CD33 is an excellent myeloid cell marker and is commonly used for the diagnosis of Acute myeloid leukemia (AML). About 85-90% pediatric & adult AML are CD33 positive. The expression of CD33 is 100% in AML M0; 75-85% in AML M1 to M5; variable in AML M7. However, about 10-20% cases of B-cell / T-cell lymphoblastic leukemias & lymphomas may aberrantly express CD33.