Primary Myelofibrosis Medical Services in China

Primary Myelofibrosis (PMF) is a rare, chronic Philadelphia chromosome-negative myeloproliferative neoplasm characterized by clonal proliferation of abnormal hematopoietic stem cells, progressive bone marrow fibrosis, extramedullary hematopoiesis (especially in the spleen and liver), and cytopenias. Unlike secondary myelofibrosis—which arises from other underlying conditions such as polycythemia vera or essential thrombocythemia—PMF originates de novo, with hallmark driver mutations in JAK2 (≈50–60%), CALR (≈25–35%), or MPL (≈5–10%). These mutations constitutively activate the JAK-STAT signaling pathway, leading to dysregulated cytokine production, aberrant megakaryocyte differentiation, and release of fibrogenic growth factors (e.g., TGF-β, PDGF) that stimulate reticulin and collagen deposition by bone marrow stromal cells. Over time, this fibrotic remodeling impairs normal hematopoiesis, resulting in anemia, thrombocytopenia, leukoerythroblastic peripheral blood smear, splenomegaly, and constitutional symptoms including fatigue, night sweats, weight loss, fever, and early satiety. Epidemiologically, PMF affects approximately 0.5–1.5 per 100,000 individuals annually, with median age at diagnosis around 65 years; it is slightly more common in males and shows no strong ethnic predilection. Risk factors include advancing age, presence of high-risk somatic mutations (e.g., ASXL1, SRSF2, IDH1/2, U2AF1), unfavorable karyotype (e.g., complex or monosomal abnormalities), severe anemia (hemoglobin <10 g/dL), leukocytosis >25 × 10⁹/L, circulating blasts ≥1%, and transfusion dependence. Quality of life is profoundly impacted: patients frequently experience debilitating fatigue, pain from massive splenomegaly, pruritus, cachexia, and anxiety related to disease progression and risk of transformation to acute myeloid leukemia (AML)—which occurs in 10–20% of cases over 10 years. Symptom burden correlates poorly with traditional lab parameters, underscoring the importance of patient-reported outcomes in clinical assessment. Management focuses on risk-adapted strategies: low-risk patients may require only observation or supportive care (e.g., erythropoiesis-stimulating agents, transfusions, hydroxyurea for splenomegaly control), while intermediate- and high-risk patients benefit from JAK inhibitors (ruxolitinib, fedratinib, pacritinib) to alleviate symptoms and reduce splenomegaly. Allogeneic hematopoietic stem cell transplantation remains the only potentially curative option—but is limited to fit patients under age 70 with suitable donors due to significant morbidity and mortality. Ongoing research explores combination therapies, novel antifibrotic agents, and immunomodulatory approaches to modify disease biology.

Primary myelofibrosis (PMF) is a rare, clonal hematopoietic stem cell disorder classified under the Philadelphia chromosome–negative myeloproliferative neoplasms (MPNs). It is characterized by progressive bone marrow fibrosis, extramedullary hematopoiesis (particularly in the spleen and liver), ineffective hematopoiesis, and a variable clinical course ranging from indolent to aggressive with risk of transformation to acute myeloid leukemia (AML). Unlike secondary myelofibrosis—which arises as a consequence of other hematologic malignancies, autoimmune disorders, or chronic infections—PMF originates de novo without an identifiable antecedent condition.

The fundamental cause of PMF is acquired somatic mutations in hematopoietic stem or progenitor cells, leading to constitutive activation of the JAK–STAT signaling pathway. The most prevalent driver mutation is JAK2 V617F, present in approximately 55–60% of patients. This gain-of-function mutation results in ligand-independent phosphorylation of JAK2, perpetuating cytokine-independent proliferation and survival signals. Additional driver mutations include CALR (calreticulin) exon 9 insertions/deletions, found in 25–30% of JAK2-negative cases, and MPL (myeloproliferative leukemia virus oncogene) exon 10 mutations (e.g., W515K/L), occurring in 5–8% of patients. These mutations converge on hyperactivation of JAK–STAT signaling, promoting aberrant megakaryocyte proliferation, dysplastic maturation, and release of pro-fibrotic cytokines—including TGF-β, PDGF, FGF, and TNF-α—which stimulate bone marrow stromal cells (particularly fibroblasts and mesenchymal stromal cells) to deposit excessive reticulin and collagen fibers, culminating in marrow fibrosis.

