of our AE9a leukemia model and sought to identify its interacting proteins from primary leukemic cells. Here, we report the discovery of a novel AE9a binding partner PRMT1 (protein arginine methyltransferase 1). PRMT1 not only interacts with but also weakly methylates arginine 142 of AE9a. Knockdown of PRMT1 affects expression of a specific group of AE9a-activated genes. We also show that AE9a recruits PRMT1 to promoters of AE9a-activated genes, resulting in enrichment of H4 arginine 3 methylation, H3 Lys9/14 acetylation, and transcription activation. More importantly, knockdown of PRMT1 suppresses the self-renewal capability of AE9a, suggesting a potential role of PRMT1 in regulating leukemia development.

Expression of the runt homology domain of RUNX1 disrupts homeostasis of hematopoietic stem cells and induces progression to myelodysplastic syndrome.

Mutations of RUNX1 are detected in patients with myelodysplastic syndrome (MDS). In particular, C-terminal truncation mutations lack a transcription regulatory domain and have increased DNA binding through the runt homology domain. The expression of the runt homology domain, RUNX1(41-214), in mouse hematopoietic cells induced progression to MDS and acute myeloid leukemia. Analysis of premyelodysplastic animals found expansion of c-Kit(+)Sca-1(+)Lin(-) cells and skewed differentiation to myeloid at the expense of the lymphoid lineage. These abnormalities correlate with the phenotype of Runx1-deficient animals, as expected given the reported dominant-negative role of C-terminal mutations over the full-length RUNX1. However, MDS is not observed in Runx1-deficient animals. Gene expression profiling found that RUNX1(41-214) c-Kit(+)Sca-1(+)Lin(-) cells have an overlapping yet distinct gene expression profile from Runx1-deficient animals. Moreover, an unexpected parallel was observed between the hematopoietic phenotype of RUNX1(41-214) and aged animals. Genes deregulated in RUNX1(41-214), but not in Runx1-deficient animals, were inversely correlated with the aging gene signature of HSCs, suggesting that disruption of the expression of genes related to normal aging by RUNX1 mutations contributes to development of MDS. The data presented here provide insights into the mechanisms of development of MDS in HSCs by C-terminal mutations of RUNX1.

Combined gene expression and DNA occupancy profiling identifies potential therapeutic targets of t(8;21) AML.

Chromosome translocation 8q22;21q22 [t(8;21)] is commonly associated with acute myeloid leukemia (AML), and the resulting AML1-ETO fusion proteins are involved in the pathogenesis of AML. To identify novel molecular and therapeutic targets, we performed combined gene expression microarray and promoter occupancy (ChIP-chip) profiling using Lin(-)/Sca1(-)/cKit(+) cells, the major leukemia cell population, from an AML mouse model induced by AML1-ETO9a (AE9a). Approximately 30% of the identified common targets of microarray and ChIP-chip assays overlap with the human t(8;21)-gene expression molecular signature. CD45, a protein tyrosine phosphatase and a negative regulator of cytokine/growth factor receptor and JAK/STAT signaling, is among those targets. Its expression is substantially down-regulated in leukemia cells. Consequently, JAK/STAT signaling is enhanced. Re-expression of CD45 suppresses JAK/STAT activation, delays leukemia development, and promotes apoptosis of t(8;21)-positive cells. This study demonstrates the benefit of combining gene expression and promoter occupancy profiling assays to identify molecular and potential therapeutic targets in human cancers and describes a previously unappreciated signaling pathway involving t(8;21) fusion proteins, CD45, and JAK/STAT, which could be a potential novel target for treating t(8;21) AML.

The molecular basis of myeloid malignancies.

Myeloid malignancies consist of acute myeloid leukemia (AML), myelodysplastic syndromes (MDS) and myeloproliferative neoplasm (MPN). The latter two diseases have preleukemic features and frequently evolve to AML. As with solid tumors, multiple mutations are required for leukemogenesis. A decade ago, these gene alterations were subdivided into two categories: class I mutations stimulating cell growth or inhibiting apoptosis; and class II mutations that hamper differentiation of hematopoietic cells. In mouse models, class I mutations such as the Bcr-Abl fusion kinase induce MPN by themselves and some class II mutations such as Runx1 mutations induce MDS. Combinations of class I and class II mutations induce AML in a variety of mouse models. Thus, it was postulated that hematopoietic cells whose differentiation is blocked by class II mutations would autonomously proliferate with class I mutations leading to the development of leukemia. Recent progress in high-speed sequencing has enabled efficient identification of novel mutations in a variety of molecules including epigenetic factors, splicing factors, signaling molecules and proteins in the cohesin complex; most of these are not categorized as either class I or class II mutations. The functional consequences of these mutations are now being extensively investigated. In this article, we will review the molecular basis of hematological malignancies, focusing on mouse models and the interfaces between these models and clinical findings, and revisit the classical class I/II hypothesis.

