Surgical Pathology Criteria

Precursor T Lymphoblastic Leukemia / Lymphoma

Differential Diagnosis

Type B1 Thymoma Precursor T Lymphoblastic Leukemia / Lymphoma
Scattered epithelial cells (may require anti-keratin stain) Only keratin positive cells should be overrun thymus
Scattered pale medullary foci Lacks medullary foci
Thick fibrous capsule and septa produce large lobules Lacks thick fibrous capsule and septa and lobular growth pattern
Typically older adult but may occur in children Typically adolescent or pediatric
No circulating blasts Circulating blasts
Variable expression of surface CD3, CD4, CD8 in a given case Uniform phenotype in a given case
  • Lymphocytes have same basic phenotype in both: predominantly immature T cells with mature T cells restricted to medullary foci
  • May be a significant problem on small biopsies and in cases analyzed by flow
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    Normal Thymus Precursor T Lymphoblastic Leukemia / Lymphoma
    No circulating blasts Circulating blasts
    Histopathology shows normal epithelial component No neoplastic epithelial component on histopathology (effaced epithelial component may be present)
    Histopathology shows lobularity with cortical / medullary differentiation Histopathology shows no normal architecture
    Flow cytometry of normal thymus will show a preponderance of precursor T cells with a phenotype that may be indistinguishable from leukemia / lymphoma

     

    Precursor B Lymphoblastic Leukemia / Lymphoma Precursor T Lymphoblastic Leukemia / Lymphoma
    10% of precursor lymphoblastic lymphomas 90% of precursor lymphoblastic lymphomas
    Frequently involves skin and bone Frequent mediastinal mass
    B lineage (usually CD19+, CD79a+ at a minimum) T lineage (usually CD3+, CD7+ at a minimum)
    Both are TdT+ and may be CD34+

     

    Burkitt Lymphoma Precursor T Lymphoblastic Leukemia / Lymphoma
    Presents as soft tissue mass, rarely mediastinal Frequently presents as mediastinal mass
    B cell phenotype (usually CD19+, CD20+, CD79a+) T cell phenotype (usually CD3+, CD7+ at a minimum)
    Mature phenotype (TdT and CD34 negative) Immature phenotype (usually TdT+, sometimes CD34+)
    Translocation involving myc gene No myc translocation

     

    CD4+ CD56+ Hematodermic Neoplasm (Blastic NK Cell Lymphoma) Precursor T Lymphoblastic Leukemia / Lymphoma
    Skin lesions usually predominate Frequently presents as mediastinal mass
    Usually negative for T cell markers (rare cases may be positive for TdT) Immature T cell phenotype (usually CD3+, CD7+, TdT+ at a minimum)

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