Conventional cytogenetics in myelofibrosis: literature review and discussion

Primary myelofibrosis: 2012 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by stem cell-derived clonal myeloproliferation, abnormal cytokine expression, bone marrow fibrosis, anemia, splenomegaly, extramedullary hematopoiesis (EMH), constitutional symptoms, cachexia, leukemic progression, and shortened survival.

DIAGNOSIS

Diagnosis is based on bone marrow morphology. The presence of fibrosis, JAK2/MPL mutation or +9/13q- cytogenetic abnormality is supportive but not essential for diagnosis. Prefibrotic PMF mimics essential thrombocythemia in its presentation and the distinction is prognostically relevant. Differential diagnosis of myelofibrosis should include chronic myelogenous leukemia, myelodysplastic syndromes, chronic myelomonocytic leukemia, and acute myeloid leukemia.

RISK STRATIFICATION

The Dynamic International Prognostic Scoring System-plus (DIPSS-plus) prognostic model for PMF can be applied at any point during the disease course and uses eight independent predictors of inferior survival: age >65 years, hemoglobin <10 g/dL, leukocytes >25 × 10(9) /L, circulating blasts ≥1%, constitutional symptoms, red cell transfusion dependency, platelet count <100 × 10(9) /L, and unfavorable karyotype (i.e., complex karyotype or sole or two abnormalities that include +8, -7/7q-, i(17q), inv(3), -5/5q-, 12p- or 11q23 rearrangement). The presence of 0, 1, "2 or 3," and ≥4 adverse factors defines low, intermediate-1, intermediate-2, and high-risk disease with median survivals of ~15.4, 6.5, 2.9, and 1.3 years, respectively. A >80% two-year mortality is predicted by monosomal karyotype, inv(3)/i(17q) abnormalities, or any two of circulating blasts >9%, leukocytes ≥40 × 10(9) /L or other unfavorable karyotype.

RISK-ADAPTED THERAPY

Observation alone is adequate for asymptomatic low/intermediate-1 risk disease. Allogeneic stem cell transplantation or experimental drug therapy is considered for intermediate-2/ high risk disease. Conventional or experimental drug therapy is reasonable for symptomatic intermediate-1 risk disease. Splenectomy and low-dose radiotherapy are used for drug-refractory splenomegaly. Radiotherapy is also used for the treatment of non-hepatosplenic EMH, PMF-associated pulmonary hypertension, and extremity bone pain.

SNPs array karyotyping reveals a novel recurrent 20p13 amplification in primary myelofibrosis

The molecular pathogenesis of primary mielofibrosis (PMF) is still largely unknown. Recently, single-nucleotide polymorphism arrays (SNP-A) allowed for genome-wide profiling of copy-number alterations and acquired uniparental disomy (aUPD) at high-resolution. In this study we analyzed 20 PMF patients using the Genome-Wide Human SNP Array 6.0 in order to identify novel recurrent genomic abnormalities. We observed a complex karyotype in all cases, detecting all the previously reported lesions (del(5q), del(20q), del(13q), +8, aUPD at 9p24 and abnormalities on chromosome 1). In addition, we identified several novel cryptic lesions. In particular, we found a recurrent alteration involving cytoband 20p13 in 55% of patients. We defined a minimal affected region (MAR), an amplification of 9,911 base-pair (bp) overlapping the SIRPB1 gene locus. Noteworthy, by extending the analysis to the adjacent areas, the cytoband was overall affected in 95% of cases. Remarkably, these results were confirmed by real-time PCR and validated in silico in a large independent series of myeloproliferative diseases. Finally, by immunohistochemistry we found that SIRPB1 was over-expressed in the bone marrow of PMF patients carrying 20p13 amplification. In conclusion, we identified a novel highly recurrent genomic lesion in PMF patients, which definitely warrant further functional and clinical characterization.

