Peripheral blood and bone marrow findings before and after treatment with PKC 412. (A-F) Before treatment. (G-I) After treatment. (A) Circulating mast cell (arrow, left) and dysplastic nucleated red blood cell (arrowhead, right) in peripheral blood. Wright-Giemsa, 1000 ×. (B) Hypercellular bone marrow with aggregates of pale-staining mast cells surrounding a dilated sinus (^*). Hematoxylin and eosin, 40 ×. (C) Whorled nodule of mast cells with characteristic clear cytoplasm including spindled forms. Hematoxylin and eosin, 400 ×. (D) Increased mast cells show a nodular and interstitial pattern in the bone marrow occupying approximately 70% marrow cellularity. Mast cell tryptase, 40 ×. (E) The majority of mast cells are highlighted by CD25 antibody. CD25, 40 ×. (F) Few numbers of CD34-positive blasts (∼5%) detected on bone marrow biopsy. CD34, 400 ×. (G) The posttreatment bone marrow shows a similar mast cell burden as seen prior to treatment. Mast cell tryptase, 40 ×. (H) A slight decrease in CD25-positive mast cells (∼40% of marrow cellularity) is noted after therapy. CD25, 40 ×. (I) Increased numbers of CD34-positive blasts (10%-20%) in bone marrow biopsy indicating progression of this patient's AHNDMD, MDS/MPD. CD34, 400 ×.