A Hidden Driver Mutation in Myeloproliferative Neoplasms: SH2B3 and Diagnostic Implications and Response to Ropeginterferon Alfa-2b

Introduction

Myeloproliferative neoplasms (MPNs) are clonal hematological malignancies characterized by uncontrolled production of one or more blood cell lines. ¹ The majority of MPNs are driven by activating mutations in JAK2, CALR, or MPL which lead to dysregulated activation of the JAK-STAT pathway. ² Identification of one of these mutations in the correct clinical setting helps establish the diagnosis. ¹ However, a minority of patients lack these classical driver mutations and are described as triple-negative MPNs, a subset whose diagnosis and therapeutic strategies remain poorly understood. ³

The increasing use of next-generation sequencing (NGS) panels in MPN diagnosis has allowed the recognition of additional mutations which may contribute to clonal expansion in the absence of classical driver mutations. ⁴ Notably, SH2B3, also known as LNK, is an adaptor protein that negatively regulates JAK-STAT signaling. ⁵ Loss-of-function mutations in SH2B3 can impair this regulatory function leading to uncontrolled pathway activation and myeloid production. ⁶ Emerging evidence reports that SH2B3 mutations occur in approximately 5–7% of triple-negative MPNs, revealing their potential role as a nonclassical driver mutation. ⁷ Despite this, SH2B3-mutated MPNs remain under-characterized and not well defined.

Interferon-based therapies have demonstrated disease-modifying abilities in MPNs leading to normalized hematopoietic function. ⁸ Ropeginterferon alfa-2b, a long-acting interferon formulation, is approved for the treatment of adult patients with polycythemia vera (PV) but its value in MPNs driven by nonclassical mutations, including SH2B3, is limited. ⁸ Here, we present a case of SH2B3-mutated, triple-negative MPN in an elderly patient who demonstrated a robust clinical and hematologic response to ropeginterferon alfa-2b, highlighting the importance of molecular evaluation outside of classical driver mutations and a potential therapeutic role of interferon-based therapy in this molecular subset.

Case Presentation

A 75-year-old Caucasian man with a past medical history of spinal stenosis with multiple cervical spine surgeries and a long-standing history of leukocytosis, erythrocytosis, and thrombocytosis presented to clinic for evaluation of persistent leukocytosis. He reported a prior diagnosis of MPN documented for over three years, for which he had received no treatment. He reported headache, generalized bone pain, and night sweats but denied significant weight loss or pruritus. He was active and independent in activities of daily living. Family history was notable for cancers of unknown type in his mother and another relative. Physical examination revealed no hepatosplenomegaly.

Laboratory evaluation revealed leukocytosis (WBC 10.23 × 10³/μL), erythrocytosis (Hct 48.9%) and thrombocytosis (PLT 438 × 10³/μL). Peripheral smear showed normocytic, normochromic erythrocytes, mild thrombocytosis with occasional hypogranular forms, and no circulating blasts. Bone marrow aspiration and biopsy revealed hypercellular marrow (approximately 90%), which is abnormal for a 75-year-old patient; there was trilineage hematopoiesis; however, megakaryocytes were abnormal (Figure 1). Factor VIII immunohistochemical staining confirmed megakaryocytic lineage and highlighted morphologic atypia and abnormal distribution, supporting a clonal myeloproliferative process (Figure 2). There was no increase in blasts, and we found mild reticulin fibrosis (WHO grade 1/3). Iron stores were decreased, and no ringed sideroblasts were observed. Flow cytometry showed no increase in blasts or abnormal B- or T-cell populations. Cytogenetics revealed 45,X with loss of the Y chromosome, consistent with prior studies, reflecting a persistent clonal hematopoietic population consistent with a chronic MPN.OPEN IN VIEWER

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Figure 2.

(A) Factor VIII immunohistochemical stain of the atypical megakaryocytes in the clot section on low power (100×). (B) High power (400×) showing megakaryocytes are stained brown with light blue nuclei. The staining pattern confirms megakaryocytic lineage and demonstrates morphologic atypia and clustering which is supportive of a chronic myeloproliferative neoplasm.

