blast
An immature blood cell that has undergone malignant transformation in leukemia.
Full Definition
Blasts are immature hematopoietic cells that represent the malignant cell population in acute leukemias. In normal hematopoiesis, blasts comprise less than 5% of bone marrow cells, but in acute leukemia, they typically exceed 20% (or 25% by some classification systems). Morphologically, blasts are characterized by large nuclei with fine chromatin, prominent nucleoli, and scant cytoplasm. The percentage of blasts in bone marrow and peripheral blood is used for diagnosis, classification, and monitoring treatment response. Different blast subtypes (lymphoblasts vs. myeloblasts) help distinguish between acute lymphoblastic leukemia and acute myeloid leukemia.
Usage
Usage note: Always specify percentage when reporting blast counts and the tissue source (bone marrow vs. peripheral blood).
In Context
- "Bone marrow examination revealed 85% blasts consistent with acute leukemia." — Pathology report
- "The patient achieved morphologic remission with less than 5% blasts in bone marrow." — Response assessment