Lecture 14: Cytogenetics of Cancer Flashcards
Semantics;
definition of ‘mosaic’
an art of decoration
with small pieces of coloured glass, stone or other materials
Definition of genetic mosaicism
Mosaicism -
- presence of TWO OR MORE CELL POPULATIONS (I),
- each with its “PERSONAL” genome, in
- an individual DEVELOPED FROM A SINGLE FERTILISED EGG (II)
How is genetic mosaicism DISTINGUISHED FROM CHIMERA?
EXAMPLES? 2
- Distinguish from chimera – TWO OR MORE CELL POPULATIONS (I)….’DERIVED FROM DISTINCT FERTILISED EGGS’ (III)
e.g.
– fusion of DZ twins
– transplantation
Acquiring mosaicism…ERRORS OCCURRING IN: 3
1 – Stem cells (body-wide mosaicism)
2 – Differentiating cells (tissue-specific)
3 – Differentiated cells (organ-specific)
Distribution of mosaicism…
‘as seen on diagram slide 6’
= 3
- a) somatic
- b) somatic + germline
- c) germline (gonadal)
MOLECULAR CLASSES of DISEASE ASSOCIATED mosaicism = 5
1 * Mendelian ( point mutations/small indels)
2 * Chromosomal / CNV
3 * Epigenetic (imprinting)
4 * Mitochondrial – heteroplasmy
5 * Complex - combination of different molecular classes
Health impact of mosaicism = 3
1 * Non-pathogenic
– X-chromosome inactivation
– Immunogenetic mosaicism
– Complexity of neuronal cell types (somatic retrotransposition)
2 * Pathogenic
– Disorders exclusively associated with mosaicism, i.e. Pallister-Killian syndrome
3 – Cancer
Health impact of mosaicism: NON-PATHOGENIC…3
- Non-pathogenic
1 – X-chromosome inactivation
2 – Immunogenetic mosaicism
3 – Complexity of neuronal cell types (somatic
retrotransposition)
Health impact of mosaicism: PATHOGENIC
– Disorders exclusively associated with mosaicism, i.e. Pallister-Killian syndrome
UNDERSTANDING Cancer cytogenomics: 4
1 * Key element for diagnosis (many subtypes of cancer may be distinguished based on underlying abnormalities)
2 * Prognostic value
3 * Detection of a specific abnormality may define
response to therapy
4 * Monitoring for an early detection of disease
relapse or cancer evolution including new abnormalities
Cytogenomic mechanisms of cancer
1 * ‘Chimeric gene fusion with oncogenic properties’
- (balanced structural chromosomal rearrangements)
2 * ‘De-regulated oncogene expression’
– Juxta-positioning in the vicinity of an enhancer
(structural rearrangements)
– Amplification (numerical or unbalanced structural
changes)
3 * ‘Tumour-suppressor gene inactivation’
- (numerical or balanced/unbalanced structural changes)
Cytogenomic mechanisms of cancer
‘Chimeric gene fusion with oncogenic properties’
(balanced structural chromosomal rearrangements)
Cytogenomic mechanisms of cancer:
‘De-regulated oncogene expression’ 2
1 – Juxta-positioning in the vicinity of an enhancer
(structural rearrangements)
2 – Amplification (numerical or unbalanced structural
changes)
Cytogenomic mechanisms of cancer:
‘Tumour suppressor gene inactivation’
Tumour-suppressor gene inactivation
- (numerical or balanced/unbalanced structural changes)
Gene fusion:
“Philadelphia” chromosome (Ph’)
(in haematological malignancies)
- Balanced translocation
- aberrant activation of cell signalling
– t(9;22) = chromosome 9 and 22 translocation
– BCR-ABL1 mRNA
– BCR-ABL1 protein
– Activation of downstream pathways
DIAGRAM ON SLIDE 11
Clinical implications of Ph
Ph’ = Philadelphia chromosome
- Chronic Myelogenous Leukaemia (CML)
- Acute Lymphoblastic Leukaemia (ALL)
Clinical implications of Ph’
— Chronic Myelogenous Leukaemia (CML)? = 3
- Increased incidence >50 years of age
- 95% Ph’+ve
- Good prognosis if Ph’+
Clinical implications of Ph’:
Acute Lymphoblastic Leukaemia (ALL) = 3
- 30% of adult ALL Ph’+ve
- 6% of child ALL Ph’+ve
- Poor prognosis if Ph’+ve
Ph’ BCR-ABL1 fusion(s)
SLIDE 13
BCR = m-bcr minor, M-bcr major, micro-bcr micro
– CHROMOSOME 22q11
ABL = frequent Abl breakpoints
CHROMOSOME9q34
COMMON IN ALL e1a2 transcript, p190
Common in CML p210
- e13a2 (b2a2)
-e14a2 (b3a2) transcripts
e19a2 transcript ..p230
neutrophils increase
thrombocytes increase
IMPORTANT DIAGRAM
Ph’ detection by FISH:
‘Major’ BCR breakpoint
UNDERSTAND DIAGRAM ON SLIDE 14
9q34 region = 671kb
- ASS1 …Exon 1b…Exon 1a… Exon 2 ..Exon 11
22q11 region = 287 kb
- exon 1 ….mbor region …exon 2 …exon 3 …m-bor region …3’
Ph’ detection by FISH:
‘Minor’ BCR breakpoint…
UNDERSTAND DIAGRAM ON SLIDE 15
9q34 region = 671kb
- ASS1 …Exon 1b…Exon 1a… Exon 2 ..Exon 11
22q11 region = 287 kb
- exon 1 ….mbor region …exon 2 …exon 3 …m-bor region …3’
Ph’-specific therapy?
