Long-term survival of infants with idiopathic myelofibrosis

Congenital macrothrombocytopenia with focal myelofibrosis due to mutations in human G6b-B is rescued in humanized mice

Unlike primary myelofibrosis (PMF) in adults, myelofibrosis in children is rare. Congenital (inherited) forms of myelofibrosis (cMF) have been described, but the underlying genetic mechanisms remain elusive. Here we describe 4 families with autosomal recessive inherited macrothrombocytopenia with focal myelofibrosis due to germ line loss-of-function mutations in the megakaryocyte-specific immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptor G6b-B (G6b, C6orf25, or MPIG6B). Patients presented with a mild-to-moderate bleeding diathesis, macrothrombocytopenia, anemia, leukocytosis and atypical megakaryocytes associated with a distinctive, focal, perimegakaryocytic pattern of bone marrow fibrosis. In addition to identifying the responsible gene, the description of G6b-B as the mutated protein potentially implicates aberrant G6b-B megakaryocytic signaling and activation in the pathogenesis of myelofibrosis. Targeted insertion of human G6b in mice rescued the knockout phenotype and a copy number effect of human G6b-B expression was observed. Homozygous knockin mice expressed 25% of human G6b-B and exhibited a marginal reduction in platelet count and mild alterations in platelet function; these phenotypes were more severe in heterozygous mice that expressed only 12% of human G6b-B. This study establishes G6b-B as a critical regulator of platelet homeostasis in humans and mice. In addition, the humanized G6b mouse will provide an invaluable tool for further investigating the physiological functions of human G6b-B as well as testing the efficacy of drugs targeting this receptor.

A Rare Case of Primary Myelofibrosis in a 14-Year-Old Patient With Congenital Asplenia

Primary myelofibrosis (PMF) is rarely diagnosed in children, and in most cases in children younger than 3 years old. Pediatric PMF generally follows a benign course and is usually managed supportively with blood transfusions and prophylactic antibiotics for infections. We present a case of a 17-year-old girl diagnosed with PMF at the age of 14 years. A computed tomography scan performed at the time of an appendectomy showed congenital asplenism. To our knowledge, this is only the third case of myelofibrosis and congenital asplenism to be reported in the literature. Whether asplenism contributed to the development of myelofibrosis is not known.

Myeloproliferative Neoplasms in Children

Myeloproliferative neoplasms (MPN) are a group of clonal hematopoietic stem cell disorders characterized by aberrant proliferation of one or more myeloid lineages often with increased immature cells in the peripheral blood. The three classical BCR-ABL-negative MPNs are: 1) polycythemia vera (PV), 2) essential thrombocythemia (ET), and 3) primary myelofibrosis (PMF), which are typically disorders of older adults and are exceedingly rare in children. The diagnostic criteria for MPNs remain largely defined by clinical, laboratory and histopathology assessments in adults, but they have been applied to the pediatric population. The discovery of the JAK2 V617F mutation, and more recently, MPL and CALR mutations, are major landmarks in the understanding of MPNs. Nevertheless, they rarely occur in children, posing a significant diagnostic challenge given the lack of an objective, clonal marker. Therefore, in pediatric patients, the diagnosis must rely heavily on clinical and laboratory factors, and exclusion of secondary disorders to make an accurate diagnosis of MPN. This review focuses on the clinical presentation, diagnostic work up, differential diagnosis, treatment and prognosis of the classical BCR-ABL-negative MPNs (PV, ET and PMF) in children and highlights key differences to the adult diseases. Particular attention will be given to pediatric PMF, as it is the only disorder of this group that is observed in infants and young children, and in many ways appears to be a unique entity compared to adult PMF.

CALR mutation screening in pediatric primary myelofibrosis

BACKGROUND

Primary myelofibrosis (PMF) is quite rare in children. Mutations of JAK2(V617F) or MPL(W515K/L) were absent in pediatric patients with PMF according to previous studies. Recently, mutations in calreticulin (CALR) were described in adult patients with JAK2/MPL-unmutated PMF. Our study aimed to analyze the clinical and genetic features of Chinese pediatric patients with PMF.

PROCEDURES

We retrospectively investigated 14 pediatric patients diagnosed as PMF according to WHO 2008 criteria. Direct sequencing was performed for the existence of genetic alterations in JAK2, MPL, TET2, CBL, ASXL1, IDH1, IDH2, SRSF2, EZH2, DNMT3A and CALR.