While these genetic lesions are necessary for clonal dominance, they are insufficient alone to explain disease heterogeneity, progression, or phenotypic variability. Co-occurring somatic mutations in epigenetic regulators (e.g., ASXL1, EZH2, TET2, IDH1/2, DNMT3A), spliceosome components (SF3B1, SRSF2, U2AF1), and transcription factors (RUNX1) significantly influence prognosis, risk of leukemic transformation, and therapeutic response. For instance, ASXL1 mutations are independently associated with shortened overall survival and accelerated fibrosis progression; SRSF2 mutations correlate with higher risk of AML transformation and cytopenias.

No definitive environmental triggers have been established for PMF. Unlike some hematologic malignancies, there is no robust epidemiologic evidence linking PMF to ionizing radiation exposure, benzene, pesticides, or prior chemotherapy—though such exposures may contribute to genomic instability in predisposed individuals. Similarly, chronic inflammation or infection has not been causally implicated in PMF pathogenesis, distinguishing it from reactive or secondary myelofibrosis. However, inflammatory cytokine networks—fueled by mutant megakaryocytes and activated monocytes—create a self-perpetuating microenvironment that amplifies fibrosis and clonal selection.

Age is the strongest non-genetic risk factor: median age at diagnosis is 65–70 years, and incidence rises sharply after age 60. There is a modest male predominance (male-to-female ratio ~1.3:1), though biological mechanisms remain unclear. Family history is rarely contributory; germline predisposition syndromes (e.g., familial platelet disorder with propensity to myeloid malignancy linked to RUNX1 mutations) are exceedingly uncommon in PMF and do not account for population-level risk. Constitutional factors such as obesity or metabolic syndrome have not been validated as independent risk factors, though chronic low-grade inflammation in these conditions may theoretically modulate disease behavior.

Importantly, PMF is not inherited, nor is it contagious. It arises sporadically from post-zygotic somatic mutations. While certain polymorphisms in JAK2 (e.g., the JAK2 46/1 haplotype) confer increased susceptibility to acquiring the V617F mutation, they do not cause disease directly and are common in the general population. No occupational, geographic, dietary, or lifestyle factors have demonstrated reproducible association with PMF incidence in large cohort studies.

In summary, PMF is driven predominantly by acquired somatic mutations activating JAK–STAT signaling, with disease phenotype, tempo, and complications shaped by the constellation of co-mutations and the resulting inflammatory and fibrogenic bone marrow microenvironment. Age remains the principal demographic risk factor, while environmental and behavioral determinants appear negligible. Understanding this molecular architecture underpins risk stratification (e.g., MIPSS70+ version 2.0), prognostication, and targeted therapy—including JAK inhibitors (ruxolitinib, fedratinib, pacritinib) and emerging agents targeting mutant CALR or epigenetic modifiers.

Primary myelofibrosis (PMF) is a clonal hematopoietic stem cell disorder classified under the Philadelphia chromosome–negative myeloproliferative neoplasms (MPNs). It is characterized by progressive bone marrow fibrosis, extramedullary hematopoiesis (EMH), splenomegaly, and cytopenias despite a hypercellular or fibrotic marrow. Clinical presentation is highly heterogeneous, ranging from asymptomatic detection on routine blood tests to severe constitutional, hematologic, and organ-invasive manifestations.

Early symptoms are often nonspecific and insidious. Approximately 20–30% of patients are asymptomatic at diagnosis, identified incidentally via abnormal complete blood count (CBC) or imaging. When present, early manifestations include fatigue (reported in >70% of symptomatic patients), low-grade fever, night sweats, and unintentional weight loss (>10% body weight over six months)—collectively termed B symptoms per WHO criteria. Mild anemia-related symptoms such as exertional dyspnea, lightheadedness, or pallor may be attributed to other common conditions. Early thrombocytopenia or thrombocytosis may manifest as easy bruising, epistaxis, or prolonged bleeding after minor trauma—or conversely, as unexplained thrombotic events (e.g., deep vein thrombosis, transient ischemic attack), particularly in patients with JAK2 V617F mutation and elevated platelet counts (>1,000 × 10⁹/L). Some patients report early left upper quadrant discomfort due to subclinical splenomegaly, though palpable splenomegaly is typically absent at this stage.

