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Slide 22
This area of a bone marrow contains all blasts except for the cell, a promyelocyte, indicated by the arrow. The marrow is myeloblastic and fits the FAB classification M1. However, it is very difficult to differentiate these blasts from lymphoblasts or monoblasts. Even an experienced morphologist is correct only about 75%-85% of the time in such cases.

The cells in this field are basophilic, the nucleoli are not prominent, and the N:C ratio is extremely high. The cells have no granules. One feature that is common to ALL is variability in cell size; there is less variability in AML. Another difference is the nuclear chromatin, which is finer and more homogeneous in myeloblasts than in lymphoblasts. The marrow shown here requires special stains for a definite diagnosis.

Course Section: 08. Myelocytic Leukemia: Chronic and Acute
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