CD34 and fibrosis: In patients with PMF the CD34+ cell constitutive p-STAT5 MFI values were significantly inversely correlated with hemoglobin levels (R = -0.28, p = 0.037), one of the most relevant hematological and clinical variable, whose variations portrait disease progression; no correlation was found with IPSS, DIPSS, WBC, monocyte, or platelet count, frequency of circulating blood blasts, serum LDH, spleen size and degree of BM fibrosis (S1 Table).