Almost all -- more than 99% -- cervical cancers are related to HPV. Of these, about 70% are caused by HPV types 16 or 18. Low-grade changes in the cells of the cervix are caused by a number of HPV types, including 16, 18, 6, or 11. Low-grade changes most often go away without treatment, although if they grow into warts doctors may remove them. But low-grade changes may also be caused by some high-risk HPV types as well as low-risk ones, and doctors who find low-grade changes often do more testing.
Nearly all cervical cancers are related to HPV, but most genital HPV infections do not cause cervical cancer. In research studies, most people who test positive for genital HPV will later test negative, often within 6 to 12 months. Scientists are still not sure if this means that a person's immune system has completely destroyed all of the HPV or has only suppressed the infection to an extremely low level (too low to be detected by the tests). If even a few cells of the cervix still contain HPV, it's possible that the virus may become active again if your immune system becomes very weak.
Changes in the cells of the cervix may suddenly happen many years after being exposed to HPV. These changes may be low-grade or high-grade. This delay helps explain how a woman could have changes in the cells of the cervix after many years of normal Pap tests and no new sex partner.
If cells stay infected with HPV, the virus may cause the cells of the cervix to change and become pre-cancer cells. True pre-cancer cell changes are called high-grade SIL (squamous intraepithelial lesions), sometimes abbreviated as HSIL. Another term for HSIL is CIN 2 and CIN 3. CIN is an abbreviation for cervical intraepithelial neoplasia.
Pre-cancer cells are not cancer. Some pre-cancer changes may return to normal on their own. But most cases of CIN 3 that are not found and treated are likely to progress to cervical cancer over about 10 years. Still, very few HPV infections lead to cervical cancer. Pre-cancer cells can be found before they have a chance to grow into cancer by having regular Pap tests.
For more information on cervical cancer, please see our document called Cervical Cancer.
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