FAB Classification Flashcards

Study Notes

FAB Classification: Key Definitions and Characteristics

M0: Represents blasts with minimal maturation. High N:C ratio, size similar to segs, nuclei are round or oval and eccentric.
M1: Lacks maturation. Auer rods present; cells exhibit more maturity with promyelocytes and potentially mature segs.
M2: Displays maturation with presence of myelocytes and metamyelocytes. Possible eosinophils (eos) and typically dysplastic maturing cells. Agranular blasts may have nucleoli and clumpy chromatin.
M2 Eo: Features mild atypia with coarse cytoplasmic granules seen in immature eos; mature eos are usually not atypical.
M2Ba (Acute Basophilic Leukemia): Characterized by mature cells with coarse basophilic granules. Cytoplasm shows basophilia and possible vacuoles, with frequent dysplastic features.
M3 (Promyelocytic Leukemia): Presence of dysplastic clonal cells resembling segs. Cytoplasm ranges from light blue to pink with abundant granules, Auer rods, and coarsely clumped chromatin. Associated with Disseminated Intravascular Coagulation (DIC).
M3 Hypergranular: Commonly shows frequent Auer rods and granules, including giant granules.
M3v: Displays limited granules, usually lacking Auer rods, but has a high peripheral blood blast count.
M4 (Naegeli's Acute Monocytic Leukemia): A myelomonocytic classification originating from progenitor stem cells. Myeloblasts are typically cytoplasm-poor, with potential Auer rods, variable N:C, and nucleoli in most immature cells.
M4Eo: An extension of M4 that includes a significant eosinophil presence, sometimes exceeding 50% in bone marrow.
M5a (Monoblastic Leukemia): Predominantly monoblasts (≥80% in bone marrow) with abundant cytoplasm and few granules. Auer rods absent, prominent vacuoles and fine chromatin with nucleoli.
M5b: Displays a wider variability in cell size and shape than M5a. Cytoplasm can be light blue to gray with prominent vacuoles and more clumped chromatin, leading to increased organomegaly.
M6 (diGuglielmo Syndrome): Characterized by erythroleukemia, marked dysplastic proerythroblasts. Contains multilobulated nuclei and Howell-Jolly bodies, demonstrating nuclear asynchrony and potential transformation to other leukemias over time.
M6a: A mix of proerythroblasts and myeloblasts.
M6b: Composed solely of proerythroblasts.
M7 (Megakaryoblastic Leukemia): Involves proliferation of megakaryoblasts and atypical megakaryocytes, leading to dry bone marrow taps; at least 20% of bone marrow cells are megakaryoblasts.

Staining Characteristics for FAB Classes

MPO Stains:
- M0: MPO- SBB- NSE- TdT+ SE-
- M1: MPO+ SBB+ NSE- TdT+ SE+
- M2: MPO+ SBB+ NSE- TdT +,- SE+
- M3: MPO+ SBB+ SE+ NSE- TdT-
- M4: MPO+ NSE+ SE+ TdT- (often targets skin and gums)
- M5a: MPO- SBB- NSE+
- M5b: SBB+/-, NSE+
- M6: PAS+; iron stain shows ringed sideroblasts; Prussian blue+
Specific Stains:
- Myeloperoxidase (MPO): Stains primary granules of myeloid cells, identifying late myeloblasts to segs (positive), and faint positivity in monoblasts to monocytes.
- Sudan Black B (SBB): Targets phospholipids in granules. Like MPO, identifies late myeloblasts to segs, with faint positivity for monoblasts.
- Specific Esterase: Stains enzyme in primary granules, confirming myeloid cell lineages.

Clinical Relevance

Understanding FAB classification and staining characteristics aids in diagnosing various forms of acute myeloid leukemia (AML). Each subtype provides insight into cellular morphology and expected disease progression.

Description

Test your knowledge on the FAB classification system through these flashcards. Each card details the characteristics of different types of leukemias, including M0, M1, and M2 classifications. Perfect for students in medical or health sciences.