| 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.