15. Haematological Malignancies Flashcards
haematological malignancies
Clonal diseases -cells affected share a unique mutation theyre clones of that cell
Cell: undergone genetic changes (somatic mutation) leading to malignant transformation. Mutation is not inherited; it is a mutation that has been acquired by the cell
Excessive proliferation
Resistance to apoptosis
Clonal diseases: derived from a single cell that has undergone genetic alteration
overtime the % of bone marrow cell population would be less normal haemopoietic tissue and more malignant cells after mutation, especially after clonal expansion when they become the majority of cells within the bone marrow
pathogenesisi of haematological malignancy
Cause:
- environment
- toxin
- virus infection
- drug
- genetic disposition
To pathogenesis, altered gene expression
- oncogene
- tumour suppression gene
To: translocation mutation amplification deletion
showing the phenotype
- decreased apoptosis
- increased proliferation
- decreased differentiation (don’t become a mature cell)
(clone of malignant cells)
what causes malignancy
number of factors
usually a combination of genetic predisposition and environmental factors including: Infection Ionizing radiation Chemicals Drugs
genetic predisposition causing malignancy
Genetic predisposition:
Downs syndrome - increased incidence of leukaemia [acute].
infection causing malignancy
Infection:
Viruses:
human T-lymphotropic virus type 1 (HTLV-1) - adult T-cell leukaemia/lymphoma (ATLL). HTLV Increased risk of developing lymphoma or leukemia – involves the cell that was involved in the initial infection. T cells infected by virus, leukemia associated is a t cell leukemia or lymphoma
Epstein-Barr virus – leaves person at risk of Burkitt’s lymphoma
Bacteria:
Helicobacter pylori infection - gastric lymphomas. GI tract
infection causing malignancy - ALL (acute lymphoblastic anemia)
Proportion of childhood ALL:
initiated by genetic mutations that occur during development in utero
? Environmental exposure during pregnancy
2nd transforming event within tumour cell after birth ie needs to develop second mutation. Two hit hypothesis
? Abnormal response of immune system to infection, unclear mechanism
Children for e.g. in nursery daycare
decreased incidence of ALL in comparison to those living in more isolated communities with decreased exposure to common infections in early years
Twin studies – both may be born with same chromosomal abnormality happened in utero
Second transforming event: different for both twins, one develops ALL at ~5, other remains well until 14 (Wiemals JL et al. Blood (1999):1057-62
ionising radiation causing malignancy
causes mutations
increases risk of malignancy - Hiroshima and Nagasaki following atomic bomb blasts
chemicals causing malignncy
Benzene (chronic) in cig smoke - chromosomal abnormalities in leukaemia
drugs cuasing malignancy
Drugs:
Alkalyting agents, e.g.chlorambucil - myeloid leukaemia.
Chlorambucil is a treatment for cancer, myeloid leukemia. But cann affect other cells and cuse malignancies also
mechanism of malignancy
Dysregulation of genes involved in:
- proliferation, differentiation and cell survival
- Leads to altered signalling pathways
These abnormal genes are known as:
- oncogene (normal partners: “proto-oncogenes“)
- Tumour supressor genes
oncogenes
Derived from proto-oncogenes
Gain of function mutation
-amplification, point mutations or chromosomal translocations
Uncontrolled proliferation
Blockage of differentiation or
Prevention of apoptosis
overproduction of immature cells that wont die
the dual nature of oncogenes
normal protooncogene has essential cellular functions
A transforming oncogene becomes a cellular oncogene to altered cellular functions to spontaneous neoplasm
tumour suppressor genes (TSG)
Commonly involved in cell-cycle
Inactivation of a tumour-suppressor gene:
- by deletion or mutation
- loss of function mutations
- promotes malignant transformation
Encode for proteins that negatively regulate proliferation
p53 most significant TSG in human cancers (~50% of malignant disease)
here, they lose a function
Proliferation of normal cells depends on
balance between proto-oncogenes and tumour suppressor genes
if protooncogene and TSG balanced, leads to regulated proliferation and apoptosis
however if eg radiation virus mutation, and no TSG, and only oncogenes we get malignant cells with excess proliferation and failure of apoptosis
Genetic abnormalities associated with Haematological Malignancies
Point mutations
Gene and chromosomal deletions
Chromosomal duplication (e.g. trisomy 12 in CLL) or gene amplification (not common)
Frequent genetic abnormalities in leukaemia and lymphoma
myeloid AML M3 (subclass cell type) disease, genetic abnormality at t (15;17) (translocation), involving the oncogenes RARalpha and PML
myeloid CML disease genetic abnormalilty at t (9;22) and oncogene involved is ABL, BCR
lymphoid disease follicular lymphoma genetic abnormality is at t (14;18) and oncogene involved is BCL-2 to IgH
The role of / detection of genetic markers
3 main roles in haematological malignancies:
- Initial diagnosis
- Sub-classification using genetic markers
- Monitoring minimal residual disease to make sure no malignant cells within their circulation
- diagnosis of haematological malignancies
blood tests, symptoms are usually not specifc to a particular disease, we need to know where translocation is and whether it is of B or T cell
Genetic abnormalities [e.g. t(15; 17) or t(9; 22)]:
- specific for a particular disease
- determine the diagnosis
Clonal immunoglobulin or T cell receptor (TCR) rearrangements:
- determine clonality
- establishing if malignancy is of either B or T cell lineage.
