Skin Cancer Flashcards
State five factors that portray the impact of skin cancer on the population
- size of problem
- demographic/behavioural
- cost of the problem
- morbidity & mortality
- lack of effective therapy
Name three types of skin cancer
Melanoma, squamous cell carcinoma, basal cell carcinoma
State four key risk factors for skin cancer
- Sun exposure
- Genetic susceptibility
- Immunosuppression
- Environmental factors
What conditions make a person more susceptible to skin cancer?
- DNA repair syndromes
- Albinism
- Naevoid basal cell carcinoma (Gorlin’s)
- Epidermolysis Bullosa (butterfly disease)
- Collagen deficiency
Give an example of a DNA repair syndrome that is a risk factor for skin cancer
Xeroderma Pigmentosum
What patient groups are at increased risk of skin cancer?
Organ transplant recipients
Haematological malignancy
Specific drugs
HIV/AIDs
What environmental factors lead to an increased risk of skin cancer?
Ionising radiation
Arsenic, coal tar
Trauma, chronic wound
How does a skin cancer arise due to genetics?
Cancers originate from a single cell, genetic mutations contribute to the emergence of a cancer cell. A series of mutations accumulate in successive generations, eventually there are enough mutations for the cell to become cancerous
What are a series of mutations accumulating in successive generations known as?
Clonal evolution
What is an oncogene?
over-active form of a gene positively regulates cell division
Give an example of an oncogene
Ras, Raf
What is a proto-oncogene?
Normal not yet mutated form of an oncogene
What is a tumour suppressor?
Inactive/non-functional form of a gene that negatively regulated cell division
Give an example of a tumour suppressor
Rb, p53
Describe the impact of p53 on sun exposure
Tp53 prevents cancer by ‘fixing problems’ but damage by sun exposure results in p53 mutations leading to lack of cancer control
Describe the mechanism by which p53 mutations arise
Cancer cell UVB specific damage Residual lesion Evasion of apoptosis by mutant p53 UV driven clonal expansion leads to further mutations & thus proliferation Tumour formation
Describe how different doses/patterns of exposure often lead to different cancers
Chronic/long term = SCC
Recreational/burning = Melanoma/BCC
Artificial UV = SCC/BCC/Melanoma
What type of skin cancer does chemical exposure increase your risk for?
Non-melanoma
Describe the damage caused by UVB and what it looks like
Direct DNA damage to the epidermis leading to sunburn
Describe the damage caused by UVA and what it looks like
Indirect oxidative damage of DNA bases in collagen leading to ageing
What happens when UBV is absorbed by DNA? How does this occur?
Absorbed to the double helix it causes
- CPDs
- 6-4 photo-products
Both occur by the formation of coolant bonds between adjacent pyrimidines on the same DNA strand
How does DNA repair itself after UVB forming CPDs and 6-4PPs?
- Recognition of damaged DNA
- Cleavage of damaged DNA on either side of photoproduct
- DNA polymerase fills in the gap
- DNA ligase seals the end
What happens when UVA causes oxidative damage?
8 oxo dG mispairs form leading to a GC to AT point mutation
How does DNA repair itself when bases are oxidised?
- Recognition and cleavage by DNA glycosylase
- Cleavage of deoxyribose by endonuclease
- DNA polymerase fills gap
- DNA ligase seals the ends
How does UV cause immunosuppression?
- depletion of langerhans
- generation of UV induced T cells with immune suppressive activity
- secretion of anti-inflammatory cytokines
What mutations are associated with BCC development?
PTCH1 mutations active hedgehog signalling to cause cell proliferation & angiogenesis
Name the drug that targets the hedgehog signalling pathway and can be used to treat BCC
Vismodegib
Mutations in what genes predispose to melanoma?
CDKN2A - prevents cells with damaged DNA replicating
CDK4 - permits cell cycle acting mutations to accelerate cell cycle
Where are melanocytes derived from?
Neural crest
What is the purpose of the MC1R protein?
Sits on cell surface and determines the balance of pigment in the skin and hair
Name the two main types of melanin
Eumelanin
Phaeomelanin
What is eumelanin responsible for?
Hair colour other than red
What is phaeomelanin responsible for?
Red hair
Name the portion that turns phaeomelanin to eumelanin
MCR1
What will on defective copy in MCR1 result in?
Freckles
What will two defective copies of MCR1 result in?`
Freckles and red hair
State another name for freckles
Ephilides
What are freckles?
Patchy increase in melanin - melanosomes produce increased melanin in response to sun exposure.
What are letingines?
Small pigmented macules as a result of increased melanocytes in the basal layer but does not darker after sun exposure - often found on sun exposed skin
Describe the histological finding of lentigines
Elongated rete pegs
What are the three common types of acquired melanocytic nave?
- Junctional
- Compound
- Intradermal
What type of melanocytes give a navei their colour?
Junctional melanocytes
What type of melanocyte cause a naevi to be raised?
Dermal melanocytes
Describe a junctional naevus
Melanocytes are at DEJ only so appear dark but flat, appear in childhood
Describe a compound naevus
Melanocytes at DEJ and in dermis so appears dark and raised, appear in adolescence