RESULTS

In our cohort, all patients had anemia, three patients (21%) had splenomegaly, six patients (43%) had micromegakaryocytes at time of diagnosis. No patient had spontaneous remission and six patients (43%) transformed to acute myelocytic leukemia. In nine patients with evaluable cytogenetic information, three subjects (33%) had abnormal karyotypes. The median survival from time of diagnosis was 28 months. Seven patients (50%) had type 2 mutations of CALR. No patient had mutations in the other candidate genes. There was no statistical differences in age, gender, hemoglobin, WBC, neutrophil and platelet counts, percentage of circulating blast, overall survival and leukemia transformation between patients with and without CALR mutation.

CONCLUSION

Our study documented that Chinese pediatric patients with PMF in our cohort had its own clinical characteristics and poor outcome. CALR mutations were detected in 50% of our pediatric patients with PMF. Based on our study, CALR mutations screening could be used as molecular marker for diagnosis of pediatric patients with PMF.

Allogeneic hematopoietic stem cell transplantation for infants with idiopathic myelofibrosis

IMF is a rare disease in children that can present during infancy and has a protracted course. The only known curative approach for this disease in adult patients is allogeneic HSCT. There are very few reports describing the long-term outcome of young children following stem cell transplantation for IMF. We report on eight patients less than two yr of age with IMF that did not resolve with supportive care measures. All patients underwent myeloablative conditioning regimen with busulfan and cyclophosphamide ± ATG followed by HSCT from matched related (n = 6) or unrelated donor (n = 2). All patients achieved neutrophil and platelet engraftment. Four patients had grade II-III acute GVHD, and chronic GVHD developed in five patients (three mild and two severe). At a median follow-up of eight and a half yr (0.7-9), all patients are alive with complete resolution of their hematologic manifestations. At the last follow-up, all patients had normal endocrine function except for one patient who developed hypothyroidism. To date, this is the largest cohort of young children with IMF treated successfully with HSCT, with the longest duration of follow-up. In conclusion, our study showed that HSCT is a curative option for infants with IMF.

Idiopathic myelofibrosis in children: primary myelofibrosis, essential thrombocythemia, or transient process?

We report 3 pediatric cases of primary/idiopathic myelofibrosis (PMF/IMF). Two cases exhibited clinical courses not typically observed in adult patients in whom this process is much more common. One of these cases exhibited spontaneous clinical and bone marrow resolution, whereas the other case achieved near resolution of myelofibrosis in response to cytoreductive therapy alone. However, the third case of IMF that met diagnostic criteria for essential thrombocythemia with a JAK2V617F mutation had central venous thrombosis that resulted in blindness. PMF/IMF, a rare finding in children, does not seem to portend the same level of risk as seen in adults with the same process, thus less aggressive management may be appropriate. However, delayed diagnosis of mutation-associated PMF or essential thrombocythemia can lead to devastating consequences. We review the literature and discuss the complexities surrounding diagnosis, risk stratification, and management of pediatric PMF/IMF.

Stem cell transplantation in primary myelofibrosis of childhood

Fewer than 40 cases of primary myelofibrosis have been reported in children; hematopoietic stem cell transplantation is the only available curative therapy for this disease. Here, we describe the case of a female infant diagnosed with primary myelofibrosis at the age of 6 months; she underwent successful matched unrelated bone marrow transplantation with complete resolution of disease. We discuss some unique characteristics of primary myelofibrosis in children and review outcome data for children with this disease.

Allogeneic cord hematopoietic stem cell transplantation in an infant with primary myelofibrosis

Primary myelofibrosis (PMF) is rare in children. An allogeneic hematopoietic stem cell transplantation (HSCT) is the only known curative therapy for severe cases. Here, we report the case of a female infant with PMF treated with allogeneic HSCT using an unrelated cord blood unit. She had successful reversal of her disease, but experienced complications related to transplant. This is the seventh reported case of HSCT for PMF in children, and the second using umbilical cord blood. We conclude that cord HSCT is a useful curative treatment option in children with PMF, but that efforts must be taken to reduce complications.

