Synchronous Coexistence of JAK2 V617F-Positive Essential Thrombocythemia and IgG Kappa Multiple Myeloma in an...

The synchronous coexistence of JAK2 V617F-positive essential thrombocythemia (ET) and IgG kappa multiple myeloma (MM) is exceptionally rare, with fewer than 10 synchronous cases reported in the literature. The present case is unique in that MM was discovered incidentally during systematic bone marrow evaluation for isolated thrombocytosis in an octogenarian with significant comorbidities, requiring the concurrent management of two independent clonal hematological neoplasms. An 81-year-old woman with prior hypertension and cerebrovascular disease was referred for persistent thrombocytosis exceeding 1,000,000 platelets/μL. Systematic bone marrow evaluation led to the incidental identification of a monoclonal kappa plasma cell population, prompting full myeloma workup. JAK2 V617F-positive high-risk ET and IgG kappa MM (ISS Stage II) were diagnosed synchronously. Acquired von Willebrand syndrome was excluded prior to any anticoagulation decision. Treatment included hydroxyurea-subsequently switched to anagrelide due to a national drug supply shortage-for ET cytoreduction, and a bortezomib-dexamethasone-lenalidomide (VRD) regimen for MM. An IMWG partial response was achieved after three cycles, with adequate platelet control at 8 months of follow-up. This case underscores the importance of systematic bone marrow evaluation in myeloproliferative neoplasms, as it may unmask concurrent plasma cell dyscrasias. Several pathophysiological mechanisms-including IL-6-mediated microenvironmental activation, BAFF-driven B-cell proliferation, and a shared inflammatory niche-have been proposed in the literature to explain this co-occurrence; however, these were not directly evaluated in this patient. The regimen chosen was guided by clinical complexity and resource constraints rather than current preferred first-line guidelines, which favor daratumumab-based combinations for transplant-ineligible patients. Early identification of coexisting clonal neoplasms substantially impacts prognosis and therapeutic decision-making.