Two types of C/EBPα mutations play distinct but collaborative roles in leukemogenesis: lessons from clinical data and BMT models.

Two types of mutations of a transcription factor CCAAT-enhancer binding protein α (C/EBPα) are found in leukemic cells of 5%-14% of acute myeloid leukemia (AML) patients: N-terminal mutations expressing dominant negative p30 and C-terminal mutations in the basic leucine zipper domain. Our results showed that a mutation of C/EBPα in one allele was observed in AML after myelodysplastic syndrome, while the 2 alleles are mutated in de novo AML. Unlike an N-terminal frame-shift mutant (C/EBPα-N(m))-transduced cells, a C-terminal mutant (C/EBPα-C(m))-transduced cells alone induced AML with leukopenia in mice 4-12 months after bone marrow transplantation. Coexpression of both mutants induced AML with marked leukocytosis with shorter latencies. Interestingly, C/EBPα-C(m) collaborated with an Flt3-activating mutant Flt3-ITD in inducing AML. Moreover, C/EBPα-C(m) strongly blocked myeloid differentiation of 32Dcl3 cells, suggesting its class II mutation-like role in leukemogenesis. Although C/EBPα-C(m) failed to inhibit transcriptional activity of wild-type C/EBPα, it suppressed the synergistic effect between C/EBPα and PU.1. On the other hand, C/EBPα-N(m) inhibited C/EBPα activation in the absence of PU.1, despite low expression levels of p30 protein generated by C/EBPα-N(m). Thus, 2 types of C/EBPα mutations are implicated in leukemo-genesis, involving different and cooperating molecular mechanisms.

Transforming growth factor-ß-stimulated clone-22 is a negative-feedback regulator of Ras / Raf signaling: Implications for tumorigenesis.

Transforming growth factor-ß (TGF-ß)-stimulated clone-22 (TSC-22), also called TSC22D1-2, is a putative tumor suppressor. We previously identified TSC-22 downstream of an active mutant of fms-like tyrosine kinase-3 (Flt3). Here, we show that TSC-22 works as a tumor suppressor through inhibiting Ras/Raf signaling. Notably, TSC-22 was upregulated by Ras/Raf activation, whereas its upregulation was inhibited by concurrent STAT5 activation. Although TSC-22 was normally retained in the cytoplasm by its nuclear export signal (NES), Ras/Raf activation caused nuclear translocation of TSC-22, but not TSC22D1-1. Unlike glucocorticoid-induced leucine zipper (GILZ/TSC22D3-2) previously characterized as a negative regulator of Ras/Raf signaling, TSC-22 failed to interact physically with Ras/Raf. Importantly, transduction with TSC-22, but not TSC22D1-1, suppressed the growth, transformation and tumorigenesis of NIH3T3 cells expressing oncogenic H-Ras: this suppression was enhanced by transduction with a TSC-22 mutant lacking NES that had accumulated in the nucleus. Collectively, upregulation and nuclear translocation of TSC-22 played an important role in the feedback suppression of Ras/Raf signaling. Consistently, TSC22D1-deficient mice were susceptible to tumorigenesis in a mouse model of chemically-induced liver tumors bearing active mutations of Ras/Raf. Thus, TSC-22 negatively regulated Ras/Raf signaling through a mechanism different from GILZ, implicating TSC-22 as a novel suppressor of oncogenic Ras/Raf-induced tumors.

Hes1 immortalizes committed progenitors and plays a role in blast crisis transition in chronic myelogenous leukemia.

