Chronic eosinophilic leukemia with erythroblastic proliferation and the rare translocation t(8;9)(p22;p24) withPCM1–JAK2fusion gene: a distinct clinical, pathological and genetic entity with potential treatment target?

TLE3 Is a Novel Fusion Partner of JAK2 in Myeloid/Lymphoid Neoplasm With Eosinophilia Responding to JAK2 Inhibition

Chromosomal rearrangements involving Janus kinase 2 (JAK2) are rare but recurrent findings in lymphoid or myeloid neoplasia. Detection of JAK2 fusion genes is important as patients with aberrantly activated JAK2 may benefit from treatment with tyrosine kinase inhibitors such as ruxolitinib. Here, we report a novel fusion gene between the transcriptional co-repressor-encoding gene transducin-like enhancer of split 3 (TLE3) and JAK2 in a patient initially diagnosed with chronic eosinophilic leukemia with additional mutations in PTPN11 and NRAS. The patient was successfully treated with the JAK2 inhibitor ruxolitinib for 8 months before additional somatic mutations were acquired and the disease progressed into an acute lymphoblastic T-cell leukemia/lymphoma. The present case shows similarities to previously reported cases with PCM1::JAK2 and BCR::JAK2 with regard to disease phenotype and response to ruxolitinib, and importantly, provides an example that also patients harboring other JAK2 fusion genes may benefit from treatment with JAK2 inhibitors.

Sustained Response to Ruxolitinib of Eosinophilia-Associated Myeloproliferative Neoplasm with Translocation t(8;9)(p21;p24)

The translocation t(8;9) produces the fusion gene PCM1-JAK2, resulting in the continuous activation of the JAK2 tyrosine kinase. Myelodysplastic/myeloproliferative neoplasms are the most common disease with t(8;9)/PCM1-JAK2. Individuals with this abnormality have similar features, and JAK2 kinase inhibitor (ruxolitinib) is an effective treatment of the condition. The long-term remission results of ruxolitinib are varied. It is important to determine the response to ruxolitinib. Here, we describe a patient who has been diagnosed with eosinophilia-associated myeloproliferative neoplasm with t(8;9)(p21;p24). This patient has achieved sustained response for >1 year since the administration of ruxolitinib.

OUP accepted manuscript

Background

This review summarizes the case studies of PCM1-JAK2 fusion tyrosine kinase gene-related neoplasia. Recommended treatment includes JAK2 inhibitors and hematologic stem cell transplantation (HSCT), although the small number of patients has limited study of their efficacy. Herein, we present all available cases in the current searchable literature with their demographics, diagnoses, treatments, and outcomes.

Methods

PubMed, ScienceDirect, Publons, the Cochrane Library, and Google were searched with the following terms: PCM1-JAK2, ruxolitinib and myeloid/lymphoid.

Results

Sixty-six patients (mean age = 50, 77% male) had an initial diagnosis of myeloproliferative neoplasm (MPN) in 40, acute leukemia in 21 and T-cell cutaneous lymphoma in 5. Thirty-five patients (53%) had completed 5-year follow-up. The 5-year survival for the MPN, acute myelogenous leukemia (AML), acute lymphocytic leukemia, and lymphoma groups are 62.7, 14.9%, 40.0%, and 100%, respectively. Too few patients have been treated with ruxolitinib to draw conclusions regarding its effect on survival while the 5-year survival for MPN patients with or without HSCT was 80.2% (40.3%-94.8%) versus 51.5% (22.3%-74.6%), respectively. The T-cell cutaneous lymphoma patients have all survived at least 7 years.

Conclusion

This rare condition may be increasingly detected with wider use of genomics. Ruxolitinib can yield hematologic and molecular remissions. However, HSCT is, at this time, the only potentially curative treatment. Useful prognostic markers are needed to determine appropriate timing for HSCT in patients with MPN. Patients presenting with acute leukemia have a poor prognosis.