Nucleus = chr 22, and chr 9 …translocation …philadelphia chro, with BCR-ABL
Cytoplasm = BCR-ABL PROTEIN
- ‘Tyrosine kinase inhibitors’
- DOWNSTREAM ACTIVATION
- Inhibitors of downstream signalling pathways
…
JAK/STAT
PI3K/AKT
RAS/MEK
mTOR
Src Kinases
DIAGRAM ON SLIDE 16
Cytogenomic abnormalities in the monitoring of disease progression…
important diagram on slide 17
Heamatological response
CHR
Cytogenetic response
CCyR
Molecular response
MMR (MR^3)
MR^4
MR^4-5
MR^5
?
the above list goes down these scales…
- Log reduction 0-6..
- BCR-ABL1% level…100%- 0.00001%
- Leukaemia cells
10^13 ….to 10^6…0
CHR, complete
haematological response; CCyR, complete cytogenetic response; MMR, major molecular response;
MR, molecular response with the number indicating log-reduction on the International Scale (IS)
Oncogene juxta-positioning to an enhancer
- Burkitt lymphoma (bone marrow)
- MYC (8q24) (from;)
- IGH (14q32)… chr 8 and 14 translocation t(8;14)
- IGK (2p12)… chr 2 and chr 8 translocation t(2;8)
- IGL (22q11)… chr 8 and chr 22 translocation t(8;22)
diagram on slide 18..important
Immunoglobulin gene enhancer-upregulated ‘MYC’ expression
Aberrant activation of a transcription factor
-t(8;14)
- MYC
- MYC mRNA
- MYC protein
- Aberrant expression of MYC target genes
diagram on slide 19
Oncogene amplification
Duplication:
MYCN (2p24.3)
—> ‘Double minutes’
and/or
—> ‘homogeneously stained region’
(diagram 20: no abnormality vs homogeneously stained region’)
then
‘NEUROBLASTOMA: most common solid tumour in children’
Tumour-suppressor inactivation:
RETINOBLASTOMA
- due to RB1 (13q14.2)
chr 13, del(13)
RB- functional allele
rb - mutated allele
Germline = 1st rb + RB –> CONSITUTIONAL = RB rb —> 2nd —> TUMOR = rb rb
LOOK AT DIAGRAM ON SLIDE 21
GERMLINE, CONSITUTIONAL, TUMOR
2 OTHER WAYS
The master catastrophic event in cancer: chromothripsis
- unperturbed chromosome
…. - CHROMOSOME SHATTERING
…. - CHROMOSOME REASSEMBLY
…. - TRUNCATED REARRANGED CHROMSOMES
= CAN LEAD TO
1. Double minutes
2. deletion
or ‘GENE CHANGE OF FUNCTION DUE TO’
3. fusion
4. disruption
DIAGRAM ON SLIDE 22
Chromothripsis is detected by genomic technologies
(SNP microarray and/or whole genome sequencing)
- CHR 14
- no copy number change
- rearrangment links for changes: GAIN, LOSS, INVERSION
- GLIOBLASTOMA:
MOST COMMON MALIGNANT BRAIN TUMOUR IN ADULTS
DIAGRAM ON SLIDE 23
Epigenetic defects and cancer:
gestational trophoblastic disease
GESTATIONAL TROPHOBLASTIC DISEASE (GTD)
- malignant
- premaligant
DIAGRAM ON SLIDE 24 ..FLOW CHART
Partial moles: diandric triplody
Partial moles: diandric triplody
- 18x3, XYY
- 13x3, 21x3
pathology outlines..partial hydatidiform mole
Special cases - 2 cases
- CHROMOSOME INSTABILITY
- leads to DNA-REPAIR DISORDERS
- ‘breaks and chromatid interchange’
= FANCONI ANAEMIA - REPLICATION DISORDERS
- patient vs control diagram slide 26
= BLOOM SYNDROME
- Cancer is associates with …..?
- MECHANSIMS?
- Challenges?
- detection of…provide clues for…
1 * Cancer is associates with somatic mosaicism and cytogenomic abnormalities
2 * Various underlying mechanisms
3 * Diagnostic challenges
4 * Detection of ‘cytogenomic abnormalities’ in
cancer provides clues for: ‘Dx, prognosis, therapy and disease evolution’
