Primary MF is considered a chronic myeloproliferative disorder and is characterized by variable degrees of cytopenia, cytosis, bone marrow fibrosis, a leukoerythroblastic blood picture, and extramedullary hematopoiesis, which can result in hepatosplenomegaly (Cervantes et al, 2009). MF is a heterogeneous disease in that MF is an indolent disease in some patients, who may survive for decades, to an aggressive disease in others, with disabling symptoms, lowered quality of life and in some cases survival of less than a year (McLornan et al, 2012). MF can be either primary or secondary, and can develop in patients with polycythemia vera or essential thrombocythemia. The median age is in the seventh decade and approximately 70% of patients are positive for the Janus2 kinase mutation (Ballen, 2012).
There have been no available conventional drug therapies for MF which have been shown to prolong survival. Palliative agents include erythropoietin, androgens, immunomodulatory agents, interferons, cytoreductive therapies and non-pharmacologic approaches. The non-pharmacologic approaches include blood transfusion, splenic irradiation, and splenectomy. Allogeneic hematopoietic stem cell transplantation (SCT) is considered to be the only potentially curative therapy for MF (McLornan et al, 2012).
The American Society for Blood and Marrow Transplantation Guideline on the role of cytotoxic therapy with hematopoietic stem cell transplantation in the therapy of myelodysplastic syndrome states that” early SCT is recommended for patients with an International Prognostic Scoring System (IPSS) score of intermediate (INT) -2 (considered high risk) at diagnosis who have a suitable donor and meet the transplant center’s eligibility criteria, and for selected patients at low risk (IPSS score of INT-1) at diagnosis who have poor prognostic features not included in the IPSS (e.g. older age, refractory cytopenias) (Oliansky et al, 2009). The IPSS estimates survival from the time of diagnosis based on five risk factors : age > 65 years, hemoglobin < 100 g/l, leukocyte count > 25 x 109/l, circulating blasts ≥ 1%, and the presence of constitutional symptoms. Patients are then classified as low risk (score = 0), intermediate risk-1 (score = 1), intermediate risk-2 (score = 2), and high risk (score ≥ 2) (McLornan et al, 2012).
Cervantes et al (2009) studied 1054 patients at 7 centers who were diagnosed with primary MF. The purpose of this retrospective study was to develop a highly discriminative prognostic system. Variables selected for prognostic assessment were those previously shown to be of prognostic value in primary MF along with variables considered to be either clinically meaningful or potential confounders. Analysis using Cox proportional hazards modeling revealed identified age greater than 65 years, presence of constitutional symptoms, hemoglobin level less than 10 g/dL, leukocyte count greater than 25 x 109/L, and circulating blast cells 1% or greater as predictors of shortened survival. Overall median survival was 69 months (95% confidence interval: 61-71). Four risk groups with no overlap in their survival curves were identified, including 0 (low risk), 1 (intermediate risk-1), 2 (intermediate risk-2), or greater than or equal to 3 (high risk), with respective median survivals of 135, 95, 48, and 27 months (p < 0.001). Additionally, in 409 patients with assessable metaphases, cytogenetic abnormalities were associated with shorter survival, but their independent contribution to prognosis was restricted to patients in the intermediate-risk groups. JAK2V617F did not cluster with a specific risk group or affect survival.
A prospective multicenter trial was conducted in 103 patients with various forms of MF to determine the efficacy of a busulfan (10 mg/kg) fludarabine (180 based reduced-intensity conditioning regimen followed by allogeneic stem cell transplantation from related (n = 33) or unrelated donors (n = 70). Cumulative incidence of nonrelapse mortality at 1 year was 16% and was significantly lower for patients with a completely matched donor. The estimated 5-year event-free survival was 51% and 68%, respectively (Kroger et al, 2009).
Tefferi et al (2011a) noted that “current drug therapy in primary MF is neither curative or essential for survival. Similarly, it is not clear if the application of allogeneic SCT, with its attendant risk of death or chronic morbidity from graft-versus-host disease, has had a favorable or unfavorable net effect. Therefore, one must first determine whether a particular patient needs any form of therapy at all and , if so, carefully select the treatment strategy with the best chance of inducing disease control without compromising life expectancy.” Tefferi et al (2011b) reported that the presence of fibrosis, JAK2/MPL mutation or +9/13q- cytogenic abnormality is supportive but not essential for diagnosis, and that diagnosis is based on bone marrow morphology. The authors state that observation alone is adequate for asymptomatic low/intermediate-1 risk disease; allogeneic SCT or experimental drug therapy is reasonable for symptomatic intermediate-1 risk disease.
Alchalby et al (2012) evaluated 150 homogeneously treated MF patients who underwent reduced-intensity allogeneic SCT and developed a risk score for overall survival. The authors’ prognostic scoring system compared to the Lille scoring system and correlated significantly with overall survival but discriminated poorly between the intermediate and high-risk groups. The authors concluded that a simple model which includes age, JAK2 V617F-status, and constitutional symptoms can clearly separate distinct risk groups. The authors further noted that such a model can be used in addition to the Lille model to predict overall survival after reduced-intensity allogeneic SCT.
Scott et al (2012) conducted a study to evaluate a Dynamic International Prognostic Scoring System (DIPSS) risk categorization. They evaluated the DIPSS in 170 MF patients aged 12 to 78 years who received SCT from related (n = 86) or unrelated (n = 84) donors. The investigators determined that 21 patients had low-risk disease, 48 had intermediate-1, 50 had intermediate-2, and 51 had high-risk disease. Additionally, they reported five-year incidence of relapse, relapse-free survival, overall survival, and nonrelapse mortality for all patients were 10%, 57%, 57%, and 34%, respectively. They concluded that SCT was curative for a large proportion of patients with MF, and post-SCT success was dependent on pre-SCT DIPSS classification.
In a recent review of allogeneic stem cell transplantation for MF, McLornan et al (2012) concluded that transplant-eligible MF patients with intermediate-2 and high-risk disease should be considered for SCT. Additionally, patients with transfusion dependency or an unfavorable karyotype should also be considered for SCT. The authors suggested a myeloablative conditioned approach in those greater than 45 years of age, and acknowledged that some patients between 45 and 50 years of age with low HCT-CI scores may well also be suitable for a myeloablative conditioned SCT. They further suggested that a reduced-intensity conditioning regimen be considered for those over the age of 45 years and that patients older than 65 years should not be definitively excluded from potential SCT on age criteria alone, but rather that “a frank discussion with the patient regarding the association of older age and, in general, an adverse post-SCT outcome should occur in addition to a detailed risk assessment."