Clonal evolution during progression from MDS to secondary AML. Using previously published paired MDS and secondary AML samples from the same patients (N = 60),^{17,18,23,65,66,88}  the order of mutation acquisition was inferred by assessing the presence or absence of specific mutations at each sampling. (A) A model for sequential accumulation of mutations during progression from MDS to secondary AML. Black cells are normal at MDS and secondary AML. Mutations in blue are acquired early, define the founding clone, and expand to become the most abundant clone in the marrow at MDS diagnosis. These cells then acquire red mutations, form a subclone, and expand at the time of progression to secondary AML. (B) Percentage of patients with a mutation detectable at MDS only (yellow), secondary AML only (red), or at MDS and persisting during disease progression (blue). Mutations in specific functional categories are enriched in 1 of these patterns, with most TP53, epigenetic modifiers, and spliceosome gene mutations present at MDS (eg, 100% of DNMT3A mutations are blue), whereas mutations in transcription factors (eg, RUNX1, CEBPA) and activating signaling genes (RAS family, PTPN11, FLT3) typically expand or are acquired and emerge at progression (eg, 100% of FLT3 mutations are red). This suggests a typical order of mutation acquisition, with blue mutations being acquired early and present in the majority of marrow cells at MDS diagnosis, followed by the red mutations, which expand or are acquired and expand at progression. Only 1 mutation (shown in yellow) that was detected at MDS was not detected at secondary AML (SRSF2 mutation coding for the P95R substitution).⁸⁸  Adapted from Lindsley et al.⁶⁵