Hairy enhancer of split 1 (Hes1) is a basic helix-loop-helix transcriptional repressor that affects differentiation and often helps maintain cells in an immature state in various tissues. Here we show that retroviral expression of Hes1 immortalizes common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) in the presence of interleukin-3, conferring permanent replating capability on these cells. Whereas these cells did not develop myeloproliferative neoplasms when intravenously administered to irradiated mice, the combination of Hes1 and BCR-ABL in CMPs and GMPs caused acute leukemia resembling blast crisis of chronic myelogenous leukemia (CML), resulting in rapid death of the recipient mice. On the other hand, BCR-ABL alone caused CML-like disease when expressed in c-Kit-positive, Sca-1-positive, and lineage-negative hematopoietic stem cells (KSLs), but not committed progenitors CMPs or GMPs, as previously reported. Leukemic cells derived from Hes1 and BCR-ABL-expressing CMPs and GMPs were more immature than those derived from BCR-ABL-expressing KSLs. Intriguingly, Hes1 was highly expressed in 8 of 20 patients with CML in blast crisis, but not in the chronic phase, and dominant negative Hes1 retarded the growth of some CML cell lines expressing Hes1. These results suggest that Hes1 is a key molecule in blast crisis transition in CML.

Atypical Splenic Abscesses Due to Clostridioides difficile.

BACKGROUND Splenic abscess is a rare infectious disease that occurs after bloodstream infection and trauma. It has become more common due to an increase in the number of immunocompromised patients. They typically present with round cystic lesions demonstrated by ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI). Clostridioides difficile (formerly Clostridium difficile) is a well-known cause of pseudomembranous colitis, but extraintestinal manifestations are very rare. To the best of our knowledge, only 9 cases of splenic abscess due to C. difficile have been reported in the literature. CASE REPORT A 90-year-old man presented with weight loss, fever, and abdominal pain. Contrast-enhanced CT revealed splenomegaly with irregular hypodense nodules. Image-guided biopsy or drainage was not performed for a technical reason. MRI showed atypical nodules with mixed high and low signals on both T1- and T2-weighted images, which were inconclusive. A laparoscopic splenectomy was performed, which resulted in partial removal due to severe adhesion of the spleen to the surrounding tissues. Cultures of splenic pus yielded C. difficile, Enterococcus faecium, and Bacteroides fragilis. Pathological examination of the spleen showed widespread abscesses with hemorrhage and necrosis, leading to the diagnosis of splenic abscesses. Intravenous administration of vancomycin, clindamycin or metronidazole was ineffective. He died of fatal arrhythmia 5 months after the initial diagnosis of splenic abscess. CONCLUSIONS Splenic abscess can present with atypical imaging findings owing to chronic inflammation, bleeding, and necrosis. Although polymicrobial, this is the tenth reported case of splenic abscess caused by C. difficile.

Enhanced expression of p210BCR/ABL and aberrant expression of Zfp423/ZNF423 induce blast crisis of chronic myelogenous leukemia.

Chronic myelogenous leukemia (CML) is a hematopoietic disorder originating from p210BCR/ABL-transformed stem cells, which begins as indolent chronic phase (CP) but progresses into fatal blast crisis (BC). To investigate molecular mechanism(s) underlying disease evolution, CML-exhibiting p210BCR/ABL transgenic mice were crossed with BXH2 mice that transmit a replication-competent retrovirus. Whereas nontransgenic mice in the BXH2 background exclusively developed acute myeloid leukemia, p210BCR/ABL transgenic littermates developed nonmyeloid leukemias, in which inverse polymerase chain reaction detected 2 common viral integration sites (CISs). Interestingly, one CIS was transgene's own promoter, which up-regulated p210BCR/ABL expression. The other was the 5' noncoding region of a transcription factor, Zfp423, which induced aberrant Zfp423 expression. The cooperative activities of Zfp423 and p210BCR/ABL were demonstrated as follows: (1) introduction of Zfp423 in p210BCR/ABL transgenic bone marrow (BM) cells increased colony-forming ability, (2) suppression of ZNF423 (human homologue of Zfp423) in ZNF423-expressing, p210BCR/ABL-positive hematopoietic cells retarded cell growth, (3) mice that received a transplant of BM cells transduced with Zfp423 and p210BCR/ABL developed acute leukemia, and (4) expression of ZNF423 was found in human BCR/ABL-positive cell lines and CML BC samples. These results demonstrate that enhanced expression of p210BCR/ABL and deregulated expression of Zfp423/ZNF423 contribute to CML BC.

Anorectal Abscess in a Patient with Neutropenia and Refractory Acute Myeloid Leukemia: To Operate or not to Operate?

