French-American-British (FAB) Classification of ALL

FAB Subtype Approximate % of Adult ALL Patients Immunologic Type Comments
L1 30% T cell or pre-B cell  
L2 65% T cell or pre-B cell  
L3 5% B cell Poor prognosis with standard therapy. Also called Burkitt leukemia.

This system has largely been replaced, as new lab tests now allow physicians to classify ALL more accurately.