CD9 and acute promyelocytic leukemia: Our study confirms others’ findings that increased CD9 expression can help differentiate APL from most other AMLs,10-12,14 and leukemic blasts often have higher CD9 expression than normal myeloid blasts.9 Although there are certainly higher-sensitivity molecular methods to assess for APL posttherapy, we also determined that normal promyelocytes express much lower CD9 compared to leukemic APL blast equivalents (which was statistically significant), supporting Wen et al14 in the use of CD9 posttherapy.