BACKGROUND Anorectal infections occur in 5% to 9% of patients with hematological malignancies, including acute myeloid leukemia, and cause febrile neutropenia and sepsis. Surgical treatments of anorectal abscesses tend to be avoided in patients with leukemia owing to persistent neutropenia and bleeding risks. CASE REPORT A 56-year-old man presented with an ischiorectal abscess. Preoperative laboratory test results revealed leukocytopenia and anemia. He was diagnosed with acute myeloid leukemia. He developed septic shock. Antibiotic treatment was ineffective, and fever persisted. One week later, the abscess was treated by incision and drainage. Two days later, induction chemotherapy was initiated. No pus was drained; cellulitis spread to both buttocks. Pain worsened, and oxycodone was administered. Achievement of complete remission failed. Reinduction therapy was started, followed by fistulotomy of the abscess with extensive debridement of cellulitis on day 6. Granulation was observed on day 17. The patient's fever resolved on day 21. Although hematopoietic recovery was observed, bone marrow examination demonstrated partial remission. Two additional courses of chemotherapy were administered. Abscess recurrence was not observed, even during febrile neutropenia. The surgical wound shrank to a skin defect along the gluteal cleft. He achieved complete remission and was transferred to another hospital, where he underwent 3 allogeneic stem cell transplants. He died of leukemia progression. CONCLUSIONS Surgical treatments can prevent fatal progression of anorectal abscess, even during neutropenia. Incision and drainage are suitable for fluctuant abscesses. For a non-fluctuant abscess aggravated by sepsis and cellulitis, it is worth considering more invasive surgical interventions, including debridement and fistulotomy.

Molecular bases of myelodysplastic syndromes: lessons from animal models.

Myelodysplastic syndrome (MDS) is a clonal disorder of hematopietic stem cells characterized by ineffective hematopoiesis, peripheral blood cytopenia, morphologic dysplasia, and susceptibility to acute myeloid leukemia. Several mechanisms have been suggested as causes of MDS: unbalanced chromosomal abnormalities reflecting a gain or loss of chromosomal material, point mutations of transcription factors, and inactivation of p53. However, appropriate animal models that mimic MDS have long been lacking. We recently reported a novel murine model of MDS that recapitulates trilineage dysplasia and transformation to AML. In this review, we summarize the animal models of MDS and discuss the molecular bases of MDS as well as those of leukemia and myeloproliferative disorders (MPD). J. Cell. Physiol. 219: 529-534, 2009. (c) 2009 Wiley-Liss, Inc.

Hemophagocytic Syndrome-Associated Variant of Methotrexate-Associated Intravascular Large B-Cell Lymphoma in a Rheumatoid Arthritis Patient.

A 59-year-old man was treated for rheumatoid arthritis (RA) for 12 years with methotrexate (MTX) and prednisolone. After MTX-associated interstitial pneumonia developed, he was treated with cyclophosphamide and prednisolone for 7 months. Arthritis worsened, and tacrolimus was added to the treatment regimen. One month later, he had fever, loss of appetite, and dyspnea on exertion. Blood tests showed pancytopenia with large, atypical lymphocytes. Computed tomography showed mild splenomegaly. Bone marrow examination demonstrated CD20-positive, EBER-positive atypical lymphocytes, and hemophagocytosis. Random skin biopsy led to the diagnosis of intravascular large B-cell lymphoma (IVLBCL). The final diagnosis was a hemophagocytic syndrome-associated variant of IVLBCL. Complete remission was achieved after seven courses of R-CHOP. However, within a month, he complained of dizziness. Magnetic resonance imaging revealed focal infarctions in the cerebellum and around the left lateral ventricle. Central nervous system relapse was suspected. Although salvage chemotherapy (CHASER), whole brain irradiation, and intrathecal injection of cytarabine and prednisolone were temporarily effective, he died. Autopsy revealed infiltration of lymphoma cells in the brain and adrenal glands. To the best of our knowledge, this is the sixth case of IVLBCL and the first case of the hemophagocytic syndrome-associated variant of IVLBCL in RA patients in the literature.

Prolonged Myelosuppression due to Progressive Bone Marrow Fibrosis in a Patient with Acute Promyelocytic Leukemia.

