How does high-risk HPV cause cancer?
HPV infects epithelial cells. These cells, which are organized in layers, cover the inside and outside surfaces of the body, including the skin, the throat, the genital tract, and the anus.
Once HPV enters an epithelial cell, the virus begins to make the proteins it encodes. Two of the proteins made by high-risk HPVs (E6 and E7) interfere with cell functions that normally prevent excessive growth, helping the cell to grow in an uncontrolled manner and to avoid cell death.
Many times these infected cells are recognized by the immune system and eliminated. Sometimes, however, these infected cells are not destroyed, and a persistent infection results. As the persistently infected cells continue to grow, they may develop mutations in cellular genes that promote even more abnormal cell growth, leading to the formation of an area of precancerous cells and, ultimately, a cancerous tumor.
Other factors may increase the risk that an infection with a high-risk HPV type will persist and possibly develop into cancer.19 These include:
- Smoking or chewing tobacco (for increased risk of oropharyngeal cancer)
- Having a weakened immune system
- Having many children (for increased risk of cervical cancer)
- Long-term oral contraceptive use (for increased risk of cervical cancer)
- Poor oral hygiene (for increased risk of oropharyngeal cancer)
- Chronic inflammation
Researchers believe that it can take between 10 and 30 years from the time of an initial HPV infection until a tumor forms. However, even when severely abnormal cells are seen on the cervix (a condition called cervical intraepithelial neoplasia 3, or CIN3), these do not always lead to cancer. The percentage of CIN3 lesions that progress to invasive cervical cancer has been estimated to be 50% or less.20
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Source: National Cancer Institute.