The data from FCM and genetic analyses confirmed CD99 expression is higher in T-ALL cases than in normal BM cells.[16, 17] In addition, the FCM findings are consistent with previous reports, using the same monoclonal antibody clone, identifying CD99 as a useful discriminator of T-ALL blasts from normal T lymphocytes.[15, 16] During T cell development CD99 is downregulated on normal T-cells with increasing expression of surface CD3.[25] CD99 was highly expressed in the current patient cohort, regardless of prognostic indicators or MRD risk status. Here, CD99 is linked to acute lymphoblastic leukemia.