Anal Cancer Screening: Anal Pap and HPV DNA, Who and How

When it comes to anal cancer, many people feel too embarrassed to ask. I'd like you to think of it the same way as cervical screening in women: a test that takes a few minutes, needs no anaesthesia, and helps find lesions before they become cancer. For certain higher-risk groups, it's a very worthwhile test.

What causes anal cancer?

Most anal cancers are caused by long-term infection with high-risk types of human papillomavirus (HPV), especially HPV-16, which is found in most anal cancers. The virus gradually makes the lining cells abnormal, progressing from low-grade lesions (LSIL) to high-grade lesions (HSIL), which are precancerous. This process usually takes years, so there is a chance to detect and treat it first.

Groups at clearly higher risk than the general population are:

• People living with HIV, especially men who have sex with men (MSM) and trans women
• MSM and trans women without HIV
• Women who have had vulvar cancer or vulvar precancer
• Organ transplant recipients and people with weakened immunity from medicines or disease

Who should be screened, and from what age (IANS 2024)

The International Anal Neoplasia Society (IANS) published consensus guidelines in 2024, after the ANCHOR trial confirmed the benefit of treating precancerous lesions. In summary:

If you're in a risk group but haven't reached the starting age, and you have unusual symptoms such as a lump, bleeding or persistent anal pain, don't wait: get checked now.

Which tests are available?

• Anal Pap (anal cytology). A swab suited to the anus, such as a synthetic-fibre swab, is inserted about 4–5 cm, gently rotated while slowly withdrawn, and immediately placed in a cell-preserving liquid (liquid-based cytology). This reduces contamination and is more accurate than the old slide-smear method.
• High-risk HPV DNA testing (hrHPV) from the same liquid. Standard kits test a group of 14 high-risk types: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66 and 68, often reporting 16 and 18 separately.
• Co-testing of both cells and HPV.
• Digital anal rectal examination (DARE) should be done at every screening to find palpable lumps, and is the main method where HRA is not yet available.

Preparing for the test

1. Avoid anal sex, douching, suppositories, creams or lubricant in the anus for at least 24 hours before the test.
2. If you have inflamed haemorrhoids or a bleeding sore, tell your doctor; the test may be postponed.
3. During the test, you lie on your side with knees bent. Deep breaths help you relax. Most people feel only a few seconds of pressure.
4. There may be slight spotting afterwards, and you can carry on with normal life.

To learn how to look after this area day to day, read anal health 101.

Reading results and what happens next

• Normal (NILM) and/or HPV negative: repeat on schedule, about every 12–24 months depending on the type of test and your risk.
• Abnormal cells (ASC-US or higher) or HPV-16 detected: referral for high-resolution anoscopy (HRA), a magnified examination, with biopsy of any suspicious areas, is recommended.
• High-grade lesions (HSIL): treatment to prevent cancer, such as electrocautery or topical medication, as decided by a specialist.

The ANCHOR trial (Palefsky et al., NEJM 2022) in people living with HIV who had HSIL found that treating the lesions reduced anal cancer by about 57% compared with monitoring alone. This is why screening matters.

In Thailand, HRA is still available only at a limited number of hospitals, and your doctor will help plan a referral that fits your risk.

Prevention at the source

• HPV vaccine. It works best if given before infection, but adults at risk may still benefit. Talk to a doctor; see the HPV vaccine for women and men.
• Condoms reduce infection to some extent.
• People living with HIV: taking antiretrovirals to an undetectable viral load helps restore immunity (see HIV treatment).
• Stop smoking, because smoking increases the risk of HPV-related cancers.
• Get tested for other STIs regularly (see the 14-pathogen PCR STI test).

When to see a doctor right away

Whatever your age, if you have any of these, get checked without waiting for your screening date:

• Repeated bleeding from the anus
• A lump you can feel, or a sore that hasn't healed for more than 2–3 weeks
• Persistent pain, itching or discharge
• A change in bowel habits that lasts unusually long

Dr. Kris Clinic in Surat Thani offers Anal Pap and anal HPV DNA testing, with examination and counselling in a private, judgement-free setting, and helps arrange HRA referral when results are abnormal. English-speaking consultations are available. For an overview of health care, read LGBTQ+ health.