W5L10 - Approach to Acute Leukemia Flashcards
Acute Leukemia - Clinical
The clinical presentation is often non-specific
- usually reflects impairment of bone marrow haematopoiesis
- anaemia → pallor & fatigue
- thrombocytopenia → bruising & bleeding
- neutropenia → fever & infections
- may invade tissue and increase the size of the tissue
Patients with AML:
- WBC typically between 5.0 and 30.0 x 10^9/L
- may be as low as 1.0 or high as 200 x 10^9/L
Classification of Acute Leukemia
Classification requires the accurate identification of blast cell characteristics
Classification is complex & requires multiple techniques to achieve
Allows the most effective therapy to be used treat the patient
Allows understanding of the biology of the haematopoietic neoplastic to provide the patient with an accurate prognosis
WHO Classification of Haematopoietic Neoplasms
Acute myeloid leukemia (AML) and related neoplasms are considered sub-categories of ‘myeloid neoplasms and acute leukaemia’
- AML with recurrent genetic abnormalities
- AML with myelodysplasia-related changes
- therapy-related myeloid neoplasms
- AML, NOS
- myeloid sarcoma
- myeloid proliferations related to down syndrome
AML with Recurrent Genetic Abnormalities
If no previous treatment with chemotherapy or radiotherapy then detection of specific genetic abnormality defines the AML
Does not need to have 20% blasts for diagnosis of AML
AML Not Otherwise Specified (NOS)
Diagnosis of AML, NOS needs exclusion of other criteria
i.e.
- if no previous therapy ( chemotherapy or radiotherapy)
- if no recurrent genetic abnormalities
- if no myelodysplasia
Then => AML, NOS
Categories based on maturation of blast and the origin of the blast
- e.g. AML with minimal differentiation
- Acute monoblastic/monocytic leukemia
Acute Myeloid Leukemia
Initial recognition of acute leukaemia is typically based on FBC/PBS
- morphology
Classification of cell lineage/origin/biological behaviour is based on:
- cytochemistry
- immunophenotype
- cytogenetic & genetic analysis
May use haematopoietic cells obtained from the blood or bone marrow
Morphology of Blast Cells
Blast cells = poorly differentiated precursor haematopoietic cells
Blast morphology is highly variable
In general:
- large (15-30 µm diameter)
- high nuclear:cytoplasmic ratio
- nucleus often has folds or other irregularities
- fine-coarse chromatin
- nucleolus evident (often prominent)
- cytoplasm scant to abundant
- may have azurophilic cytoplasmic granules
- Auer rods may be present in some types
Phenotype cannot be determined from morphology
Morphology: Cytochemistry
Used to identify cellular constituents indicative of cell line
Myeloperoxidase (MPO)
- > 3% positive indicates myeloid origin
- lymphoid origin negative
Sudan black B (SBB)
- similar but less specific than MPO
Non-specific esterase (NSE)
- monoblasts > 80% positive
Chloroacetate esterase
- granulocytes positive
Staining intensity increases with maturity (differentiation)
Negative results may occur with poorly differentiated myeloid cells
Less commonly done in favour of immunophenotyping
Immunophenotyping
Immunophenotyping by flow cytometry is essential for the accurate diagnosis and classification of acute leukaemia and monitoring residual disease
CD45 is expressed in > 95% of cases of AML
HLA-DR is expressed in ~85% of cases
CD13 is expressed in 75-95% of cases
CD33 is expressed in 65-95% of cases
CD117 is expressed in ~70% of cases
CD34 is expressed in ~60% of cases
Expression of Cell-Surface and Cytoplasmic Markers
Precursors - CD13, CD33, CD34, CD117, HLA-DR
Granulocytic markers - CD65, cytoplasmic MPO
Monocytic markers - CD14, CD36, CD64
Megakaryocytic markers -CD41 (glycoprotein IIb/IIIa), CD61 (glycoprotein IIIa)
Erythroid markers - CD235a (glycophorin A), CD36
Cytogenetics
Crucial for diagnosis of AML with recurrent genetic abnormalities
Important for many other classification categories
Used to inform treatment, prognosis
Molecular Genetics of AML
23 genes have been found to be commonly mutated in AML with a further 237 mutated in some cases of AML
Mutated genes have been classified into 9 categories
9 Functional Categories of Mutated Genes in Molecular Genetics
- Transcription factor fusions
- NPM1 gene
- Tumour suppressor genes
- DNA methylation-related genes
- Signalling genes
- Chromatin-modifying genes
- Myeloid transcription factor genes
- Cohesin complex genes
- Spliceosome complex genes
Molecular Genetics - Recommendations for Diagnostic Investigations
Mutations in NPM1, CEBPA, and RUNX1 genes
- because they define disease categories
Mutations in FLT3
- for internal tandem duplications [ITDs] and tyrosine kinase domain (TKD) mutations at codons D835 and I836
- activating mutations of FLT3 are not only prognostic, but may beneficially be affected by tyrosine kinase inhibition treatment
Mutations in TP53 and ASXL1
- because they consistently have been associated with poor prognosis
Minimal Residual Disease
Small amounts of remaining neoplastic cells
Determined by
- RT-PCR detecting leukaemia specific targets
- flow cytometry detecting leukaemia associated phenotypes
Basis of MRD monitoring
- early assessment of response to therapy
- guide post remission therapy
- detect impending relapse & guide pre-emptive treatment