Clinical, histopathologic, and genetic features of pediatric primary myelofibrosis--an entity different from adults

Primary myelofibrosis is a chronic myeloproliferative neoplasm characterized by cytopenias, leukoerythroblastosis, extramedullary hematopoiesis, hepatosplenomegaly and bone marrow fibrosis. Primary myelofibrosis is a rare disorder in adults; children are even less commonly affected by this entity, with the largest pediatric case series reporting on three patients. Most literature suggests spontaneous resolution of myelofibrosis without long term complications in the majority of affected children. We describe the clinical, pathologic, and molecular characteristics and outcomes of nineteen children with primary myelofibrosis treated in our center from 1984 to 2011. Most patients had cytopenia significant enough to require supportive therapy. No child developed malignant transformation and only five of the 19 children (26%) had spontaneous resolution of disease. Sequence analyses for JAK2V617F and MPLW515L mutations were performed on bone marrow samples from 17 and six patients, respectively, and the results were negative. In conclusion, analysis of this large series of pediatric patients with primary myelofibrosis demonstrates distinct clinical, hematologic, bone marrow, and molecular features from adult patients.

Myelofibrosis in children: experience at a single tertiary care center in India

The authors describe 10 cases of myelofibrosis diagnosed and managed at their center over 16 years. There were 2 and 8 cases, respectively, of primary and secondary myelofibrosis. All patients presented with fever, pallor, hepatosplenomegaly, and/or lymphadenopathy. Hodgkin's lymphoma (n = 4), neuroblastoma (n = 1), thrombasthenic thrombopathy (n = 1), and retroperitoneal-mass (n = 1) were causal in 7 patients, whereas the diagnosis could not be established in a sole case of secondary myelofibrosis. Patients were managed with chemotherapy and appropriate care. However, outcome was poor. The authors emphasize variable clinical-laboratory spectrum of myelofibrosis, highlight management concerns, and demonstrate that prognosis/outcome depends upon appropriate management of the underlying condition.

Transient myelofibrosis with autoimmune pancytopenia: a case report

INTRODUCTION

Myelofibrosis associated with myelodysplasia is thought to herald poor prognosis in myelodysplastic syndrome (MDS).

CASE REPORT

A 7-month-old boy presented with fever (39 degrees C), pancytopenia, and slight hepatosplenomegaly (3 and 2 cm, respectively). Bone marrow showed hypercellularity, hyperplasia of erythroblasts, and also myelofibrosis. IgG was 1,136 mg/dL, IgA was 131 mg/dL, and IgM was 89 mg/dL. Antinuclear and antineutrophil antibodies, red-blood-cell-associated IgG, antiplatelet antibodies, and Coombs test were positive. Karyotype was 46XY. No viral cause was evidenced. Mild myelodysplasia was revealed two months later, but was insufficient to support a diagnosis of MDS. The boy was treated with transfusion of packed cells, prednisolone 2 mg/kg/day for 3 weeks associated with intravenous gammaglobulin 400 mg/kg/day for 5 days. Direct Coombs remained positive 1 month after treatment for 5 months, myelofibrosis persisted for 3 months, and neutropenia for 21 months. After 3-year follow-up, hematological data were normal without any therapeutic intervention.

CONCLUSION

Myelofibrosis associated with mild myelodysplasia and pancytopenia can have a benign evolution in infants and young children.

Unrelated stem cell transplant for infantile idiopathic myelofibrosis

Idiopathic myelofibrosis (IMF) is a rare disease in children that can present during infancy and have a protracted course. The only known curative approach for this disease in adult patients is allogeneic stem cell transplant. We present two cases of IMF during infancy that did not resolve with supportive care measures. Both patients underwent unrelated stem cell transplant with complete resolution of their hematologic manifestations and resolution of the bone marrow fibrosis.

Life expectancy and prognostic factors in the classic BCR/ABL-negative myeloproliferative disorders

Among the 'classic' BCR/ABL-negative chronic myeloproliferative disorders, primary myelofibrosis (PMF) is associated with a substantial life-expectancy reduction. In this disease, initial haemoglobin level is the most important prognostic factor, whereas age, constitutional symptoms, low or high leukocyte counts, blood blast cells and cytogenetic abnormalities are also of value. Several prognostic systems have been proposed to identify subgroups of patients with a different risk, which is especially important in younger individuals, who may benefit from therapies with curative potential. Essential thrombocythaemia (ET) affects the patients' quality of life more than the survival, due to the high occurrence of thrombosis, whereas polycythaemia vera (PV) has a substantial morbidity derived from thrombosis but also a certain reduction in life expectancy. Therefore, in the latter disorders, prognostic studies have focused primarily on prediction of the thrombosis, with age and a previous history of thrombosis being the main prognostic factors of such complication. The importance of higher leukocyte counts in thrombosis development has been recently pointed out in ET and PV, where a role for mutated JAK2 allele burden has also been noted. With regard to PMF, the possible association of the mutation with shorter survival and higher acute transformation rate is currently being evaluated.

