Anal Cancer Screening for MSM — What to Know
Anal cancer rates in MSM (men who have sex with men) are 20-40 times higher than in the general population. HIV-positive MSM have rates as high as 90 per 100,000 — comparable to historical cervical cancer rates in the era before Pap smears.
Until 2022, there was real debate about whether screening worked. Then the ANCHOR trial published results that changed the conversation. Here's where things stand in 2026.
The short answer
- Who's at highest risk: HIV-positive MSM (highest), HIV-negative MSM (higher than general), women with cervical/vulvar HPV, immunosuppressed people
- Most cases are caused by HPV-16 (sometimes 18) — the same strain that drives cervical cancer
- Screening tools: Anal Pap (cytology), HPV DNA testing, digital anorectal exam (DARE), high-resolution anoscopy (HRA)
- 2024 ANCHOR trial: Proved screening + treatment of precancerous lesions reduces anal cancer incidence by ~57% in HIV+ adults
- Current guidelines: Routine anal cancer screening recommended for HIV+ MSM age 35+; consider for HIV-negative MSM 45+
Who should be screened
The most current expert recommendations (2024-2026):
Strong recommendation for screening
- HIV+ MSM age 35 and older (based on ANCHOR trial)
- HIV+ transgender women age 35 and older
- Solid organ transplant recipients
Reasonable to screen
- HIV-negative MSM age 45 and older
- HIV+ heterosexual men or women age 45 and older
- Women with high-grade cervical or vulvar HPV disease
- People with chronic immunosuppression
Routine screening NOT recommended
- HIV-negative heterosexual men or women without risk factors
- Anyone under 35 with HIV (some experts disagree — discuss with your provider if you have specific concerns)
How screening works
There are three main tools, often used together:
1. Digital anorectal exam (DARE)
- Gloved-finger exam of the anal canal
- Can catch palpable masses
- Should be part of any annual physical for high-risk people
- Doesn't catch precancerous lesions but does catch advanced cancers
- Some clinicians recommend annually for HIV+ MSM
2. Anal Pap (anal cytology)
- Like a cervical Pap but for the anal canal
- Provider inserts a small swab and rotates to collect cells
- Cells sent to pathology, graded as:
- Normal
- ASC-US (atypical cells of undetermined significance)
- LSIL (low-grade squamous intraepithelial lesion)
- HSIL (high-grade squamous intraepithelial lesion) — the precancer
- AIN1, AIN2, AIN3 — alternative histopathologic grading
- Sensitivity is moderate (50-80%); specificity is moderate
3. High-resolution anoscopy (HRA)
- A magnified visual exam of the anal canal using a colposcope
- Done by specially trained providers
- Suspicious areas are biopsied
- The "diagnostic gold standard"
- Requires a specialist visit and is uncomfortable but tolerable
- Often done if anal Pap is abnormal
Newer/Adjunct tools
- Anal HPV DNA testing — can be combined with anal Pap
- HPV-16 / HPV-18 typing — high-risk strain identification
The ANCHOR trial — why it changed practice
The Anal Cancer HSIL Outcomes Research (ANCHOR) trial was the largest randomized controlled trial of anal cancer screening, published in NEJM in 2022 with extended follow-up reported through 2024.
Design
- ~4,500 HIV-positive adults age 35+ enrolled
- All had HSIL (high-grade precancer) identified
- Randomized to either:
- Treatment of HSIL (electrocautery, infrared coagulation, topical agents)
- Active monitoring with HRA every 6 months
Result
- The trial was stopped early because of a clear benefit in the treatment arm
- 57% reduction in progression to anal cancer
- The treatments were tolerable; no major safety signal
Implication
ANCHOR is the equivalent of the Pap smear trials for anal cancer in high-risk populations. It transformed anal cancer screening from "maybe useful" to "proven to reduce cancer rates."
