SPARC stromal expression and features of BM failure are correlated in myelofibrotic myeloid malignancies. (A) Immunohistochemical analysis of SPARC expression (aminoethyl-carbazole [AEC], red signal) on BM sections from control (Reactive BM) and myeloid neoplasm (MDS-F; PMF-3) cases. In normal BM that is free of stromal alterations, SPARC expression is confined to MKs (left panel, black arrows, inset). However, in marrow with myeloproliferation-associated stromal alterations, SPARC reactivity extends to stromal cells with spindle to stellate morphology (central and right panels, green arrows, insets). Three representative cases of the 114 cases evaluated are shown. Original magnifications ×200, insets ×630. Scale bars represent 100 μm. (B) The number of SPARC⁺ stromal cells, assessed in 56 PMF cases, is significantly correlated with relevant biologic, clinical, and prognostic features: BM fibrosis; prognostic risk group according to Cervantes et al.³¹  MVD; CD146⁺ mesenchymal stromal cells. *P < .05. Box plot and scattergrams have been plotted to allow distinction between early (prefibrotic/grade 1 fibrosis) and advanced PMF cases (grade 2 or 3 fibrosis).