T-cell Large Granular Lymphocytic Leukemia (T-LGL)

T-LGL leukemia represents only 2-3% of mature lymphocytic leukemias.  Classically patients present with neutropenia and splenomegaly.  Most patients don’t die from the leukemia itself, but accompanying diseases/cytopenias.  The peripheral blood LGL count is usually between 2-20x10e9/L.  THere is a significant gray-zone of uncertainty between what constitutes a benign population of LGLs and a neoplastic process (possibly an immune response that turns neoplastic??).
Features
  • Pathophysiology is NOT well understood
  • STAT3 mutated in approximately 1/3rd of cases (rarely STAT5B)
  • LGL count >2,000/μL (cases with <2,000/μL can be diagnosed if all other criteria are consistent with T-LGL leukemia
    • “All other criteria” are not well-described
  • Cases that resemble T-LGL but lack surface CD3 (sCD3) are classified in the NK-cell disorders.
Characteristic Immunophenotype
Stain
Comment
Positive
Usually Negative.  A subset of cases may express CD4.  CD4 + cases have been associated with an underlying malignancy  (~30% of cases).
+/- (May have diminished or lost expression)
+/- (May have diminished or lost expression)
Usually Positive
Granzyme_B
Usually Positive
TIA-1
Positive
CD57
Positive (>80% of cases)
Usually negative
References
Swerdlow SH, Campo E, Harris, NL, Jaffe ES, Pileri SA, Stein H, Thiele J (Eds):  WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (Revised 4th edition). IARC: Lyon 2017
 
Hematopathology. [edited by] Jaffe, ES. 1st. ed. Elsevier, Inc. © 2011.