Visualization of clonal expansion of TP53-mutated cells. Immunohistochemical staining for p53 protein expression on BM biopsies at tMN diagnosis and preleukemic time points for patients UPN17 (A), UPN01 (B), and UPN03 (C). Time points of biopsy and magnification are indicated in the figure panels. (D) Percentage of cells showing high p53 protein expression (p53⁺⁺ cells) were scored at different time points (pre- and post-ASCT) for the 3 patients depicted in panels A-C; last time point is moment of tMN diagnosis.