French–American–British classification

French–American–British (FAB) classification is a system used to categorize the various types of leukemia, a group of blood disorders characterized by the overproduction of abnormal white blood cells. Developed in the 1970s through the collaborative efforts of French, American, and British hematologists, the FAB classification system was the first to standardize the terminology and diagnostic criteria for leukemia, facilitating more accurate diagnoses and enabling more effective communication among medical professionals worldwide.

Overview

The FAB classification system categorizes leukemia based on the morphology (shape and appearance) and cytochemistry (chemical characteristics) of the leukemic cells, as observed under a microscope. It primarily focuses on two major types of leukemia: Acute lymphoblastic leukemia (ALL) and Acute myeloid leukemia (AML). Each of these types is further subdivided into various subtypes, based on specific features of the leukemic cells.

Classification

Acute Lymphoblastic Leukemia (ALL)

The FAB classification divides ALL into three subtypes:

• L1: Small, uniform cells
• L2: Larger, more variable cells with heterogeneous nuclei
• L3: Large, uniform cells with vacuolated cytoplasm

Acute Myeloid Leukemia (AML)

AML is classified into eight subtypes, 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)
• M4: Acute myelomonocytic leukemia
• M5: Acute monocytic leukemia
• M6: Acute erythroid leukemia (erythroleukemia)
• M7: Acute megakaryoblastic leukemia

Significance

The FAB classification system has played a crucial role in the study and treatment of leukemia. By providing a common language for hematologists, it has facilitated international collaboration and research, leading to significant advancements in the understanding and management of these diseases. However, with the advent of more sophisticated diagnostic technologies, such as immunophenotyping and genetic testing, the FAB classification has been largely supplanted by the World Health Organization (WHO) classification system. The WHO system offers a more comprehensive classification that incorporates genetic, immunologic, and molecular features, providing a more accurate prognosis and guiding more targeted therapies.

Limitations

While the FAB classification was groundbreaking at its inception, it has several limitations:

• It relies heavily on the subjective interpretation of cell morphology, which can lead to inconsistencies in diagnosis.
• It does not incorporate genetic or molecular information, which are critical for understanding the behavior of leukemic cells and for guiding treatment decisions.

Current Status

Despite its limitations, the FAB classification remains a historical cornerstone in the field of hematology. It laid the groundwork for the development of the WHO classification, which is now the standard for diagnosing and classifying leukemia. The transition from the FAB to the WHO classification exemplifies the evolution of medical science, highlighting the importance of integrating new technologies and discoveries into clinical practice.