Interestingly, we observed a remarkable increase in OPN plasma levels in JAK2V617F knock-in animals at the age they develop myelofibrosis in line with results from MPN patients where OPN plasma levels were remarkably higher in PMF versus Essential Thrombocythemia and Polycythemia Vera patients, as well as in overt versus pre-fibrotic PMF patients [16]. Here, SPP1 is linked to acquired polycythemia vera.