Cancer Flashcards
UVB causes - - - and is
- more damaging that UVA when sun directly overhead
direct DNA damage
1000x
UVA causes - - -
UVA does what compared to UVB?
indirect oxidative damage
Penetrates more deeply into skin
UVC is blocked by ozone layer t/f
t
What can block UVB?
Sunscreen and window glass
What can block UVA?
Sunscreen
Both UVB and UVA can cause sunburn t/f
UVB only
What is the UV signature DNA damage pattern?
Pyrimidine dimer, covalent bonding between adjacent pyrimidines on the same DNA strand
Only UVB can cause pigmentation, but both uva and uvb cause skin cancer and ageing
both types cause pigmentation, skin cancer and ageing
Cells can be morphologically normal but still have abnormal genetic mutations t/f
T
What is an oncogene?
Over-active form of a gene that positively regulates cell division
Drives tumour formation when activity or copy number is increased (accelerator) e.g. Ras, Raf, growth factor receptors
What is a tumor supressor gene?
Inactive or non-functional form of
a gene that negatively regulates cell division
Prevents the formation of a tumour when functioning normally (brake) e.g. Rb, TP53
Most skin cancers are melanomas t/f
f
mostly non melanomas
Melanoma most serious type of skin cancer t/f
t
skin cancer risk factors
UV radiation
Genetics
Age
Chemical exposure
Immune suppression
Chronic or long term sun exposure likely to cause which typer of cancer?
Squamous cell carcinoma
Intense intermittent
and
recreational likely to cause which typer of cancer?
Melanoma, Basal cell carcinoma
Artificial UV is likely to cause BCC t/f
f
all three tyes
What is Xeroderma pigmentosum?
rare autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet (UV) light is deficient.
What is the signature DNA mutation caused by UV exposure?
Pyrimidine Dimer: covalent bonding between adjacent pyrimidines on the same DNA strand
What are the effects of UV induced immunosupression?
Depletion of Langerhans cells in the skin and reduced ability to present antigens
induction of regulatory T cells
Secretion of anti-inflammatory cytokines
What are the three stages of acquired naevi development?
Childhood - JUNCTIONAL NAEVUS: clusters of melanocytes at EDJ
Adolescence - COMPOUND NAEVUS: clusters as EDJ and dermis
Adult - INTRADERMAL NAEVUS: all EDJ activity ceases, entirely dermal
What is the gene that determines balance of pigment in skin and hair?
Melanocortin 1 receptor
Defective melanocortin 1 receptor gene causes freckles and red hair t/f
ONE copy = FRECKLES
TWO copies = FRECKLES & RED HAIR
What are ephilides?
freckles
What are actinic lentignes?
‘liver spots’ related to UV exposure
Inc. Melanin and melanocytes
Congenital naevi are always bening t/f
F
large lesions have a 10-15% risk of melanoma, may need surgical excision
How are aqcuired naevi induced in infancy?
Breakdown in melanocytes : keratinocyte ratio
the process is thought to be immune regulated
It is easy to tell the difference between dysplastic naevi and melanomas t/f
F
Both have variable pigment and border assymetry
Features of dysplastic naevi?
> 6mm
precursor to malignant malinoma
variable pigment
border assymetry
Features of halo naevi?
- peripheral halo of depigmentation due to damage by inflammatory cells. Pigmented centre
Features of blue naevi?
- entirely dermal
- consist of pigment rich dendritic spindle cells
- The cellular variant may have mitoses and mimic melanoma