Testing for anal cancer typically starts with a simple physical exam and may progress to more specialized procedures depending on what your doctor finds. Most anal cancers are either visible on the skin around the anus or can be felt during a rectal exam, making early detection straightforward when you know what to look for and who to ask.
When Symptoms Warrant Testing
Anal cancer and common conditions like hemorrhoids share several symptoms, including pain, itching, and bleeding. That overlap is exactly why testing matters. A few patterns can help you distinguish between the two. Hemorrhoids tend to cause symptoms that come and go and improve with over-the-counter treatments. Anal cancer symptoms persist and gradually worsen. Pain, in particular, tends to get more intense over time with cancer rather than flaring up and settling down.
Bleeding is another key difference. Hemorrhoid bleeding is typically bright red, while anal cancer bleeding can be either bright or dark red. Other signs that should prompt testing include changes in bowel habits that don’t resolve, a persistent feeling of a lump near the anus, and unexplained discharge or itching. In its earliest stages, anal cancer may not produce any noticeable symptoms at all, which is why screening matters for people at higher risk.
The Digital Rectal Exam
The first and simplest test is a digital rectal exam. Your doctor visually inspects the skin within about 5 centimeters of the anal opening, then inserts a gloved, lubricated finger to feel the full circumference of the anal canal and lower rectum. The entire process takes a few minutes. Masses as small as 3 millimeters can be detected this way.
This exam catches a high percentage of cancers. In one study tracking the progression of precancerous lesions, 85% of anal cancers that developed were detected by palpation alone. About half of anal cancers are visible on the skin around the anus without any instruments at all. While a digital rectal exam isn’t a perfect screening tool on its own, it’s a reliable first step and requires no preparation or equipment.
Anal Pap Smear
An anal Pap smear works much like a cervical Pap smear. A small swab or brush collects cells from the lining of the anal canal, and those cells are examined under a microscope for precancerous or cancerous changes. The test itself is quick and causes minimal discomfort.
Anal Pap smears are better at catching abnormalities than ruling them out. Sensitivity ranges from 69% to 93%, meaning the test picks up most abnormal cells. But specificity is lower, between 32% and 59%, so a positive result doesn’t necessarily mean cancer is present. It means further testing is needed. Think of the anal Pap as a sorting tool: it identifies who needs a closer look, not a final diagnosis.
High-Resolution Anoscopy
If a Pap smear comes back abnormal, or if your doctor has other reasons for concern, the next step is usually high-resolution anoscopy (HRA). This is the gold standard for directly examining the anal canal and identifying areas that need a biopsy.
During the procedure, a short, lubricated tube called an anoscope is inserted about two inches into the anal canal. Gauze soaked in a mild acetic acid solution (essentially diluted vinegar) is placed against the canal lining for about two minutes. The acid causes abnormal tissue to turn white, making it visible. Your doctor then uses a high-powered magnifying scope, similar to what gynecologists use for cervical exams, to examine the tissue at 10 to 40 times magnification.
You’ll typically be asked to use an enema the morning of the procedure to clear the lower bowel. The whole thing is done in a clinic, and you go home the same day. If biopsies are taken during the anoscopy, you may have mild discomfort and light bleeding for a few days afterward.
Biopsy and Tissue Analysis
A biopsy is the only way to confirm whether anal cancer is present. During high-resolution anoscopy, any suspicious-looking areas are sampled with small tissue clips. These samples go to a pathology lab, where they’re examined under a microscope for specific signs of abnormal cell growth: cells that are larger than normal, irregularly shaped, with oversized nuclei and dense genetic material.
Pathologists classify what they find on a spectrum. Low-grade changes are mild and often resolve on their own. High-grade changes (called HSIL) are precancerous and carry a real risk of progressing to invasive cancer if untreated. When the distinction between low-grade and high-grade isn’t clear cut, labs can test for a specific protein marker called p16, which is overproduced in high-grade lesions and helps confirm the diagnosis.
Imaging for Staging
Once a biopsy confirms anal cancer, imaging tests determine how far it has spread. Two types of scans play complementary roles.
Pelvic MRI is the standard for evaluating the tumor itself. Its detailed soft-tissue images show how deeply the cancer has grown, whether it involves the sphincter muscles, and how close it extends toward surrounding structures. MRI is excellent for this local picture but limited in detecting cancer that has spread to lymph nodes or distant organs, especially when affected nodes are small or outside the pelvis.
PET/CT scanning fills that gap. It detects areas of unusually high metabolic activity anywhere in the body, flagging lymph nodes or distant sites that look normal on MRI but harbor cancer cells. In a meta-analysis of multiple studies, PET/CT changed the cancer stage in about 22.5% of patients and altered the treatment plan in roughly 1 in 5 cases. Most of those changes involved discovering lymph node involvement that MRI missed, leading to adjustments in radiation treatment fields. In approximately 3% of patients, PET/CT revealed previously unknown distant spread that fundamentally changed the treatment approach.
Who Should Be Screened Before Symptoms Appear
Certain groups face a significantly higher risk of anal cancer and benefit from routine screening even without symptoms. The International Anal Neoplasia Society recommends the following starting ages for screening:
- Age 35: Men who have sex with men and transgender women who are living with HIV
- Age 45: Other people living with HIV, and men who have sex with men and transgender women who are not living with HIV
- Age 45 with shared decision-making: People with a history of cervical or vaginal high-grade precancer or cancer, perianal warts, persistent cervical HPV16 infection lasting more than a year, or autoimmune conditions
Screening in these populations isn’t just about early detection. A landmark trial published in the New England Journal of Medicine found that treating precancerous anal lesions (HSIL) in people with HIV reduced the rate of progression to invasive cancer by 57% compared to monitoring alone. At four years, 0.9% of those who received treatment developed cancer versus 1.8% in the monitoring group. That’s a meaningful reduction in a cancer that becomes much harder to treat at advanced stages.
What the Testing Sequence Looks Like
For most people, testing follows a predictable path. It starts with a conversation about symptoms and risk factors, followed by a visual inspection and digital rectal exam. If anything feels or looks abnormal, or if you’re in a high-risk group undergoing routine screening, an anal Pap smear or high-resolution anoscopy comes next. Abnormal findings on either of those lead to a biopsy. A confirmed cancer diagnosis triggers MRI and PET/CT for staging.
The entire process from first exam to confirmed diagnosis can take a few weeks, depending on how quickly biopsies are processed and imaging is scheduled. None of the procedures require general anesthesia or an overnight hospital stay. The most invasive step, the biopsy during anoscopy, involves a few days of mild soreness at most.