There are over 100 types of HPV. A small number of these infect squamous mucosa, whereas the majority infect the squamous epidermis. Certain high risk species are associated with 99% of squamous cell carcinoma of the cervix, as well as a number of other squamous cell carcinomas (anal, vaginal, vulval, and oropharyngeal and other head and neck mucosal sites).
HPV is a small virus that contains nine genes. Seven of these are early genes expressed at infection; E6 and E7 are involved in promoting cell survival and proliferation. L1 and L2 code the viral capsid protein.
- E6 binds to and inhibits TP53
- E7 binds to and inhibits RB1
Inactivation of these important proteins can lead to cell immortalisation and ability to acquire other genetic mutations without consequence. The timeline between infection and malignancy is thought to be at least 10 years. Interaction of HPV with other host and environmental factors (eg. HIV infection and immunodeficiency or smoking) is known to occur and may accelerate or promote the development of malignancy.
In head and neck cancer, HPV associated squamous cell carcinomas are frequently basaloid in architecture. They have increased sensitivity to treatment.