A 34-year-old woman was diagnosed with acute promyelocytic leukemia. Chemotherapy was administered following the JALSG APL204 protocol. Induction therapy with all-trans retinoic acid resulted in complete remission on day 49. She developed coccygeal pain from day 18, which spread to the spine and cheekbones and lasted 5 weeks. She had similar bone pain on days 7-10 of the first consolidation therapy and on days 4-12 of the second consolidation therapy. Oral loxoprofen was prescribed for pain relief. On day 33 of the third consolidation, white blood cell and neutrophil counts were 320/µL and 20/µL, respectively. After she developed epigastralgia and hematemesis, she developed septic shock. Gastroendoscopy revealed markedly thickened folds and diffusely damaged mucosa with blood oozing. Computed tomography revealed thickened walls of the antrum and the pylorus. Despite emergency treatments, she died. Bacterial culture of the gastric fluid yielded Enterobacter cloacae and enterococci growth. Collectively, she was diagnosed with phlegmonous gastritis. Retrospective examination of serial bone marrow biopsy specimens demonstrated progressive bone marrow fibrosis, which may have caused prolonged myelosuppression. Thus, evaluation of bone marrow fibrosis by bone marrow biopsy after each treatment cycle might serve as a predictor of persistent myelosuppression induced by chemotherapy.

Secondary Syphilis with Tonsillar and Cervical Lymphadenopathy and a Pulmonary Lesion Mimicking Malignant Lymphoma.

BACKGROUND Syphilis is a sexually transmitted disease caused by the pathogen Treponema pallidum. Prevalence continues to rise, especially among men who have sex with men (MSM). Due to changes in patterns of sexual activity, manifestations of the disease are highly variable. CASE REPORT A 27-year-old male visited the hospital for a low-grade fever and tender 5-cm mass in the right side of his neck. His right tonsil was swollen and covered with a white coating. Levofloxacin was prescribed, but ineffective. The patient's levels of liver function enzymes increased gradually. Systemic magnetic resonance imaging (MRI) revealed bilateral cervical lymphadenopathy with right predominance, a right pulmonary nodule, and a periportal lymph node, suggestive of malignant lymphoma. However, a biopsy of the right cervical lymph node showed nonspecific inflammation. Preoperative rapid plasma reagin (RPR) and T. pallidum latex agglutination (TPLA) tests were positive. The patient was MSM and reported oral sex with many sexual partners. A diagnosis of secondary syphilis was made. Oral amoxicillin was effective, and all symptoms other than periportal lymph node resolved. CONCLUSIONS Tonsillitis, cervical lymphadenopathy, and lung lesions can be manifestations of secondary syphilis. A detailed history, pathology, and serology are crucial for diagnosis.

Splenic Marginal Zone Lymphoma with Acquired von Willebrand Syndrome Diagnosed via Splenic Bleeding.

An 85-year-old woman underwent emergent splenectomy due to left abdominal pain and active bleeding in a massively enlarged spleen. The histological diagnosis was splenic marginal zone lymphoma (SMZL). A prolonged activated partial thromboplastin time (APTT) was noted, and additional tests led to the diagnosis of type 2A-like acquired von Willebrand syndrome (AVWS). An APTT cross mixing test ruled out the presence of inhibitors. She received eight courses of rituximab monotherapy. The coagulation data showed no improvement, possibly because the lymphoma showed a poor response to the treatment. AVWS rarely causes bleeding in solid organs. This is the first case of SMZL with AVWS diagnosed via splenic bleeding.

Bosutinib as a fourth-line therapy for a patient with T315I-positive lymphoid blastic phase chronic myeloid leukemia: A case report.

A 35-year-old male was diagnosed with chronic myeloid leukemia in the chronic phase and was prescribed 100 mg daily dasatinib. However, dasatinib was discontinued due to thrombocytopenia, and within six months, the disease progressed to the lymphoid blastic phase. Hyper-cyclophosphamide, vincristine, adriamycin and dexamethasone chemotherapy combined with 140 mg dasatinib or 600 mg imatinib was prescribed. The two inhibitors were soon discontinued due to severe thrombocytopenia and jaundice, respectively. Myelosuppression persisted subsequent to the nadir. Bone marrow (BM) aspiration and biopsy revealed hypercellular marrow filled with blasts. Sequencing of the leukemia cells revealed overlapping peaks for the wild-type sequence and the T315I mutant sequence. The patient was treated with 500 mg bosutinib (which was later reduced to 300 mg) for pretransplant cytoreduction. After 5 months, the patient's spleen exhibited a reduction in volume and the percentage of blasts in the BM decreased from 96.1 to 17.5%. The patient successfully underwent cord blood transplantation. The patient has been disease-free for 5 months subsequent to transplantation. This case suggests that bosutinib may be effective for cytoreduction prior to stem cell transplantation, unless the leukemia cells consistently harbor the T315I mutation.