CD9 and acute promyelocytic leukemia: Additionally, we compared the levels of CD9 expression in leukemic blasts, using the most updated classification schemes, comparing subtypes not included in previous studies (APL often omitted when comparing large AML cohorts).9,15 Given that this study is retrospective, utilizing the clinically available MFC assay performed in our clinical laboratory for patients with newly diagnosed acute leukemia, we were limited to reviewing the panels already performed for our patients with AML.