CD9 and acute promyelocytic leukemia: Touzet et al9 observed that CD9 expression was increased in 40% of AML cases and was associated with a favorable prognosis.9 Other studies explored CD9 as a useful marker in identifying acute promyelocytic leukemia (APL), including as a marker of residual disease,10-14 and AML with the NPM1 mutation in certain cohorts.15 In contrast, AML with RUNX1::RUNX1T1 was reported to have lower CD9 expression based on publicly available gene expression data.16-18