25: HPV Flashcards
first evidence of cancer
mediated by viruses
discovery in the early 1900s with chickens developing sarcoma in breast muscle
viruses and cancers in humans
approximately 12% caused by viral infection (more than 80% of cases in the developing world)
1 out of 3 suffer from cancer so 12% caused by viral infection is quite a lot
human viruses associated with cancer
hepatitis b (HBV)
hepatitis c (HCV)
epstein barr virus (EBV)
high-risk human papilloma viruses (HPVs)
human t-lymphotrophic virus-1 (HTLV-1)
kaposi’s sarcoma herpesvirus (KSHV)
why do viruses not want cancer?
typically an accident leading to a dead-end for the virus
are viruses necessary for cancer development?
necessary but not sufficient
- cancer incidence lower than virus prevalence
80% of the population infected with EBV
- vast majority never develop cancer associated with viruses
when are viral cancers likely to appear?
context of persistent infections
- the longer they stay, the more time they have to cause cancer
immunosuppressed have more chances to develop cancer associated with viruses since you can’t control the virus
the immune system can play a deleterious or protective role
inflammation can sometimes be pro-cancer
- inflammation as a major player giving rise to cancers (carcinoma associated with hepatitis)
other human virus-associated cancers increasing with immunosuppression
what is cancer?
uncontrolled growth of abnormal cells in the body
- develops when the body’s normal control mechanism stops working
old cells don’t die but grow out of control forming new/abnormal cells
once cancer is invasive, metastatic is harder to get rid of since cancer is in other parts of the body
types of genes linked to cancer
proto-oncogenes - proteins which normally contribute positively to cell proliferation
- tightly-regulated proteins which push cells to growth when on
- mutations can alter the regulation of proto-oncogenes which prevents them from being turned off
tumour suppressor genes - proteins that prevent the unwanted proliferation of mutant cells
- monitors cells for uncontrolled growth
- mutations render them ineffective
for cancer, you need proto-oncogenes turned on to become oncogenes and tumour suppressors to be turned off
modulation of host cell cycle
viruses subvert cell cycle to their advantage
cell makes nucleotide synthesis which the virus wants since it wants to replicate its own genome and needs energy
target specific steps of the cycle to improve viral replication
- viruses encode oncogenes and tumour suppressor inhibitors
- not because they want it to become a tumour but because they want the cells to be in a phase/stage favourable for viral synthesis
how many species of HPV?
over 100 recognises species which infect humans
HPV infection
asymptomatic (vast majority of HPVs)
cause genital/skin warts
- highly specific for some parts of the body
infection carries a risk of becoming cancerous
- 40 types of HPV affect the genitals and some carry cancers
HPV as the most commonly sexually transmitted infection in the US
> 80% of people infected with at least one type of HPV in their lives
- 40% of these 80% will have symptoms while others are asymptomatic
most infections clear on their own within two years
low-risk HPV
don’t typically cause symptoms
no association with cancer but lead to genital warts
HPV 6 and 11
believed that 1% of people in the US have warts at any given point
high-risk HPV
extensive cervical dysplasia and certain types of cancers
only HPV 16 and 18 which cause the majority of HPV-related cancers (70%)
- leads to pre-cancerous and cancerous lesions
