Flow Cytometry:T-Lymphoid lineage assignment in MPAL
From haematologyetc.co.uk
| Mixed Phenotype Acute Leukaemia (MPAL): basics |
MPAL requires a diagnosis of acute leukaemia (>20% blast cells) but in which differentiation does not occur along a single lineage. This diagnosis is uncommon (2-3% of acute leukaemia).
Flow cytometry provides initial evidence of MPAL. However conclusions may subsequently be modified (e.g. by results of immunohistochemistry, cytogenetics, or genetics). It is important that the provisional nature of flow cytometry assignment of MPAL is acknowledged.
Types and frequency of MPAL types
(1) MPAL with features of Myeloid and B-lineage (MPAL M/B) (>50% cases)
(2) MPAL with features of Myeloid and T-lineage (MPAL M/T) (>33% cases)
(3) MPAL with combinations: MPAL B/T (rare) or B/T/M (very rare)
Following further analysis cases may be assigned additionally as:
- MPAL with t(9;22) (q34.1;q11.2); BCR-ABL1;
- MPAL with t(v;11q23.3); with KMT2A re-arrangement
| Mixed phenotype: biphenotypic pattern, bilineal pattern and blast cell number |
The blast population may express markers of the two separate lineages both on the same cell (bi-phenotypic pattern) in which case blast number must exceed 20%, alternatively the blast cells may have two lineages that co-exist (bi-lineal pattern) in which case the combined blast cell number must exceed 20%.
| Mixed phenotype: diagnosis |
To diagnose MPAL, the leukaemia should meet at least two of the three criteria below: .
| Criteria to assign myeloid lineage | |
|---|---|
| The case has lineage-defining features of myeloid maturation. This allows myeloid lineage to be defined in MPAL Click here to review criteria for myeloid lineage assignment based on lineage-defining features Note: myeloid-associated lineage markers cannot be contribute to myeloid lineage assignment in MPAL. | |
| Criteria to assign B-lymphoid lineage | |
| The case has lineage-defining features of B-lymphoid maturation. This allows B-lymphoid lineage to be defined in MPAL Click here to review criteria for B-lymphoid lineage assignment Note Where T-lineage is also considered the diagnostic value of CD79A is reduced so should not be considered in the lineage assignment. | |
| Criteria to assign T-lymphoid lineage | |
| Click here to review criteria for T-lymphoid lineage assignment |
Consider also: