Model of leukemic transformation in MPD. Some patients develop JAK2V617F⁺ AML after JAK2V617F⁺ MPD, consistent with a JAK2V617F⁺ progenitor that undergoes leukemic transformation. However, some patients with JAK2V617F⁺ MPD transform to a JAK2V617F⁻ AML, consistent with a “pre-JAK2” clone, which is susceptible to leukemic transformation. Illustration by Debra Tyler.