B Lymphoblastic Leukemia:
B-ALL is diagnosed if CD19, CyCD22, CyCD79a or PAX5 is expressed and does not fulfil the criteria to diagnose acute leukemia of ambiguous lineage (See Fig 1).
Typical B-ALL cases with only a single blast population and weak MPO expression by flow cytometry as the only evidence of myeloid differentiation should not be diagnosed as mixed phenotype acute leukemia.
Fig 1. B-ALL. Blasts (red) are positive for CD19 and CyCD79a. T-cells (dark blue) can be used as negative control. Normal B-cells (green) can be used as positive control. Bright CD19 expression is defined as brightest CD19+ blasts should reach the intensity of the normal B-cells.
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