What screening looks like in practice
Typical workflow for an HIV+ MSM patient age 40
- Annual DARE as part of physical
- Anal Pap every 1-2 years (frequency depends on results and risk)
- If anal Pap is abnormal: referral for HRA
- If HRA shows HSIL: treatment (electrocautery, IRC, topical)
- Surveillance after treatment: HRA every 4-6 months for first year, then annually
Frequency varies by setting
- Some programs use anal Pap as primary screen
- Some use direct HRA every 1-2 years
- Some use HPV DNA + cytology combination
- Practice varies because guidelines are evolving
Where to get screened
- HIV clinics: Often integrated into routine care
- Sexual health clinics (Howard Brown, Callen-Lorde, similar major-city LGBTQ health centers)
- Colorectal surgery practices with HRA capability
- Some academic medical centers have anal cancer screening programs
Access challenges
- HRA is not widely available — many cities have only 1-2 providers
- Insurance coverage is improving but variable
- Some patients travel for specialty screening
The International Anal Neoplasia Society (IANS) maintains a directory of qualified providers.
What treatment looks like
If HSIL is identified, treatment options include:
Office-based ablation
- Electrocautery (EC) — most common; uses heat to destroy abnormal tissue
- Infrared coagulation (IRC) — uses infrared light
- Cryotherapy — uses freezing
Topical treatments
- Imiquimod 5% — immune-modulating cream applied to lesion
- Topical 5-fluorouracil — chemotherapy cream
- Topical trichloroacetic acid (TCA)
For larger or recurrent lesions
- Surgical excision under anesthesia
Recurrence is common (30-50%) — surveillance is required.
Anal cancer symptoms — when to bypass screening and see urgently
Don't wait for routine screening if you have:
- New bleeding from the rectum
- New rectal pain
- A palpable lump in the anus
- Persistent itching or discharge
- Change in bowel habits
- Unexplained weight loss
These warrant prompt evaluation, not just routine screening.
Prevention beyond screening
HPV vaccination
- Gardasil 9 covers HPV-16, the main anal cancer driver
- Recommended through age 26; can be given through 45
- Even after HPV exposure, vaccine likely provides some benefit against new strains
- See HPV vaccine for adults over 26
Smoking cessation
- Smoking significantly increases anal cancer risk in HPV-infected people
- Quitting reduces progression risk
HIV management
- Undetectable viral load improves immune function and may slow HPV-related disease
- See U=U Explained
Condom use
- Reduces but doesn't eliminate HPV transmission
- See do condoms prevent STIs?
What to ask your doctor
"Given my HIV status / age / sexual history, should I be screened for anal cancer?"
"What's the screening approach here — anal Pap, HRA, or both?"
"If I need HRA, where do I go?"
"How often should I be screened?"
"Am I a candidate for HPV vaccination?"
Common misconceptions
"Only HIV+ people get anal cancer." False — but rates are highest in HIV+ MSM. Anyone with persistent HPV infection at the anus is at risk.
"Anal Pap alone is enough." Not really — anal Pap has imperfect sensitivity. HRA is the diagnostic gold standard.
"Screening hasn't been proven to work." ANCHOR (2022) changed that. For HIV+ adults 35+, screening + treatment reduces cancer.
"I have to be having anal sex to be at risk." HPV can be acquired through receptive anal sex, but also through other genital contact and infection from previous sexual exposure.
Bottom line
If you are:
- HIV-positive MSM age 35+ → routine anal cancer screening is now strongly recommended
- HIV-negative MSM age 45+ → consider screening (discuss with provider)
- Anyone with high-grade cervical or vulvar HPV → consider anal screening too
- Immunosuppressed (transplant, chronic conditions) → consider screening
What "screening" means: annual DARE + anal Pap every 1-2 years, with HRA referral for abnormal results. HSIL treatment if identified.
Anal cancer is preventable. The infrastructure to screen at scale is still being built — but if you're in a high-risk group, ask your doctor about it. The data on benefit is now strong.
For more on HPV — vaccine, warts, cervical cancer risk — see our HPV pillar guide, HPV in men, and HPV vaccine for adults over 26.