Hereditary and familial syndromes of bone and blood. Genetic pathways, diagnostic pitfalls

Numerous metabolic disorders, teratogenic agents, and in utero infections lead to congenital bone disease and malformation. This review focuses on hereditary and familial disorders of bone with particular emphasis on impaired hematopoiesis, myelofibrosis, pathologic fractures, and dysmorphology of the forearm and craniofacial structures. The severity of bone disease and marrow dysfunction of any given disorder may vary considerably from one affected individual to the next, and intrapersonal variability over time may be substantial as well. Both can impart difficulty to the appropriate evaluation and delay the correct diagnosis. Many of these disorders are phenotypically quite similar but require very different therapeutic intervention.

New insights into the pathogenesis and drug treatment of myelofibrosis

PURPOSE OF REVIEW

Myelofibrosis with myeloid metaplasia was first described in 1879, classified as a myeloproliferative disorder in 1951, and characterized as a clonal stem cell disorder in 1978. Despite the passing of time, the molecular basis of the disease has remained elusive although substantial progress has been made regarding the pathogenesis of the associated bone marrow stromal reaction. Advances have also been meager in terms of treatment for disease complications, including anemia, splenomegaly, and leukemic transformation.

RECENT FINDINGS

At the molecular level, a JAK2 tyrosine kinase mutation (JAK2) has recently been described in a spectrum of myeloproliferative disorders including myelofibrosis with myeloid metaplasia with the reported mutational frequency ranging from 35% to 57% with 9-29% homozygosity. To date, the presence of JAK2 in myelofibrosis with myeloid metaplasia has not been shown to have prognostic relevance. Other recent observations of potential pathogenetic relevance in this disease include the description of a highly specific chromosomal translocation {der(6)t(1;6)(q23;p21)}, the demonstration of an epigenetic downregulation of the retinoic acid receptor-beta2 expression in CD34 cells, and the direct implication of transforming growth factor-beta1 in thrombopoietin-driven experimental myelofibrosis in mice. From a therapeutic standpoint, benefit to a subset of patients has been demonstrated for both allogeneic stem cell transplantation and novel drugs, including thalidomide and lenalidomide.

SUMMARY

Recent advances in the pathogenesis of myelofibrosis with myeloid metaplasia are expected to facilitate the development of molecularly targeted therapy. In the mean time, current management strategies include observation, participation in experimental drug therapy, and allogeneic stem cell transplantation for low-risk, intermediate-risk, and high-risk disease, respectively.

Chronic idiopathic myelofibrosis: clinicopathologic features, pathogenesis, and prognosis

CONTEXT

Chronic idiopathic myelofibrosis (CIMF) is a clonal myeloproliferative disease characterized by panmyelosis with intact maturation, progressive bone marrow fibrosis, and multiorgan extramedullary hematopoiesis.

OBJECTIVE

This review article aims to summarize the recent updates regarding the clinicopathologic features, molecular pathogenesis, cytogenetic abnormalities, diagnostic criteria, new diagnostic ancillary tests, and prognostic factors of CIMF.

DATA SOURCES

Important relevant articles indexed in PubMed/MEDLINE (National Library of Medicine) through the end of 2005 and referenced medical texts.

CONCLUSIONS

Because CIMF has a variety of clinical presentations, diagnosis may be challenging; the prefibrotic stage of CIMF has always been a challenging disease for pathologists to diagnose accurately. The recently proposed European Clinical and Pathological criteria can be helpful in the diagnosis of CIMF, especially in its prefibrotic stage. The enumeration of CD34-positive cells in the peripheral blood and the presence of circulating endothelial progenitor cells are the new important ancillary tests for the diagnosis of a small subset of patients with CIMF with atypical presentation. The recent discovery of the new mutation affecting the Janus tyrosine kinase 2 (JAK2V617F), more frequently observed in patients with polycythemia vera, is seen in approximately 35% to 57% of patients with CIMF. This mutation can serve as another diagnostic tool. Important factors affecting prognosis in CIMF are anemia, age of the patient, white blood cell count, degree of fibrosis, and number of blasts in the peripheral blood.

