Why HIV raises the risk of certain cancers

HIV does not turn into a tumour. The link between HIV and cancer runs through the immune system instead.

NCI puts it this way. Infection with HIV weakens the immune system. That reduces the body's ability to fight viral infections. It also reduces the body's ability to fight virus-infected cells that can turn into cancer.

So the chain has three links. First, HIV damages immune defences. Second, other viruses become more active. A healthy immune system would keep those viruses quiet. Third, some of those viruses can push cells toward cancer.

NCI names four groups of viruses. They account for most of the raised cancer risk in people with HIV:

• Kaposi sarcoma-associated herpesvirus, also called human herpesvirus 8
• Epstein-Barr virus
• Human papillomaviruses
• Hepatitis B and hepatitis C viruses

This explains a pattern that would otherwise look random. The cancers that go up are the ones tied to these viruses. Cancer in general does not go up.

Three cancers were once called AIDS-defining. They are Kaposi sarcoma, aggressive non-Hodgkin lymphoma, and cervical cancer.

For the years 2015 to 2019, NCI compares people with HIV to the general population:

• Kaposi sarcoma: more than 200 times higher
• Anal cancer: nearly 20 times higher
• Burkitt lymphoma: about 15 times higher
• Cervical cancer: three to four times higher
• Lung cancer: 1.6 times higher

A figure like "200 times" is startling. It helps to know what it compares. Kaposi sarcoma is uncommon in the general population. So a large multiple can still mean a fairly small number of people. These figures show where attention should go. They are not a forecast for any one person.

Combination antiretroviral therapy arrived in the mid-1990s. In NCI's words, it greatly reduced the incidence of certain cancers. That was true above all for Kaposi sarcoma and non-Hodgkin lymphoma.

This is one of the clearest cancer prevention results in modern medicine. And it came as a side effect of treating the infection itself.

The honest caveat comes right after. People with HIV still face significantly elevated cancer risks. That is because cART does not fully restore how the immune system works.

Treating HIV well is the strongest single way to cut these cancer risks. It does not cut them to zero.

The raised risks sit in a few named cancers. So screening is targeted, not general. NCI describes the following:

• Cervical cancer screening with Pap tests. It starts at HIV diagnosis and continues through life. HPV co-testing is an option from age 30.
• Anal cancer screening. It begins at age 35 for men who have sex with men, and at age 45 for others.
• HPV vaccination. NCI notes that CDC recommends three doses for people aged 9 through 26 who are living with HIV or immunocompromised. For ages 27 to 45 the vaccine is approved but not routinely recommended, and is worth discussing with your doctor.

If you live with HIV, bring these up at your next visit. They are also a good reminder. This is a managed situation with a plan attached. It is not just something to worry about.

Many people with HIV see an HIV specialist often. They see a primary care clinician now and then. Cancer screening can slip between the two.

Cervical screening runs on a different schedule than it does for the general population. Anal screening starts at a set age. Both are easy to lose track of when no one owns them.

So ask plainly. Who makes sure my screening happens? And how will I be reminded?

Put vaccination on the same list. CDC recommends three doses of HPV vaccine for people aged 9 through 26 living with HIV. From 27 to 45, it is approved but not routinely recommended, so it is a conversation to have. If no one has asked you about it, ask them.

The wider picture is far more hopeful than it was a generation ago. Treatment that suppresses HIV has already cut rates of some of these cancers a great deal. The risk that remains is being managed, not just watched.