FAB

French-American-British (FAB) classification is a system used to classify leukemia, a type of cancer that affects the blood and bone marrow. Developed in the 1970s by a group of French, American, and British hematologists, the FAB classification was the first successful attempt to categorize leukemia based on the morphology (appearance) and behavior of the leukemic cells as seen under a microscope. This classification system has played a crucial role in diagnosing and treating leukemia, although it has been largely supplanted by the World Health Organization (WHO) classification system, which also takes into account genetic and molecular features of the cancer cells.

Overview

Leukemia is broadly categorized into acute and chronic forms, which are then further divided into lymphocytic or myeloid, depending on the type of white blood cell they originate from. The FAB classification specifically categorizes acute leukemia, which includes Acute Lymphoblastic Leukemia (ALL) and Acute Myeloid Leukemia (AML).

Acute Lymphoblastic Leukemia (ALL)

In the FAB classification, ALL is divided into three subtypes based on the appearance of the lymphoblasts:

• L1: Small, uniform cells
• L2: Larger, more variable cells with more evident cytoplasm
• L3: Large, uniform cells with vacuolated cytoplasm, often associated with the Burkitt's lymphoma subtype

Acute Myeloid Leukemia (AML)

AML is classified into eight subtypes in the FAB system, from M0 to M7, based on the type of cell from which the leukemia develops and its level of maturity:

• M0: Undifferentiated acute myeloblastic leukemia
• M1: Acute myeloblastic leukemia with minimal maturation
• M2: Acute myeloblastic leukemia with maturation
• M3: Acute promyelocytic leukemia (APL), associated with a specific chromosomal translocation
• M4: Acute myelomonocytic leukemia
• M5: Acute monocytic leukemia
• M6: Acute erythroleukemia
• M7: Acute megakaryoblastic leukemia

Significance

The FAB classification was significant for several reasons. It provided a standardized language for hematologists worldwide, facilitating communication and research. It also helped in predicting the prognosis of patients and in guiding treatment decisions. For example, patients with AML M3 (acute promyelocytic leukemia) typically respond well to a treatment regimen that includes all-trans retinoic acid (ATRA), a differentiation therapy.

Limitations and Advancements

While the FAB classification was a major step forward, it has limitations. It relies solely on morphological characteristics, ignoring genetic, immunophenotypic, and molecular features that have been found to be crucial in understanding leukemia. The WHO classification system, which incorporates these additional characteristics, provides a more accurate diagnosis and prognosis and has largely replaced the FAB system.

Conclusion

The French-American-British (FAB) classification system was a pioneering effort in the classification of leukemia and laid the groundwork for the more comprehensive WHO classification system. Despite being less commonly used today, its development marked a significant milestone in the field of hematology.