Idiopathic myelofibrosis with generalized periostitis in a 4-year-old girl

Idiopathic myelofibrosis, a chronic myeloproliferative disorder of unknown origin, is characterized by splenomegaly, extramedullary hematopoiesis, leukoerythroblastosis, teardrop erythrocytes, and myelofibrosis. It is a rare disorder in childhood. The authors describe a 4-year-old girl with features consistent with idiopathic myelofibrosis, who also had generalized solid laminated periosteal reaction involving all long bones. The presence of thrombocytopenia at the onset and lack of leukocytosis were in contrast to the reported features seen in children. Recent case reports describe a relatively indolent course in children. Spontaneous remissions have also been described in pediatric cases. The fulminant course of this patient without any features of malignant transformation was noteworthy in this regard.

A basic classification and a comprehensive examination of pediatric myeloproliferative syndromes

Myeloproliferative syndromes (MPSs) are clonal stem cell disorders resulting in excessive proliferation of one or more cell lineages. Since MPSs in children occur much less commonly than adults, one can argue that the biology and the categories of the various pediatric MPSs seem to be different from adults. Furthermore, confusion exists between pediatric MPS and other overlapping conditions, such as myelodysplastic syndrome. The authors' objectives were to develop a classification system with a list of disorders relevant to children and to characterize pediatric cases of MPS that were devised according to this classification. Based on the predominant proliferating cell lineage, the authors established a classification system for childhood MPS. Primary MPS was classified into granulocytic proliferation--chronic myelogenous leukemia (CML); monocytic--juvenile myelomonocytic leukemia (JMML); megakaryocytic--essential thrombocythemia (ET), familial thrombocytosis, transient myeloproliferative disorder of Down syndrome (TMD); erythrocytic--polycythemia vera, familial erythrocytosis; fibroblastic--idiopathic myelofibrosis (IMF); eosinophilic--idiopathic hypereosinophilic syndrome (IHES); and mast cells--mastocytosis. Secondary MPS was classified as non-clonal proliferation (eg, infections, drugs, toxins, autoimmune, non-hematologic neoplasm, and trauma), and these were excluded from the study. Next, the classification system was applied to the patient population at the authors' institution. One hundred two cases with primary MPS were identified between 1970 and 2001. Patients were evaluated for clinical manifestations, blood and bone marrow parameters, cytogenetics, and survival following different treatment modalities. Significant proportions of cases of childhood MPS (60%) were unique to the pediatric population and not seen in adults. The most common disorders were JMML (n = 31), TMD of Down syndrome (n = 30), and CML (n = 30); the other disorders were rare: four cases of ET, two of IMF, two of IHES, two of mastocytosis, and one primary erythrocytosis. In contrast to adults, MPS in children is more frequently treated with hematopoietic stem cell transplantation (HSCT), the only available curative option for most of these diseases. HSCT was particularly successful in the more recent cases due to more advanced techniques for HSCT. The authors found that all the cases could be easily classified. MPS in children is different from adult-type MPS in terms of biology, categories, classification, and prognosis.

Zoledronate-induced remission of acute panmyelosis with myelofibrosis

Acute panmyelosis with myelofibrosis is a rare and aggressive form of acute myeloid leukemia. We describe a new case with a huge proliferation of megakaryocytes, blast cells and reticulin fibers. The patient was treated with zoledronate, a third-generation bisphosphonate, and a gradual recovery from pancytopenia was observed. A new bone marrow biopsy performed 4 months later showed a surprising disappearance of the leukemic infiltration. Ten months after the diagnosis, the patient is still in healthy condition. This may support the recently described anti-tumor activity of zoledronate.