Typical symptoms emerge as disease progresses and correlate with increasing marrow fibrosis, EMH, and cytokine-driven inflammation. Marked splenomegaly—often massive (>15 cm below costal margin)—is present in >80% of patients at diagnosis or during follow-up. Splenomegaly causes early satiety, postprandial abdominal discomfort, left shoulder pain (referred splenic infarction), and occasionally gastric compression leading to weight loss. Hepatomegaly occurs in ~40–50% due to hepatic EMH and may contribute to right upper quadrant pain or portal hypertension. Anemia becomes more pronounced (hemoglobin <10 g/dL in ~50% at diagnosis), resulting in progressive fatigue, exercise intolerance, tachycardia, and angina in patients with underlying cardiovascular disease. Thrombocytopenia (<100 × 10⁹/L) develops in ~30–40% and predisposes to mucocutaneous bleeding; conversely, thrombocytosis (>450 × 10⁹/L) persists in ~25% and increases thrombotic risk. Leukocytosis (>11 × 10⁹/L) with immature granulocytes (leukoerythroblastosis on peripheral smear) is characteristic and reflects EMH and marrow stress.

Accompanying symptoms reflect systemic inflammation and cytokine dysregulation. Elevated levels of IL-2Rα, TNF-α, TGF-β, and basic fibroblast growth factor drive constitutional symptoms and marrow stromal remodeling. Patients frequently report profound pruritus—often aquagenic—due to aberrant histamine and serotonin release. Gout may develop secondary to chronic cell turnover and hyperuricemia. Bone pain (particularly sternal or pelvic) arises from marrow expansion and osteosclerosis. Neuropsychiatric symptoms—including depression, anxiety, and cognitive fog—are increasingly recognized as integral components of MPN-related symptom burden, likely mediated by chronic inflammatory signaling and cytokine effects on the central nervous system.

Complications significantly impact morbidity and mortality. Acute myeloid leukemia (AML) transformation occurs in 10–20% of PMF patients over 10 years and portends dismal prognosis (median survival <6 months post-transformation). Portal hypertension and its sequelae—including esophageal varices, ascites, and hepatic encephalopathy—result from extensive hepatic EMH and sinusoidal obstruction. Splenic infarction or rupture necessitates urgent intervention. Pulmonary hypertension (due to pulmonary EMH or chronic hypoxia) and cardiac failure (from high-output state or amyloid deposition) are underrecognized but life-threatening. Infections are frequent due to functional neutrophil defects and immunosuppressive therapy. Thrombohemorrhagic diathesis—simultaneous risk of arterial/venous thrombosis and bleeding—is a hallmark complication driven by platelet dysfunction, endothelial activation, and procoagulant microparticles.

Diagnosis requires integration of clinical, morphologic, molecular, and cytogenetic data per WHO 2022 criteria. Essential diagnostic features include: (1) presence of megakaryocyte proliferation and atypia accompanied by reticulin and/or collagen fibrosis (grade ≥2/3); (2) exclusion of reactive myelofibrosis (e.g., autoimmune, infectious, metastatic causes); (3) demonstration of clonality—most commonly JAK2 V617F (55–65%), CALR exon 9 mutations (20–25%), or MPL W515K/L (5–10%); and (4) absence of BCR::ABL1 fusion. Supporting criteria include anemia not attributable to comorbidities, leukoerythroblastosis, increased serum lactate dehydrogenase (LDH), palpable splenomegaly, and JAK2/CALR/MPL mutation. Bone marrow biopsy remains the gold standard for assessing fibrosis grade (reticulin stain with silver impregnation) and megakaryocyte morphology. Next-generation sequencing panels evaluate additional somatic mutations (ASXL1, EZH2, SRSF2, IDH1/2, U2AF1) that inform prognostication (MIPSS70+ version 2.0). Cytogenetics (karyotype) identifies high-risk abnormalities (e.g., complex karyotype, +8, −7/7q−, i(17q)). Imaging includes abdominal ultrasound or MRI to quantify splenic/hepatic volume and assess for EMH; FDG-PET/CT may detect occult EMH sites.