Targeted NGS identified a pathogenic SH2B3 c.1481C>G (p.Ser494*) nonsense mutation, present at a variant allele frequency of approximately 49%, predicted to truncate the C-terminal domain and enhance JAK-STAT signaling. No canonical driver mutations in JAK2, CALR, or MPL were detected.

Given his clinical presentation and workup, a diagnosis of SH2B3-mutated, triple-negative MPN was established. We recommended to treat him with hydroxyurea; however, the patient and his family were worried about potential side effects of this chemotherapy agent. The patient was initiated on ropeginterferon alfa-2b 100 mcg every 2 weeks. His symptoms started improving shortly after he began his treatment, and at 3-month follow-up, he had achieved a normalized hematologic profile (WBC 6.79 × 10³/μL, Hct 41.8% and PLT 360 × 10³/μL). He tolerated treatment well without any reported side effects and was continued on the same regimen with routine monitoring of labs. He has maintained his response for 6 months with resolution of his symptoms; he continues to have a complete hematologic response without the need for phlebotomy, and he remains fully active and working full time.

Discussion

Triple-negative myeloproliferative neoplasms (MPNs) lack the common driver mutations in JAK2, CALR, and MPL. ³ They represent a rare subset of MPNs; however, their true incidence is likely not well documented given that the routine NGS panels do not test for them. ⁹ The occurrence of noncanonical mutations in MPNs is challenging as their clinical significance and therapeutic response remain poorly understood.^3,10

Emerging research has identified noncanonical alterations that may contribute to myeloproliferation in the absence of classical driver mutations. ⁹ Among these mutations are SH2B3 mutations which have been reported in approximately 5–7% of triple-negative MPNs. ⁷ SH2B3 negatively regulates cytokine signaling and cell proliferation by attenuating JAK-STAT pathway activation. ¹¹ Loss-of-function mutations impair this mechanism, leading to increased signaling and uncontrolled myeloid production. ¹² In this case, a pathogenic SH2B3 mutation was detected at a high variant allele frequency of approximately 49%, suggesting its role as a driver in myeloid expansion.

This patient demonstrated clinical features consistent with a chronic myeloproliferative process. These characteristics included chronic leukocytosis, erythrocytosis, and thrombocytosis in addition to a hypercellular bone marrow with trilineage hematopoiesis and mild megakaryocytic atypia. Moreover, his bone marrow evaluation did show absence of excess blasts and lack of aberrant lymphoid populations on flow cytometry.

The treatment landscape for MPNs has included interferon alpha therapy for over 30 years. ⁸ Traditional interferon alpha has demonstrated significant disease-modifying effects, but its use is now limited due to reported toxicity. ¹³ Ropeginterferon alfa-2b, a novel and monopegylated interferon alfa-2b with an extended administration interval, has demonstrated a robust and sustained efficacy in PV patients and was approved by FDA in November 2021. ¹⁴ There are also ongoing clinical trials looking at the role of ropeginterferon alfa-2b in patients with myelofibrosis and essential thrombocytopenia.^15,16 However, its therapeutic role in triple-negative and SH2B3-mutated MPNs has not been well established.

This case underscores the utility of expanded molecular testing in triple-negative MPNs, as they may carry nonclassical clonal mutations. The detection of a SH2B3 mutation supported the initiation of ropeginterferon alfa-2b, given its ability to suppress clonal expansion. This treatment resulted in a complete hematologic response with excellent tolerability. To our knowledge, this is the first documented use of ropeginterferon alfa-2b in a patient with a SH2B3-mutated MPN. The successful response observed in this patient suggests that ropeginterferon alfa-2b may be an effective therapy in the management of MPNs driven by nonclassical mutations such as SH2B3.

Conclusion

This case reveals the significance of expanded molecular testing and suggests a potential role for ropeginterferon alfa-2b in patients with SH2B3-mutated, triple-negative MPNs. Further studies are needed to better understand the disease course and optimize therapeutic strategies in this group of patients.