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Melanoma Pathology,
Treatment and Genetics
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Key Issues
Incidence
What is melanoma?
Pathology
Pathology/Aetiology of Skin cancer.
Causes
Who gets it
Location of melanomas (what part of body) Role of UV radiation
Treatment of Melanoma
Melanoma Associated genes
Tumour suppressor genes Oncogenes
Antigenicity of Melanomas.
A genetic model of melanoma.
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Incidence of Melanoma
Skin cancer is the second most common cancer in theUK.
About 50,000 cases per year in the UK (includes SCC& BCC)
5-6000 are melanoma
1 in 80 people in the US/Australia get CMM
1 in 200-250 in the UK get CMM
CMM is responsible for 90% of skin cancer associateddeaths
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Cutaneous MalignantMelanoma
CMMs are derived from the melanocytes located inthe basal layer of the epidermis.
Very aggressive tumour and metastasise to a varietyof organs
Bone
Brain
Juxtaposed lymph nodes
Two modes of growth Radial growth phase over surface of skin
Vertical growth phase into lower layers prior tometastasis
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Skin Anatomy
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Melanoma Types
Lentigo MM Superficial Spreading MM
Acral MM Nodular MM
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Melanoma Pathology
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Cutaneous MalignantMelanoma
If tumour resected before a vertical invasion of lessthan 3mm - associated with a cure.
Greater than 3mm metastatic disease likely.
80% of CMM patients get metastatic disease.
Metastatic lesions associated with about 6 months
survival following diagnosis.
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Local Spreading of Melanoma
Point of origin: Acquired/dysplastic neavus (mole)
Radial Growth Phase
Vertical g
rowthphase
Malignant
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What Causes Melanoma
Strong evidence that melanoma occurs on sundamaged skin.
High risk associated with short bursts of intense UVexposure. Intermittent exposure during childhood - important factor.
Who gets it
Those with high number of naevae (moles).
Type 1 skin blue eyes, blond, burn easily, thosewith a family history of melanoma.
Age group: 40 60 year olds, but can occur at any age(rarely in children)
More women than men get melanoma.
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Pathology/Aetiology ofSkin Cancer
SCC BCC CMM
Sun Sensitive skin Total Sun Exposure Childhood Sun
Exposure
Intermittent Over
Exposure
P53 Mutation
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Location
Affect most parts of the body.
Women legs.
Men trunk especially the back.
Role of Sunlight (UV irradiation)
UVA: 320 400nm
UVB: 280 320nm
UVC: 100 280nm
All UVC and some UVB is blocked by atmospheric ozone.
UVB causes the erythemal response reddening associated with sunburn.
UVA: Skin ageing
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Treatment of Melanoma
If melanoma is detected early:
Surgical resection of primary tumour followed bycareful monitoring.
Advanced Disease Resection of Primary tumour
Lymph node excision and surgical removal ofmetastases where possible
High dose interferon to treat disseminated
disease (boost immune system) Melphalan + Interferon
Prognosis is poor with advanced disease
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Experimental Models
Xiphophorus fish: Irradiation with single dose UVBinduces melanoma in fish (Setlow). Spectral regions contributing to melanoma: a personal view.
Setlow RB, J Investig Dermatol Symp Proc. 1999 Sep;4(1):46-9
XPA transgenic mice: Knockout mice (excision repairgene XPA) are susceptible to melanoma induction byUVB irradiation
Photocarcinogenesis: UVA vs UVB.de Gruijl FR.Methods Enzymol. 2000;319:359-66.
Aim is to produce anAction Spectrum in humansDetermination of what UV wavelength is responsiblefor CMM induction.
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Molecular Genetics of
Melanoma
A number of chromosomal aberrations are knownto accumulate during CMM development.
Principally non-random Losses of Heterozygosity(LOH) (remember Knudsons two hit hypothesis ofretinoblastoma)
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LOH in Melanoma
Chromosome Frequency of LOH
1p36 25%
6q22-24 30-35%
9p21 (p16) 50-60%
10q22-25 30%
11q23-ter 25%
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Tumour Suppressor Genes
No evidence of P53 involvement in melanoma development.
CDKN2A/INK4A/P16: Cyclin dependent kinase 4 inhibitor.
Causes a G1 arrest by inhibiting the phosphorylation of RB.Inhibits the action of cyclin dependent kinases 4 and 6.
