Precursor T Lymphoblastic Leukemia / Lymphoma
Supplemental Studies
Immunohistology and Flow Cytometry
- Non-lineage specific markers
- TdT > 95%
- CD10 subset of cases
- CD34 subset of cases
- T lineage markers
- Usually positive:
- CD3 (highly lineage-specific)
- cytoplasmic CD3 >95% of cases
- surface CD3 infrequent
- CD7 >95% of cases
- Subset of cases positive:
- CD1a
- CD2
- CD5
- CD4
- CD8
- CD4, CD8 double positive ~50%
- Aberrant lineage markers expressed in a minority of cases
- B-lineage
- CD79a (10%)
- Myeloid
- CD13, CD33 and others (~15%)
- These markers alone are not sufficient for a leukemia to be considered biphenotypic (e.g. combined B and T lineage or combined T and myeloid lineage)
- See the scoring criteria below for further information
- Scoring system for lineage assignment of leukemias by the European Group for the Immunologic Classification (EGIL)
Score
B-lymphoid
T-lymphoid
Myeloid
2
Cytoplasmic CD79a*
CD3 (membrane/cytoplasmic)
MPO
Cytoplasmic IgM
Anti-TCR
Cytoplasmic CD22
1
CD19
CD2
CD117
CD20
CD5
CD13
CD10
CD8
CD33
CD10
CD65
0.5
TdT
TdT
CD14
CD24
CD7
CD15
CD1a
CD64
- A score of 2.5 is considered sufficient to assign a lineage
- CD79a may also be expressed in a subset of T lymphoblastic leukemia/lymphoma
Genetic study
- Cytogenetic/molecular studies show abnormalities in > 50% of cases
- May be useful in monitoring for residual disease, but unlike in B-lymphoblastic lymphoma/leukemia, do not add prognostic information
- May show clonal T cell receptor rearrangement
