What is Acute Myeloid Leukemia (AML)?
Acute Myeloid Leukemia (AML) is a type of cancer that originates in the
bone marrow and affects the
myeloid line of blood cells. It involves the rapid proliferation of abnormal myeloblasts, which are immature white blood cells. These cells crowd out normal blood cells, leading to various clinical manifestations such as anemia, infection, and bleeding.
Histological Features of AML
Under the microscope, AML is characterized by an increased number of
myeloblasts in the bone marrow. These cells typically have large nuclei with immature chromatin and prominent nucleoli. The cytoplasm may contain
Auer rods, which are needle-like inclusions that serve as a hallmark for the diagnosis of AML.
Role of Bone Marrow Biopsy
A
bone marrow biopsy is crucial for diagnosing AML. The biopsy involves extracting a small sample of bone marrow tissue, which is then examined histologically. The presence of more than 20% myeloblasts in the bone marrow is a key diagnostic criterion for AML.
Immunohistochemistry in AML
Immunohistochemistry (IHC) is often employed to identify specific markers on the surface of cells. AML cells typically express markers such as
CD34,
CD117, and
MPO (myeloperoxidase). The presence of these markers helps in confirming the diagnosis and classifying the subtype of AML.
Genetic Abnormalities
Many cases of AML are associated with specific genetic abnormalities, which can be identified using techniques like
fluorescence in situ hybridization (FISH) and
polymerase chain reaction (PCR). Common genetic abnormalities include translocations such as t(8;21), inv(16), and t(15;17). These genetic markers not only aid in diagnosis but also have prognostic implications.
Histopathological Variants
AML can be classified into several subtypes based on histopathological features. The
French-American-British (FAB) classification system divides AML into eight subtypes (M0-M7) based on the morphology and maturation stage of the myeloid cells. For instance, M3 (acute promyelocytic leukemia) is characterized by the presence of abnormal promyelocytes.
Treatment and Prognosis
The treatment of AML typically involves chemotherapy, targeted therapy, and sometimes
stem cell transplantation. The histological and genetic features of the leukemia play a significant role in determining the treatment plan and prognosis. For example, patients with t(15;17) translocation generally have a better prognosis due to the effectiveness of targeted therapy with all-trans retinoic acid (ATRA).
Conclusion
Histology plays a pivotal role in the diagnosis, classification, and management of Acute Myeloid Leukemia. Through the examination of bone marrow biopsies, immunohistochemical staining, and genetic testing, pathologists can provide crucial information that guides the clinical approach to this aggressive form of leukemia.