Differential diagnosis is critical to avoid misclassification. Reactive (secondary) myelofibrosis must be excluded—causes include chronic infections (e.g., tuberculosis, HIV), autoimmune disorders (e.g., systemic lupus erythematosus, scleroderma), lymphoproliferative malignancies (e.g., hairy cell leukemia, Hodgkin lymphoma), metastatic carcinoma, and toxic exposures (e.g., benzene). Other MPNs—particularly post-polycythemia vera or post-essential thrombocythemia myelofibrosis—require careful historical review and documentation of prior MPN diagnosis. Chronic myeloid leukemia (CML) mimics PMF with splenomegaly and leukoerythroblastosis but is distinguished by BCR::ABL1 positivity. Myelodysplastic/myeloproliferative neoplasm (MDS/MPN), especially chronic myelomonocytic leukemia (CMML), may show overlapping features but lacks prominent fibrosis and displays monocytosis (>1 × 10⁹/L) and dysplasia. Acute megakaryoblastic leukemia (AMKL) presents with marrow fibrosis and circulating blasts but demonstrates ≥20% blasts and distinct immunophenotype (CD41+, CD61+). Finally, inherited bone marrow failure syndromes (e.g., Fanconi anemia) and idiopathic aplastic anemia with reticulin hyperplasia must be considered in younger patients. Accurate differentiation hinges on comprehensive clinical evaluation, rigorous morphologic assessment, and judicious use of molecular diagnostics.

Primary myelofibrosis (PMF) is a rare, clonal myeloproliferative neoplasm characterized by bone marrow fibrosis, extramedullary hematopoiesis (predominantly in the spleen and liver), progressive cytopenias, constitutional symptoms, and risk of leukemic transformation. Management is individualized based on disease risk stratification (e.g., DIPSS-plus: Dynamic International Prognostic Scoring System–plus), symptom burden, age, comorbidities, and transplant eligibility. Treatment goals include alleviating symptoms, correcting cytopenias, reducing splenomegaly, delaying disease progression, and improving overall survival—particularly through allogeneic hematopoietic stem cell transplantation (allo-HSCT) in eligible patients.

Conservative treatment forms the cornerstone for low- and intermediate-1–risk patients without significant symptoms or cytopenias. This includes regular clinical and laboratory monitoring (CBC, peripheral blood smear, LDH, uric acid, serum ferritin, and periodic bone marrow biopsy with cytogenetics and molecular profiling—including JAK2 V617F, CALR, and MPL mutations). Supportive care is essential: red blood cell transfusions for symptomatic anemia (with iron chelation therapy if ferritin exceeds 1,000 ng/mL after ≥30 units); platelet transfusions for severe thrombocytopenia with bleeding; and prophylactic anticoagulation in high-risk thrombotic settings (e.g., prior thrombosis, JAK2-mutated disease, or immobilization). Nutritional support, fatigue management, and psychosocial counseling are integral to maintaining quality of life. Splenic radiation may be considered for palliation of painful splenomegaly when pharmacologic options fail or are contraindicated, though effects are transient and carry risks of cytopenias and secondary malignancy.

Pharmacotherapy targets both disease biology and symptom control. Ruxolitinib—a first-generation JAK1/JAK2 inhibitor—is FDA- and NMPA-approved for intermediate- or high-risk PMF and has demonstrated durable reductions in spleen volume (≥35% in ~40% of patients at 24 weeks), improvement in constitutional symptoms (e.g., night sweats, weight loss, pruritus), and potential survival benefit versus best available therapy. Fedratinib and pacritinib are alternative JAK inhibitors approved for ruxolitinib-intolerant or thrombocytopenic patients (platelet count <50 × 10⁹/L), respectively. Novel agents under investigation include momelotinib (JAK1/2 and ACVR1 inhibitor, approved for anemia-associated PMF), navitoclax (BCL-2/BCL-xL inhibitor in combination with ruxolitinib), and pelabresib (a BET inhibitor showing synergistic activity in phase III trials). Immunomodulatory agents (e.g., thalidomide ± prednisone or lenalidomide ± prednisone) may improve anemia in select patients but carry significant toxicity (neuropathy, venous thromboembolism, myelosuppression). Hydroxyurea remains useful for controlling marked leukocytosis or thrombocytosis but lacks impact on fibrosis or survival. Interferon-alpha (pegylated formulations preferred) may induce molecular responses in early-stage disease but is limited by tolerability.

