Discrepancies between bone marrow histopathology and clinical phenotype in BCR-ABL1-negative myeloproliferative neoplasms associated with splanchnic vein thrombosis

• Splanchnic vein thrombosis is associated to MPNs in about half of cases.
• Search for JAK2 V617F in SVT patients is not always enough for the diagnosis of MPN.
• Bone marrow histology should represent a key component in SVT.
• Bone marrow histology is not enough to distinguish among PV, PMF or ET.
• An approach considering morphological, clinical and molecular data is needed.

We examined a consecutive series of 29 patients with myeloproliferative neoplasms (MPNs) associated with splanchnic vein thrombosis (SVT) in order to evaluate their bone marrow morphology and identify possible associations between histological findings and clinical features. Eleven patients showed the morphological features of polycythemia vera (PV), 11 of primary myelofibrosis (PMF) and six of essential thrombocythemia (ET). Molecular analyses identified the JAK2 V617F mutation in 27 patients; one of the JAK2-negative patients carried the MPL W515 K mutation, the other was “triple-negative” (no JAK2, MPL or CALR mutation). On the basis of the WHO classification, three patients were classified as having PV, 11 as having PMF, and two as having ET; the remaining 13 cases fell into the MPN-unclassifiable category as there were discrepancies between their morphological and clinical features.In conclusion, our findings suggest that bone marrow histology should always be considered a key component of the diagnostic algorithm in patients with SVT, but that it is not enough to distinguish the different entities. This is particularly important because diagnoses of PV, PMF or ET have very different prognoses and obviously imply different therapies. It is therefore necessary to adopt a comprehensive approach that considers morphological, clinical and molecular data.