Staging
FAB classification of acute lymphoblastic leukemia
The historical French-American-British system classifies acute lymphoblastic leukemia by blast morphology into L1, L2, and L3 categories.
Also called: FAB scheme
Stages
- L1
L1
Small, relatively uniform blasts with scant cytoplasm, regular nuclei, condensed chromatin, and inconspicuous nucleoli.
- L2
L2
Blasts variable in size, with irregular nuclei, heterogeneous lacy chromatin, and more plentiful, weakly basophilic cytoplasm.
- L3
L3
Large, relatively uniform blasts with stippled chromatin, prominent nucleoli, and intensely basophilic, vacuolated cytoplasm.
Judged onMorphology of leukemic blasts
FAB morphology was historically used to divide acute lymphoblastic leukemia into three categories. It describes visible differences among lymphoblasts, including cell size and uniformity, nuclear appearance, chromatin, and cytoplasm. The system is now mainly of historical value; contemporary classification uses immunophenotypic and genetic information.