Surgical treatment is largely restricted to splenectomy in highly selected cases—typically for massive, symptomatic splenomegaly refractory to medical therapy, severe cytopenias due to hypersplenism, or portal hypertension complications. Preoperative optimization includes vaccination (pneumococcal, meningococcal, Haemophilus influenzae type B), platelet transfusion support, and bridging anticoagulation. Laparoscopic approaches are increasingly utilized in experienced centers to reduce morbidity. However, splenectomy carries substantial perioperative risks: bleeding (especially with platelet dysfunction), infection (overwhelming post-splenectomy infection), thrombosis (splanchnic vein thrombosis in up to 20%), and accelerated disease progression. It is generally avoided in high-risk patients or those with marked leukocytosis (>25 × 10⁹/L) or circulating blasts >1%. Allo-HSCT remains the only potentially curative modality and is recommended for fit patients ≤70 years with intermediate-2 or high-risk DIPSS-plus scores. Reduced-intensity conditioning regimens have expanded eligibility, with 5-year overall survival rates of 40–60% and progression-free survival of 35–50%. Outcomes depend heavily on donor match, disease burden pre-transplant, and center expertise.

China offers distinct advantages in PMF management. First, rapid access to novel therapeutics: ruxolitinib received NMPA approval in 2017 and is widely available through national reimbursement programs, significantly lowering out-of-pocket costs. Second, China hosts several world-class transplant centers (e.g., Peking University People’s Hospital, Institute of Hematology & Blood Diseases Hospital in Tianjin) performing >1,000 allo-HSCTs annually for myeloid malignancies, with robust infrastructure for HLA typing, graft-versus-host disease (GVHD) prophylaxis (including post-transplant cyclophosphamide), and supportive care. Third, integration of traditional Chinese medicine (TCM) as adjunctive therapy—under rigorous hematologic supervision—has shown promise in ameliorating fatigue, improving appetite, and stabilizing hemoglobin in observational studies, though randomized data remain limited. Fourth, centralized biobanking and genomic profiling initiatives (e.g., China Kadoorie Biobank, Shanghai Blood Center’s MPN registry) facilitate real-world evidence generation and clinical trial enrollment. Finally, multidisciplinary ‘MPN clinics’—staffed by hematologists, transplant physicians, radiologists, pathologists, and palliative care specialists—are increasingly standard in tier-3 hospitals, ensuring coordinated, guideline-concordant care.

Recovery and long-term management emphasize patient empowerment and proactive surveillance. Patients should maintain a symptom diary tracking fatigue, night sweats, abdominal discomfort, bleeding episodes, and medication side effects. Regular follow-up every 3–6 months includes CBC, comprehensive metabolic panel, LDH, and physical exam with spleen measurement. Annual bone marrow evaluation is advised for patients with worsening cytopenias, rising blast percentage, or new cytogenetic abnormalities. Lifestyle modifications include avoiding NSAIDs (due to bleeding risk), using sun protection (JAK inhibitors increase non-melanoma skin cancer risk), engaging in moderate aerobic activity to combat fatigue, and adhering strictly to vaccination schedules (including annual influenza and COVID-19 boosters). Genetic counseling is recommended for first-degree relatives given the low but measurable familial clustering. Psychosocial support—including peer networks facilitated by organizations like the China Myeloproliferative Neoplasm Alliance—is vital for coping with chronic illness uncertainty. Ultimately, optimal PMF care requires balancing disease-modifying interventions with personalized supportive strategies, continuous risk reassessment, and shared decision-making grounded in evolving evidence.