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:

• Myeloblast [Compare]
• Pronormoblast [Compare]
• Immature B-cell (hematogone) [Compare]
• Monoblast [Compare]
• Prolymphocyte
• Reactive lymphocyte [Compare]

› 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+

› Cartoon Image:


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› Misc:

• 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.)