Diagnosis and Treatment of Myeloproliferative Neoplasms With PCM1-JAK2 Rearrangement: Case Report and Literature Review

Myeloproliferative neoplasm (MPN) with PCM1-JAK2 rearrangement is a rare disease with poor prognosis and lacks uniform treatment guidelines. Several studies confirmed the efficacy of ruxolitinib in hematological malignancies with PCM1-JAK2 fusion, but the efficacy is variable. Here, we report two patients diagnosed with MPN with PCM1-JAK2 fusion who were treated with ruxolitinib-based regimen, including the first case of ruxolitinib combined with pegylated interferon (Peg-IFN), and we conduct a literature review. We found that ruxolitinib combined with Peg-IFN is an effective treatment option in the case of poor efficacy of ruxolitinib monotherapy.

Response to tyrosine kinase inhibitors in myeloid neoplasms associated with PCM1-JAK2, BCR-JAK2 and ETV6-ABL1 fusion genes

We report on 18 patients with myeloid neoplasms and associated tyrosine kinase (TK) fusion genes on treatment with the TK inhibitors (TKI) ruxolitinib (PCM1-JAK2, n = 8; BCR-JAK2, n = 1) and imatinib, nilotinib or dasatinib (ETV6-ABL1, n = 9). On ruxolitinib (median 24 months, range 2-36 months), a complete hematologic response (CHR) and complete cytogenetic response (CCR) was achieved by five of nine and two of nine patients, respectively. However, ruxolitinib was stopped in eight of nine patients because of primary resistance (n = 3), progression (n = 3) or planned allogeneic stem cell transplantation (allo SCT, n = 2). At a median of 36 months (range 4-78 months) from diagnosis, five of nine patients are alive: four of six patients after allo SCT and one patient who remains on ruxolitinib. In ETV6-ABL1 positive patients, a durable CHR was achieved by four of nine patients (imatinib with one of five, nilotinib with two of three, dasatinib with one of one). Because of inadequate efficacy (lack of hematological and/or cytogenetic/molecular response), six of nine patients (imatinib, n = 5; nilotinib, n = 1) were switched to nilotinib or dasatinib. At a median of 23 months (range 3-60 months) from diagnosis, five of nine patients are in CCR or complete molecular response (nilotinib, n = 2; dasatinib, n = 2; allo SCT, n = 1) while two of nine patients have died. We conclude that (a) responses on ruxolitinib may only be transient in the majority of JAK2 fusion gene positive patients with allo SCT being an important early treatment option, and (b) nilotinib or dasatinib may be more effective than imatinib to induce durable complete remissions in ETV6-ABL1 positive patients.

t(8;9)(p22;p24)/PCM1-JAK2 activates SOCS2 and SOCS3 via STAT5

Fusions of the tyrosine kinase domain of JAK2 with multiple partners occur in leukemia/lymphoma where they reportedly promote JAK2-oligomerization and autonomous signalling, Affected entities are promising candidates for therapy with JAK2 signalling inhibitors. While JAK2-translocations occur in myeloid, B-cell and T-cell lymphoid neoplasms, our findings suggest their incidence among the last group is low. Here we describe the genomic, transcriptional and signalling characteristics of PCM1-JAK2 formed by t(8;9)(p22;p24) in a trio of cell lines established at indolent (MAC-1) and aggressive (MAC-2A/2B) phases of a cutaneous T-cell lymphoma (CTCL). To investigate signalling, PCM1-JAK2 was subjected to lentiviral knockdown which inhibited 7 top upregulated genes in t(8;9) cells, notably SOCS2/3. SOCS3, but not SOCS2, was also upregulated in a chronic eosinophilic leukemia bearing PCM1-JAK2, highlighting its role as a central signalling target of JAK2 translocation neoplasia. Conversely, expression of GATA3, a key T-cell developmental gene silenced in aggressive lymphoma cells, was partially restored by PCM1-JAK2 knockdown. Treatment with a selective JAK2 inhibitor (TG101348) to which MAC-1/2A/2B cells were conspicuously sensitive confirmed knockdown results and highlighted JAK2 as the active moiety. PCM1-JAK2 signalling required pSTAT5, supporting a general paradigm of STAT5 activation by JAK2 alterations in lymphoid malignancies. MAC-1/2A/2B - the first JAK2–translocation leukemia/lymphoma cell lines described - display conspicuous JAK/STAT signalling accompanied by T-cell developmental and autoimmune disease gene expression signatures, confirming their fitness as CTCL disease models. Our data support further investigation of SOCS2/3 as signalling effectors, prognostic indicators and potential therapeutic targets in cancers with JAK2 rearrangements.