What causes almost all cervical cancers?

Long-lasting infection with HPV (human papillomavirus) causes almost all cervical cancers. HPV is a common virus.

The word "long-lasting" carries most of the weight in that sentence. HPV infection is very common. Cervical cancer is not. What separates the two is whether the infection sticks around.

Not every HPV is the same

HPV is not one virus. It is a family of more than 200 related viruses. Most cause nothing, or cause warts.

The National Cancer Institute names 12 high-risk types: HPV 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, and 59. Types 16 and 18 cause most HPV-related cancers.

Your immune system clears most HPV infections on its own, usually within a year or two. Those infections never do lasting harm. Trouble comes when a high-risk type stays put for years and keeps irritating the same cells.

The slow road from virus to cancer

Cervical cancer usually develops slowly over time. Before cancer appears, the cells of the cervix go through changes known as dysplasia, in which abnormal cells appear in the cervical tissue. Over time, if not destroyed or removed, these abnormal cells may become cancer cells.

NCI puts numbers on that timeline. It takes about 5 to 10 years for infected cervical cells to become precancerous. It takes about 20 years to become cancer.

That long runway is the reason cervical cancer is one of the most preventable cancers. There is a wide window in which the problem is not yet cancer and can simply be removed.

Two ways to break the chain

Vaccination stops the infection. Gardasil 9 protects against nine HPV types, including the seven that cause most HPV-related cancers: 16, 18, 31, 33, 45, 52, and 58. NCI estimates the vaccine can prevent up to 90% of cancers caused by HPV, along with genital warts. NCI says vaccination is recommended at ages 11 to 12 and can start at age 9, because it works best before any exposure.

Screening catches the changes. Because of the link between HPV and cervical cancer, screening is an important part of routine health care for people with a cervix. NCI describes three tests. An HPV test looks for high-risk types. A Pap test looks for cell changes. A cotest does both.

The intervals NCI gives are:

• Ages 21 to 29: a Pap test starting at 21, then every 3 years
• Ages 30 to 65: an HPV test every 5 years, a cotest every 5 years, or a Pap test every 3 years
• Over 65: talk with your provider, since screening can often stop after years of normal results

Some clinics now let you collect the sample yourself during the visit. NCI suggests asking your provider if that interests you.

What this means for you

A positive HPV test is not a cancer diagnosis, and it is not a verdict on anyone's behavior. HPV is common enough that most sexually active adults are exposed at some point. What it means is that you should not skip the follow-up your provider recommends.

If you have been vaccinated, you still need screening. The vaccine covers most high-risk types, not all of them.

Smoking and a weakened immune system, including from HIV, make it harder for the body to clear HPV, which is why they show up on lists of cervical cancer risk factors.