Myelofibrosis with myeloid metaplasia: new developments in pathogenesis and treatment

Myeloid metaplasia with myelofibrosis (MMM) is a chronic myeloproliferative disorder (CMPD) characterized by progressive anemia, massive splenomegaly, both hepatosplenic and non-hepatosplenic extramedullary hematopoiesis (EMH), a leukoerythroblastic blood smear, circulating progenitor cells, and marked bone marrow stromal reaction including collagen fibrosis, osteosclerosis and angiogenesis. The overall median survival is 5 years although it might range from 2 to 15 years depending on the presence or absence of clinically defined prognostic factors. Death is often due to leukemic transformation, portal hypertension or infection. In addition to shortened survival, quality of life is often affected by frequent red blood cell transfusions, profound constitutional symptoms, and cachexia. Drug therapy and autologous hematopoietic stem cell transplantation (HSCT) are of only palliative value and have not been shown to improve survival. The role of allogeneic HSCT, both myeloablative and non-myeloablative, is actively being investigated. Both splenectomy and radiation therapy have defined therapeutic roles to control EMH-associated symptoms. Analysis of the molecular biology of the disease is underway with the aid of animal models leading to the identification of novel therapeutic targets. Among the novel agents tested, thalidomide seems the most promising although newer agents are on the horizon.

Pulmonary hypertension complicating bone marrow transplantation for idiopathic myelofibrosis

Idiopathic myelofibrosis is a rare hematologic disorder that is occasionally associated with pulmonary hypertension and has been cured with bone marrow transplantation (BMT). Most cases occur in older adults, but children with similar clinical and pathologic findings have been described. The authors describe a critically ill male infant with idiopathic myelofibrosis and subtle findings suggestive of pulmonary hypertension who was treated with BMT after failing to respond to chemotherapy. After BMT, the patient's clinical course improved in all respects, but he ultimately died of progressive pulmonary hypertension.

The forgotten myeloproliferative disorder: myeloid metaplasia

Myelofibrosis with myeloid metaplasia is a hematologic disorder currently classified with polycythemia vera and essential thrombocythemia as a chronic myeloproliferative disease. The median age at diagnosis is 60 years, and more than 90% of patients are diagnosed after age 40 years. Clinical manifestations include massive splenomegaly, progressive anemia, profound constitutional symptoms, and extramedullary hematopoiesis. The diagnosis is confirmed by bone marrow examination after other causes of myelofibrosis are ruled out. Median survival is 5 years and causes of death include leukemic transformation. Prognosis is adversely affected by the presence of anemia (hemoglobin <10 g/dl), leukopenia or leukocytosis (white blood cells >30,000/ micro l), circulating blasts, and hypercatabolic symptoms. Conventional treatment is palliative and does not improve survival. In this regard, androgen preparations, corticosteroids, and erythropoietin are useful for the treatment of disease-associated anemia. Symptomatic splenomegaly is best managed by cytoreductive therapy or surgical removal. Radiation therapy is most useful in the treatment of nonhepatosplenic extramedullary hematopoiesis. New treatment approaches include the use of thalidomide alone or in combination with prednisone and hematopoietic stem cell transplantation.

Myelofibrosis with myeloid metaplasia in adult individuals 30 years old or younger: presenting features, evolution and survival

Myelofibrosis with myeloid metaplasia (MMM) usually affects older people and is associated with a median survival of 3.5-5 yr. Survival of MMM patients 55 yr old or younger is longer, but there is no information on the youngest subset. The presenting features, evolution and survival were analyzed in 9 patients with MMM aged 30 yr or less, representing 2.8% of two series including 323 cases. Age ranged from 17 to 30 yr; 3 patients were males and 6 females. Five patients were asymptomatic and none had constitutional symptoms. Anemia was observed in 4 patients, being severe in only one. The WBC count was normal in 7 patients and 2 had mild leukocytosis; moderate thrombocytosis was observed in 7 patients. No patient showed blood blast cells or bone marrow cytogenetic abnormalities. With a median follow-up of 6.8 (range 0.8-28) yr, 2 patients died 10.7 and 9.9 yr from diagnosis, one from complications of bone marrow transplantation performed after progression of the disease and the other from gastrointestinal bleeding secondary to portal hypertension. Among remaining patients, one developed Budd-Chiari syndrome, another was lost to follow-up at 3 yr, and 5 remain asymptomatic and currently without treatment (one had been splenectomized at diagnosis). These results indicate that in most young adults with MMM the disease presents without adverse prognostic factors and may remain stable for years, which may be of interest when considering the treatment of such patients.