- sub classification of haematological malignancy
presence of a particular translocation
t(14;18) in diffuse-large B cell lymphoma
prognostic information for this group of patients
- monitoring minimal residual disease:
Minimal residual disease (MRD):
Low level of disease detectable using available methods
Diagnosis:
possible that patient will have approximately 1013-1014 malignant cells.
After treatment (trying to reach MRD):
patient is described as being in remission when less than 5% of blasts detected in the marrow.
Can equate to 108-1010 blasts still remaining
usually below the detection limit of conventional techniques.
need sensitive techniques to detect malignant cell in large population of other cells to show treatment is effective
- Monitoring minimal residual disease (cont’d)
Molecular techniques, PCR capable of detecting 1 malignant cell in up to 106 normal cells
Translocations: disease specific and are therefore very useful for MRD monitoring.
Presence of MRD: provides a high risk of relapse allowing the potential of additional therapy prior to relapse.
MRD not detected: risk of relapse is low allowing the potential reduction in treatment
minimal residuall disease
Treatment – remission. Theyre not cured, require further treatment to maintain remission and ensure all malignant cells are being affected and continuing treatment all the way down to look at cure
But can relapse – disease specific and what equipment is available
decreasing curve, remission decreases no of malignant cells to MRD, continues to cure or relapses
Assessment of malignant cellsLab techniques
Includes: Karyotype analysis Fluorescent in situ hybridization analysis Southern blot analysis Polymerase chain reaction
Assessment of malignant cells
karyotype analysis
-Karyotype analysis
Morphological analysis of chromosomes from tumour cells under the microscope
Each chromosome pair shows an individual colour pattern. look for changes
Assessment of malignant cells - fluorescent in situ hybridisation
-Fluorescent in situ hybridisation
fluorescent-labelled probes bind to specific parts of genome
detect extra copies of genetic material
presence of chromosomal translocations
Assessment of malignant cells southern blot analysis
-Time consuming, relatively insensitive but still used
Extract DNA from leukaemic cells,
restriction enzyme digestion,
gel electrophoresis and
transfer by “blotting” to a suitable membrane
-If translocation has occurred, novel band of different electrophoretic mobility is seen
Assessment of malignant cells - polymerase chain reaction
amplify a DNA segment, then sequenced
detect chromosomal translocations
determine the presence of clonal cells in B and T cell malignancies
WHO Classification of Haematological Malignancy
Various systems used for classification, for e.g.-
- World Health Organization (WHO) classification of haematopoietic and lymphoid neoplasms began in 1995.
- Based on the REAL (Revised European-American classification of lymphoid neoplasms).
- WHO classification: morphology and genetic features.
- The leukaemia classification uses the French-American-British (FAB) classification but also includes molecular genetics.
initial classification of haematological malignancies
Haematological malignancies were primarily classified according to lineage Myeloid Lymphoid Histiocytic/dendritic Mast Cell
Categories then defined by use of: morphology immunophenotype genetic features Clinical syndromes
Classification of haematological malignancy
Lymphoid/Myeloid: acute and chronic
eg lymphoid
Acute Lymphoblastic Leukaemia ALL and subtypes
Chronic lymphocytic leukaemia
eg myeloid
Acute myeloid leukaemia (AML) and subtypes
Chronic myeloid leukaemia (CML)