Gene Structure:
3 exons
Exon 1: 150bp (50aa)
Exon 2: 307bp (101aa)
Exon 3:12bp (3 aa)
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Cell Cycle Control(abbrev.)
G1 S G2 M
G0
CyclinD1
CyclinD2
CyclinD3
CDK4
CDK6
p15,p16, p18, p19
pRB
CDK2 CDK2 CDK1
Cyclin BCyclin E Cyclin A
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Exon 1 Exon 2 Exon 1 Exon 1 Exon 2 Exon 3
Exon 1 Exon 2
Exon 1 Exon 2 Exon 3
Exon 1 Exon 2 Exon 3
The INK4 locus of chromosome 9p21
p15
p16
p14 ARF
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Inactivation of P16
Deletion: About 50-60% of melanomas display LOH atchromosome 9p21 (location of P16).
P16 loss is thought to be a critical event in
melanogenesis.
Methylation: CpG islands in the promoter region ofP16. Causes functional silencing of the gene.
Occurs frequently in head and neck (SCC), breast,prostate, bladder cancers.
Probably a significant event in melanoma development
Point mutation: Observed in many cancers includingmelanomas
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Point mutations in P16
Inactivation of P16 by point mutations nota resultof prior exposure to UV irradiation.
UV exposure = pyrimidine dimers in DNA.
Mutation by UV = CCTT tandem base substitution. Never observed in any known melanoma tumour
suppressor gene.
Despite the obvious role of UV in melanogenesis.
Mutation of P16 in the germline of melanomakindreds establishes P16 as a familial TSG.
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Pyrimidine Dimer
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Other Melanoma Tumour SuppressorGenes
PTEN: Phosphatase and Tensin homologue.
also called
MMAC1: Mutated in Multiple Advanced Cancers.
Encodes a tyrosine phosphatase with extensive homology
to the cytoskeletal proteins auxillin and tensin. Suppresses Akt signalling
PTEN/MMAC1 maps to chromosome 10q23.3
9 exons
ORF: 1212nt
403 amino acids 47kDa
Functions as a negative regulator of signal transduction
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Any Other Melanoma TumourSuppressors?
KiSS1 Tumour suppressor Gene Chromosome 1p32
Regulates an antimetastasis gene onchromosome 6.
Associated with LOH on chromosome 6q16
LOH also demonstrated on
chromosomes 11
chromosome 10 (not PTEN)
As yet most of the tumour suppressor genes havenot been fully identified.
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Oncogene Activation and Melanoma
N-RAS mutational activation at codon 61
CAAAAA Destroys natural ATPase activity of Ras protein.
Observed in
Congenital naevi
Dysplastic naevi
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Oncogenes
B-Rafoncogenes: Ras-Raf MAP kinase signaltransduction pathway.
A serine threonine kinase leading to
upregulation of BRN-2 transcription factor
Mutations in 60% of primary melanomas
Elevated kinase activity Capable of transforming NIH3T3 cells in
culture.
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Other Potential Melanoma AssociatedGenes
Integrins
A diverse family of receptors that mediate adhesionbetween the cell membrane and the extracellular matrix.
Composed of and subunits. Combinations of 14 and 8 subunits comprise a
family of over 20 integrin types.
Certain classes of integrin expression has been shown tobe upregulated during transition from radial to verticalgrowth phase.
Integrin v
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Antigenicity of Melanomas
Melanomas are thought to have an antigenic
component Photo-immunological aspects of melanoma.J.Investigative Dermatology. 24: 153-165(1995) Kripke ML et al.
May render them sensitive to immunologicalmethods of treatment.
High molecular weight melanoma associatedantigen: associated with many melanomas
Possible exploitation for immunotherapy.
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A Genetic Model
Normal melanocyte Dysplastic or
acquired naevus
Radial
growth phase
Vertical
growth phase
Metastatic
Melanoma
N-Ras Chromosome 9
P16/other TSGs
Chromosomes 6
and 11
Integrins? Chromosome 1(KiSS 1)
and 10 (PTEN/MMAC1)
B-Raf
Chromosome 7q34
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Summary
Incidence
What is melanoma?
Pathology
Pathology/Aetiology of Skin cancer.
Causes
Who gets it
Location of melanomas (what part of body) Role of UV radiation
Treatment of Melanoma
Melanoma Associated genes
Tumour suppressor genes Oncogenes
Antigenicity of Melanomas.
A genetic model of melanoma.