Morphologic Classification

The French-American-British (FAB) classification system separated AML and ALL based on the visual microscopic appearance of blast forms in peripheral blood and bone marrow, as well as on the activity of selected special enzymatic stains, such as peroxidase, specific and nonspecific esterase, and periodic acid-Schiff for glycogen.49 Morphologic classification with the FAB system separates three forms of ALL. ALL includes50:

Figure 10.2 L1—uniform small peripheral lymphoid blasts with minimal to moderate cytoplasm, effaced chro-matin, and occasional to more numerous nucleoli

Figure 10.3 L2—variable-sized peripheral blood lym-phoblasts with variable chromatin pattern and more frequent nucleoli

LI—Small lymphocytic variant with uniform small cells having a more "mature" appearance (Figure 10.2). L2—Variable cell size with large and small cells in the same sample (Figure 10.3). In adults, this variant has a poorer prognosis compared with L1 ALL based on the more frequent presence of the Philadelphia chromosome p190 variant (rather than p210, as with CML), with similar response rates but more rapid relapse and diminished long-term survival.18'33,48

L3—Burkitt lymphoma/leukemia, with small uniform lymphoid blasts characterized by vacuolated cytoplasm containing glycogen, and frequent mitotic figures denoting rapid growth (Figure 10.4).

Although classified as a form of ALL, the L3 (Burkitt) variant differs in many respects from other forms of ALL. L3 ALL presents in developed countries as an aggressive disease, often with intra-abdominal lymph

Figure 10.4 L3—Burkitt leukemia in bone marrow with uniform blast forms, cytoplasmic vacuoles, and increased mitoses

10.1 Estimated frequency of specific genotypes of ALL in children and adults

ALL genotype Children Adults

Hyperdiploidy >50 25 7


TEL/AML1 t(12;21)

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