Genome integrity of myeloproliferative neoplasms in chronic phase and during disease progression

Philadelphia chromosome–negative myeloproliferative neoplasms (MPNs) are clonal myeloid disorders with increased production of terminally differentiated cells. The disease course is generally chronic, but some patients show disease progression (secondary myelofibrosis or accelerated phase) and/or leukemic transformation. We investigated chromosomal aberrations in 408 MPN samples using high-resolution single-nucleotide polymorphism microarrays to identify disease-associated somatic lesions. Of 408 samples, 37.5% had a wild-type karyotype and 62.5% harbored at least 1 chromosomal aberration. We identified 25 recurrent aberrations that were found in 3 or more samples. An increased number of chromosomal lesions was significantly associated with patient age, as well as with disease progression and leukemic transformation, but no association was observed with MPN subtypes, Janus kinase 2 (JAK2) mutational status, or disease duration. Aberrations of chromosomes 1q and 9p were positively associated with disease progression to secondary myelofibrosis or accelerated phase. Changes of chromosomes 1q, 7q, 5q, 6p, 7p, 19q, 22q, and 3q were positively associated with post-MPN acute myeloid leukemia. We mapped commonly affected regions to single target genes on chromosomes 3p (forkhead box P1 [FOXP1]), 4q (tet oncogene family member 2 [TET2]), 7p (IKAROS family zinc finger 1 [IKZF1]), 7q (cut-like homeobox 1 [CUX1]), 12p (ets variant 6 [ETV6]), and 21q (runt-related transcription factor 1 [RUNX1]). Our data provide insight into the genetic complexity of MPNs and implicate new genes involved in disease progression.

Disruption of the ASXL1 gene is frequent in primary, post-essential thrombocytosis and post-polycythemia vera myelofibrosis, but not essential thrombocytosis or polycythemia vera: analysis of molecular genetics and clinical phenotypes

BACKGROUND

The myeloproliferative neoplasms, essential thrombocytosis, polycythemia vera and primary myelofibrosis, share the same acquired genetic lesion, but the concept of JAK2 V617F serving as the sole lesion responsible for these neoplasms is under question, and there has been interest in identifying additional mutations that may contribute to disease pathogenesis. Because ASXL1 lesions have been increasingly identified in myeloid neoplasms, we examined the relationships of ASXL1 mutation or deletion to both clinical phenotype and associated molecular features in 166 patients with myeloproliferative neoplasms.

DESIGN AND METHODS

Exon 12 of ASXL1 was amplified from neutrophil genomic DNA and bidirectionally sequenced in 77 patients with myelofibrosis (including patients with primary and post-essential thrombocytosis or post-polycythemia myelofibrosis), 42 patients with polycythemia vera, 41 with essential thrombocytosis and 6 with post-myelofibrosis acute myeloid leukemia. Pyrosequencing assays were designed to determine the allele percentages of JAK2 V617F (G5073770T), ASXL1 2475dupA, and ASXL1 2846_2847del in neutrophil genomic DNA samples. Clinical and laboratory characteristics of patients with wild-type and ASXL1 mutations were then compared.

RESULTS

We identified nonsense mutations or hemizygous deletion of ASXL1 in 36% of the patients with myelofibrosis, but very rarely among those with polycythemia vera or essential thrombocytosis. Among the patients with myelofibrosis, those with ASXL1 lesions were not distinguished from their wild-type counterparts with regard to JAK2 V617F status, exposure to chemotherapy or evolution to leukemia. Myelofibrosis patients with ASXL1 lesions were more likely to have received anemia-directed therapy compared to those without lesions [15/26 (58%) versus 11/39 (23%); P=0.02]. Using serial banked samples and quantitative ASXL1 mutant allele burden assays, we observed the acquisition and accumulation of ASXL1 mutations over time in two patients with post-essential thrombocytosis myelofibrosis.

CONCLUSIONS

ASXL1 haploinsufficiency is associated with a myelofibrosis phenotype in the context of other known and unknown lesions, and disruption of ASXL1 function may contribute to the disease pathogenesis of myelofibrosis.

