French-American-British (FAB) classification

A system that is used to describe and classify acute leukemias based on the cell line in which they develop (lymphocytic or myelogenous), as well as the microscopic features and chemical makeup of the blast cells (immature blood cells).

The FAB classification system divides acute lymphocytic leukemia into 3 types (L1, L2 and L3) and acute myelogenous leukemia into 7 types (M0 through M7).