V617F^- leukemic transformation developed in 3 of 4 patients with a preceding V617F⁺ MPD. (A) Paired sequence traces on 2 patients with PV from the PV phase (top panel) and leukemic phase (middle panel) of disease showing reversion of mutated nucleotide (arrowheads) to WT. Bottom panels are smears from samples used for sequencing (bone marrow aspirate for PV1 and peripheral-blood mononuclear cells for PV2). (B) Sequence traces from bone marrow samples taken after leukemic transformation in 2 patients with ET (top panel). Samples from before AML transformation showed both patients to be V617F⁺ by allele-specific PCR (data not shown). Both samples had high percentage of blast cells in their bone marrow aspirates (bottom panels). Romanowsky-stained slides were imaged on an Olympus BX51 microscope (Olympus, Center Valley, PA) equipped with a 40×/0.85 oil-immersion objective lens. A Pixera Penguin 600CL camera (Pixera, Los Gatos, CA) was used to capture images, and Viewfinder 3.0.1 (Pixera) was used to acquire them.