Myeloid blastic transformation of myeloproliferative neoplasms--a review of 112 cases

Blastic transformation of myeloproliferative neoplasms (MPN) is still poorly understood. We describe a cohort of 23 Roswell Park Cancer Institute (RPCI) patients and 89 additional cases from the English literature for whom biologic features were described. We initially compared our 23 patients to the 89 cases from the literature. Our population had significantly less patients with prior history of polycythemia vera (PV), shorter time from MPN diagnosis to blastic transformation, <3 prior therapies, more frequent use of hydroxyurea and erythropoietin and less frequent use of alkylating agents. Interestingly, the overall survival of the two cohorts from the time of blastic transformation was similar. We therefore looked at the outcome of the entire cohort (n=112). Patients with prior history of essential thrombocythemia survived longer than patients with prior history of myelofibrosis or PV. Further, patients with <3 prior therapies, those who lacked complex karyotype and those <60 year old at MPN diagnosis had significantly longer survival. Among the PRCI population, 20/23 patients underwent induction treatment with cytarabine and an anthracycline containing regimens; 12 achieved remission and their overall survival was significantly longer than those who did not. Three patients underwent an allogeneic transplantation and their survival was significantly longer than those who did not. Patients with <3 prior therapies, those who lack complex karyotype and those <60 at MPN diagnosis have longer survival following blastic transformation. Finally, allogeneic transplantation represents the only chance for long-term survival in these patients.

Cytogenetics of myeloproliferative neoplasms

The introduction of JAK2 mutation testing has changed dramatically the diagnostic algorithms for myeloproliferative neoplasms (MPNs) but there is still a place for conventional cytogenetic analysis in the initial work-up of MPN cases, particularly as this group of myeloid disorders has been expanded to include chronic eosinophilic leukaemia and myeloid neoplasms with abnormalities of the PDGFRA, PDGFRB, and FGFR1 genes. Mastocytosis is also included under the umbrella of MPN but the cytogenetic abnormalities observed usually reflect any associated clonal haematological non-mast cell lineage disease.

Frequency of heterozygous TET2 deletions in myeloproliferative neoplasms

The Philadelphia chromosome (Ph)-negative myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia, and primary myelofibrosis, are a group of clonal hematopoietic stem cell disorders with overlapping clinical and cytogenetic features and a variable tendency to evolve into acute leukemia. These diseases not only share overlapping chromosomal abnormalities but also a number of acquired somatic mutations. Recently, mutations in a putative tumor suppressor gene, ten-eleven translocation 2 (TET2) on chromosome 4q24 have been identified in 12% of patients with MPN. Additionally 4q24 chromosomal rearrangements in MPN, including TET2 deletions, have also been observed using conventional cytogenetics. The goal of this study was to investigate the frequency of genomic TET2 rearrangements in MPN using fluorescence in situ hybridization as a more sensitive method for screening and identifying genomic deletions. Among 146 MPN patients, we identified two patients (1.4%) who showed a common 4q24 deletion, including TET2. Our observations also indicated that the frequency of TET2 deletion is increased in patients with an abnormal karyotype (5%).

Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1

Myeloproliferative neoplasms (MPNs) originate from genetically transformed hematopoietic stem cells that retain the capacity for multilineage differentiation and effective myelopoiesis. Beginning in early 2005, a number of novel mutations involving Janus kinase 2 (JAK2), Myeloproliferative Leukemia Virus (MPL), TET oncogene family member 2 (TET2), Additional Sex Combs-Like 1 (ASXL1), Casitas B-lineage lymphoma proto-oncogene (CBL), Isocitrate dehydrogenase (IDH) and IKAROS family zinc finger 1 (IKZF1) have been described in BCR-ABL1-negative MPNs. However, none of these mutations were MPN specific, displayed mutual exclusivity or could be traced back to a common ancestral clone. JAK2 and MPL mutations appear to exert a phenotype-modifying effect and are distinctly associated with polycythemia vera, essential thrombocythemia and primary myelofibrosis; the corresponding mutational frequencies are approximately 99, 55 and 65% for JAK2 and 0, 3 and 10% for MPL mutations. The incidence of TET2, ASXL1, CBL, IDH or IKZF1 mutations in these disorders ranges from 0 to 17%; these latter mutations are more common in chronic (TET2, ASXL1, CBL) or juvenile (CBL) myelomonocytic leukemias, mastocytosis (TET2), myelodysplastic syndromes (TET2, ASXL1) and secondary acute myeloid leukemia, including blast-phase MPN (IDH, ASXL1, IKZF1). The functional consequences of MPN-associated mutations include unregulated JAK-STAT (Janus kinase/signal transducer and activator of transcription) signaling, epigenetic modulation of transcription and abnormal accumulation of oncoproteins. However, it is not clear as to whether and how these abnormalities contribute to disease initiation, clonal evolution or blastic transformation.

Aberrant myeloid maturation identified by flow cytometry in primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm that may display a variable degree of cytopenia and dysplasia sometimes difficult to distinguish from myelodysplastic syndrome with myelofibrosis (MDS-MF). We reviewed flow cytometric features of bone marrow from 70 cases of PMF and compared them with those from 17 cases of MDS-MF and 20 nonneoplastic control cases. The results were correlated with JAK2(V617F) and cytogenetic findings. Granulocytes and monocytes from PMF cases exhibited multiple dysplastic features overlapping with those of MDS-MF at a comparable or higher frequency: low side scattering, aberrant CD56 expression in granulocytes and monocytes, and an abnormal CD13/CD16 maturation pattern. Unique to PMF was the small granulocyte size compared with that of MDS-MF and control cases. Although the percentage of CD56+ granulocytes and monocytes did not correlate with JAK2(V617F) or cytogenetic abnormalities, a subset analysis of 36 cases revealed that median fluorescence intensity of CD56 expression correlated positively with the presence of cytogenetic abnormalities. Our findings indicate that although there is considerable overlap between PMF and MDS-MF, the smaller granulocytes observed in PMF are a useful distinguishing feature.

Improved outcomes using tacrolimus/sirolimus for graft-versus-host disease prophylaxis with a reduced-intensity conditioning regimen for allogeneic hematopoietic cell transplant as treatment of myelofibrosis

Allogeneic hematopoietic cell transplantation (HCT) using reduced-intensity conditioning (RIC) regimens is a potentially curative treatment for patients (patients) with myelofibrosis (MF), as we and others have reported. Nonrelapse mortality (NRM) from graft-versus-host disease (GVHD) and other complications has limited the success of this approach. As part of an ongoing prospective research study at City of Hope, a combination of tacrolimus/sirolimus +/- methotrexate (MTX) for GVHD prophylaxis has become the standard treatment for our allogeneic HCT patients. In this report, we present results for 23 consecutive patients, including extended follow up for 9 patients previously reported who received cyclosporine (CsA)/mycophenolate moffetil (MMF)+/-MTX, and the current series of 14 patients who received tacrolimus/sirolimus+/-MTX, and evaluate the impact of the GVHD prophylaxis regimen on the outcomes. Median follow-up for alive patients was 29.0 months (9.5-97.0). The estimated 2-year overall survival (OS) for the CsA/MMF cohort was 55.6% (confidence interval 36.0, 71.3), and for the tacrolimus/sirolimus cohort it was 92.9% (63.3, 98.8) (P=.047). The probability of grade III or IV acute GVHD (aGVHD) was 60% for the CsA/MMF patients, and 10% for the tacrolimus/sirolimus group (P=.0102). No significant differences were seen for grade II to IV aGVHD in the 2 groups. We conclude that the combination of tacrolimus/sirolimus+/-MTX for GVHD prophylaxis in the setting of RIC HCT for MF appears to reduce the incidence of severe aGVHD and NRM, and leads to improved OS compared to CSA/MMF+/-MTX.