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Acute megakaryoblastic leukemia
12nd Department of Internal Medicine, Christian-Albrechts-University of Kiel, Germany.
Abstract:
In 1985 acute megakaryoblastic leukemia was included in the FAB classification system of hematological neoplasias with the designation of AML M7. It occurs in all age groups with two peaks in distribution. The one is in adults and the other in children 1 to 3 years of age especially in those with Down's syndrome. The diagnosis of AML M7 requires more than 30% of the nucleated bone marrow cells being megakaryoblasts. The more common types of AML MO-M6 have to be excluded by morphological and cytochemical analysis whereas immunology is needed to exclude ALL. The megakaryocytic nature of the leukemia has to be proven by ultrastructural demonstration of platelet peroxidase or by immunological demonstration of CD61, CD42, CD41 on the surface of the leukemic blasts. Megakaryocytic/megakaryoblastic leukemias show a wide morphologic spectrum. In some instance small cells dominate, clearly showing megakaryocytic differentiation with scant amounts of cytoplasm and with nuclei showing dense chromatin. On the other hand, there are cases with larger cells resembling ALL-L2 blasts with moderate amounts of rather basophilic cytoplasm which in some instances contain azurophilic granules. Cytoplasmic blebs and protrusions are the most prominent feature of many cases. The nuclei of these cells are round with more finely reticulated chromatin and with prominent nucleoli. The megakaryoblastic nature of these cells can be suggested by morphology. However, according to our experience there are cases of c-ALL with the very same morphologic picture. Consequently, immunologic phenotyping of these cases is necessary in any instance. Cytochemistry is of limited diagnostic value in megakaryoblastic leukemias. Usually it is used to exclude the more common types of leukemia.
Insights
Acute megakaryoblastic leukemia (AML M7) diagnosis requires over 30% megakaryoblasts in bone marrow. Immunophenotyping is crucial to confirm AML M7 and differentiate it from other leukemias, as morphology alone can be misleading.
Area of Science:
- Hematology
- Oncology
- Cell Biology
Background:
- Acute megakaryoblastic leukemia (AML M7) is a subtype of acute myeloid leukemia.
- It affects all age groups, with notable peaks in adults and children aged 1-3, particularly those with Down's syndrome.
- Diagnosis requires over 30% megakaryoblasts in nucleated bone marrow cells.
Purpose of the Study:
- To outline the diagnostic criteria for AML M7.
- To emphasize the importance of immunophenotyping in differentiating AML M7 from other leukemias.
- To describe the morphological spectrum of megakaryoblastic leukemias.
Main Methods:
- Morphological and cytochemical analysis to exclude AML MO-M6.
- Immunological analysis (e.g., CD61, CD42, CD41) to confirm megakaryocytic lineage and exclude acute lymphoblastic leukemia (ALL).
- Ultrastructural demonstration of platelet peroxidase for diagnosis.
Main Results:
- AML M7 diagnosis is confirmed by >30% megakaryoblasts.
- Morphological features can be variable, ranging from small to large cells with distinct cytoplasmic and nuclear characteristics.
- Immunophenotyping is essential as morphology can mimic other conditions like common acute lymphoblastic leukemia (c-ALL).
Conclusions:
- Accurate diagnosis of AML M7 relies on a combination of morphology, cytochemistry, and crucially, immunophenotyping.
- Cytochemistry has limited value for definitive AML M7 diagnosis but aids in excluding other AML subtypes.
- Immunological markers are indispensable for confirming megakaryocytic differentiation and distinguishing AML M7 from morphologically similar leukemias.