Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Abnormal

T-Lymphoblasts (Increased)*

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Microscopic Features:
  • 3-4x larger than a mature RBC
  • High nuclear to cytoplasmic ratio
  • Round Nucleus with immature chromatin (not clumped)
  • Prominent nucleoli
  • Cytoplasm is scant, light blue and lacks granules
Normal % blood-PB, marrow-BM, lymphoid tissue-LN:
  • PB: None
  • BM: Rare (~1%)
  • LN: None
May Resemble: Differential Diagnoses:

If in blood or increased numbers in bone marrow:
T-Lymphoblastic leukemia (T-ALL)
Rarely some non-neoplastic conditions

Classic Immunophenotype:
  • CD3+ (cytoplasmic)
  • CD7+
  • CD34+
  • TdT+
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  • Blasts cells cannot be reliably distinguished from each other based on morphology alone. The exception are blasts with Auer Rod(s) which are unique to abnormal Myeloblast {16}s and abnormal promyelocytes as noted in some AMLs and APL Note: Abnormal lymphoblasts can show immunophenotypic abberancies (e.g. loss of T-cell antigens such as CD7, CD5 and CD2 or the gain of myeloid markers such as CD13, etc.)

Content Editors/Website Administrators:
Hooman H. Rashidi, MD; John C. Nguyen, MD