A 10 year old child presents with pallor & history of blood transfusion 2 months back. On investigation, Hb -4.5gm, total count 60000, platelet count- 2lakhs and CD 10(+) ve, CD 19 (+)ve, CD 117 (+) ve, MPO (+) ve & CD 33(-)ve. What is the most likely diagnosis?

Ans. is 'd' i.e., Mixed phenotypic acute leukemia o Immunological markers in this question are :- o CD 10 (+) ye, CD 19(+) ye --> B cell lineage Myeloperoxidase (MPO) ( +)ve, CD117 (+)ve Myeloid lineage o Immunological markers of two lineage are present. Therefore,it is a case of biphenotypic leukemia (mixed phenotypic leukemia). o Biphenotypic leukemia is a subtype of "leukemia of ambiguous lineage" (a new class of AML which has been added in 18th/e of Harrison. But in Harrison, detailed description of this class has not been given.. Acute leukemia with Ambiguous lineage 3 Human acute leukemias are broadly classified as myeloid or lymphoid according to the expression of surface and/or cytoplasmic antigens. o Uncommonly, the lineage of origin is not clear ; either two separate blast populations are encountered, one myeloid and other lymphoid, or a single blast population demonstrating evidence of both myeloid and lymphoid differentiation concurrently. o Acute leukemia with ambiguous lineage has following subtypes :-. A) Acute undifferentiated leukemia In this leukemia, the blast cells express none of the antigen that are useful in lineage attribution but rather express only markers that are linked to high stages of immaturity such as CD 34, CD 38 and HLA-DR and at times CD 7. B) Mixed phenotypic acute leukemia In this type of leukemia, immunological marker of more than one lineage are present. This is classifed intoi) Bilinear acute leukemia o In this, two separate blast populations are encountered. o For example blast cells of lymphoid and myeloid lineage are present simultaneously. n) Biphenotypic acute leukemia o Bipheotypic acute leukemia is also called " hybrid acute leukemia" or " acute mixed lineage leukemia" or "simultaneous leukemia'. o In this leukemia, a single blast population demonstrates marker of more than one lineage (in contrast to bilinear leukemia where blasts of two different lineage are present). o Coexpression of myeloid with B lymphoid lineage is most common type (65%). Co-presence of myeloid with T-lymphoid lineage is second most common type. Co-expression of T and B cells phenotype or trilineage phenotype (T, B and myeloid cells) is rare. o According to the 2008 WHO classification, the requirements for lineage attribution are as follows :? a) Myeloid lineage :- Presence of myeloperoxidase or at least 2 markers of monocytic differentiation CD11c, CD 14, CD64, lysozyme, non-specific esterase b) T lineage :- Cytoplasmic or surface CD3 c) B lineage :- Strong CD19 expression with at least one of the following weakly expressed CD 10, CD 79a, cytoplasmic CD22; or weak CD 19 expression with at least 2 of the following strongly expressed CD 10, CD 79a, cytoplasmic CD22. Clinical presentation o Similar to other acute leukemias, acute leukemia with ambiguous lineage presents with symptoms related to depression of marrow function, i.e., cytopenia i.e. anemia, leukopenia, thrombocytopenia or pancytopenia. Coming back to question o Expression of B lineage (CD19 with CD 10) and myeloid lineage ( myeloperoxidase) confirms the diagnosis of biphenotypic leukemia.