15: Skin Cancer Flashcards
Malignant melanoma
Malignant tumour of melanocytes
Most common in white-skinned people
Incidence increasing in western countries
In UK, higher prevalence in south-west because UV light is stronger and they spend more time outside
Caused by UV exposure + genetic factors
Types of UV light?
UVC - blocked by ozone layer
UVB - most important wavelength in skin cancer
UVA - also contributes to skin cancer
What effect does UVB have?
Directly induces abnormalities/mutations in DNA
Induces photoproducts
Causes cross-linking of pyrimidines (T and C)
Usually repaired quickly by nucleotide excision repair, if not leads to carcinogenesis
What is Xeroderma pigmentosum
Genetic condition
Defective excision nucleotide repair
Mutations that cause cancer?
- p53 -> uncontrolled cell proliferation
- Alter response to growth stimulating/suppressing factors
- Inhibit apoptosis
What happens in sun burn?
Prolonged exposure to UV
Build-up of mutations leads to keratinocyte apoptosis
How does photocarcinogenesis occur?
UV -> DNA damage -> p53 mutation -> skin cancer
Immunomodulatory effect of UV?
UVA/UVB depletes Langerhans cells in epidermis
Reduces immune function
So abnormal cells less likely to be removed by immune system
What is melanin?
Responsible for skin color
Made from tyrosine
Produced by melanocytes in basal layer of epidermis after exposure to sun
Present around keratinocytes
2 types:
Eumelanin = brown/black (african)
Phaeomelanin = yellow/red brown (redheads)
What gene regulates melanin?
MCR1 gene
Polymorphism determines which type it produces more
Squamous cell carcinoma
Malignant tumour of keratinocytes Caused by: - UV exposure - HPV - Immunosuppression -
Squamous cell carcinoma
Malignant tumour of keratinocytes Caused by: - UV exposure - HPV - Immunosuppression
Epidermodysplasia veruciformis
Rare autosomal recessive condition
Risk of HPV-induced warts and SCCs
