The two cases just shown illustrate the morphologic variation that occurs in ALL, and this variation has prompted attempts to subclassify ALL on the basis of blast morphology. The most widely recognized classification was proposed by a group of French, American, and British hematologists, and it is called the FAB classification. Table 2 lists some of the features that distinguish the three FAB subclasses of ALL. The type commonly seen in children is L1. The case in slides 7 and 8 would be in this category. Blasts are relatively small but vary somewhat in size, and the nuclear chromatin and size are fairly similar from cell to cell in any given case. More commonly seen in adults is L2 ALL, and the case in slide 9 would be put into this category. The cytologic appearance of blasts in these L2 cases is very heterogeneous: Cell size and shape, nuclear shape and chromatin pattern, appearance of nucleoli, and amount of cytoplasm vary substantially even in a single patient. Type L3, or Burkitt's ALL, is the least common of the three types. The next slide shows the bone marrow from a patient with L3 ALL.
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Course Section: 07. Lymphocytic Leukemia: Acute and Chronic
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