Introduction: The PCM1-JAK2 rearrangement is generated through the t(8; 9)(p22; p24) translocation event. The myeloid/lymphoid neoplasms with eosinophilia (MLN-eo) with PCM1-JAK2 rearrangement is the common types of MLN-eo with tyrosine kinase fusion genes (MLN-Eo-tk). MLN-Eo with PCM1-JAK2 rearrangement is a rare disease with a poor prognosis and no unified treatment guidelines. The response of disease to ruxolitinib may be transient and it may only serve as a temporary treatment prior to transplantation. Case Presentation: We report 1 patient diagnosed with MLN-Eo with PCM1-JAK2 rearrangement who exhibited resistance to ruxolitinib, subsequently received pegylated interferon (Peg-IFN) and lenalidomide. The Peg-IFN was discontinued due to adverse effects; the patient has been receiving lenalidomide monotherapy for a duration exceeding 2 years, achieving complete hematologic remission and molecular response, significant amelioration of symptoms, as well as regression of hepatosplenomegaly. Conclusion: A case of MLN-Eo with PCM1-JAK2 rearrangement underwent continuous oral lenalidomide monotherapy for over 2 years. The patient achieved complete hematologic remission and molecular response during the long-term follow-up; however, a complete molecular remission was not attained. The underlying mechanism of lenalidomide in these diseases necessitates further comprehensive investigation through fundamental research and clinical trials.
