A 46-year-old woman presents with a long-lasting history of thrombocytosis (mean platelets: 500 × 109/L) and a putative clinical diagnosis of ET treated with low-dose aspirin. A BM biopsy () is performed 20 years after clinical onset and shows hypercellular, trilinear hematopoiesis with normal myeloid-to-erythroid ratio, mildly left shifted granulopoiesis, and increased, mature-looking megakaryocytes. Blasts account for 3–4% of the hematopoietic cells and reticulin fibrosis is not increased. Driver mutations of JAK2, CALR and MPL are not detected, but targeted NGS documents the L56S RUNX1 variant. The overall morphological and molecular findings exclude ET and suggest an alternative diagnosis of RUNX1-mutated myeloid neoplasm with thrombocytosis.\nGermline RUNX1 mutations are reported in inherited forms of platelet disorders with a predisposition to myeloid malignancies []. Acquired RUNX1 derangements are instead relatively common in MDS, MDS/MPN, AML, and in contexts akin to CHIP []. In the present case, the unremarkable family history, the clinical presentation, and the histological findings exclude such diagnoses and favors MPN-U. Of note, rare cases of MPN feature RUNX1 mutations and typically undergo myelofibrotic and/or blastic progression [,]. This and 3 similar cases published by Cattaneo and colleagues [] disclose the unique features of an MPN with “high risk” genetics and an indolent, ET-like clinical course.
A 32-year old pregnant woman refers to the Emergency Unit for abdominal pain. Sonography reveals SVT of the splenic-portal axis and blood tests disclose anemia (Hb = 10.5 g/dL; Hct = 32%), leukocytosis (WBC = 18.2 × 109/L), and thrombocytosis (Plt = 596 × 109/L) with low Epo levels (3.3 mU/mL [4.3–29]), and JAK2 mutation. A BM biopsy (a–c) discloses PV changes with hypercellularity, expansion of the three hematopoietic lineages, clustering of polymorphic megakaryocytes, and no fibrosis. Despite this, the lack of the first major criterion hampers a formal diagnosis of PV.\nThe present case depicts the prototypic features of “masked PV”, presenting with SVT. A further bias is the concurrent pregnancy, which itself favors deep vein thrombosis. Such a clinical event may occur in any subtype of MPN, either at diagnosis or during the course of the disease. A higher thrombotic risk is related to a hyperinflammatory state and neutrophilia, which are more commonly experienced in PV []. Besides the diagnostic issues, it should be stressed that thrombotic events pose the highest threat for patients with early phase MPN. Despite the risk factors for vascular events are only partially defined, major determinants include JAK2 status, age, neutrophil count, and a positive history of thrombosis [,,].