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How Is Anal Cancer Diagnosed?
What Tests Are Used to Diagnose Anal Cancer?
If you or your doctor notice signs that could point to anal cancer, such as bleeding, pain, itching, or a lump near the anus, the next step is testing. According to the American Cancer Society, about 11,270 people in the United States will be diagnosed with anal cancer this year. No single test can confirm this disease on its own. Instead, doctors use a set of exams, imaging scans, and lab tests together to find out whether cancer is present and, if so, how far it has spread. Below is a simple explanation of each test your care team may use.
Medical History and Physical Exam
Before any special test, your doctor will ask about your health history and your symptoms. This includes questions about bleeding, pain, changes in bowel habits, or a history of the human papillomavirus (HPV). The doctor will also check for swollen lymph nodes in the groin area, since anal cancer can sometimes spread there first. This simple step helps the care team decide which tests to order next.
Digital Rectal Exam (DRE)
A digital rectal exam, often called a DRE, is usually one of the first tests done. During this exam, the doctor puts on a glove, applies a lubricant, and gently inserts one finger into the anus and lower rectum. The doctor is feeling for lumps, thickened areas, or anything unusual. A DRE only takes a minute or two and may feel a little uncomfortable, but it should not be painful. The ACS explains that this exam allows a doctor to feel most anal cancers, since many tumors grow close to the anal opening. Because it is quick, low cost, and does not require any special equipment, many U.S. clinics use the DRE as a routine part of a checkup, especially for people at higher risk, such as those living with HIV.
Anoscopy
If the DRE finds something unusual, or if symptoms suggest a problem inside the anal canal, the doctor may perform an anoscopy. During this test, the doctor inserts a short, hollow, lighted tube called an anoscope a few inches into the anus. This lets the doctor look directly at the lining of the anal canal on a screen or through the scope itself. An anoscopy is done in the office, usually takes just a few minutes, and does not require sedation. Some people feel mild pressure, but it is generally not painful. This test lets the doctor spot abnormal areas, such as sores, growths, or thickened tissue, that might need a biopsy.
High Resolution Anoscopy (HRA)
High resolution anoscopy, or HRA, is a more detailed version of a standard anoscopy. Instead of using only the anoscope, the doctor also uses a colposcope, which is a lighted magnifying device that sits outside the body and allows a much closer, zoomed-in view of the anal lining. Before the exam, the doctor may apply a mild vinegar-like solution called acetic acid to the tissue, which temporarily turns abnormal cells a whitish color so they stand out. HRA usually takes about 15 to 30 minutes, does not require anesthesia beyond a numbing gel, and lets the doctor take pictures and collect tissue samples from any suspicious spots. HRA is especially useful for people at high risk of anal cancer, including people with HIV, organ transplant recipients, and people with a history of abnormal cervical or vulvar cell changes caused by HPV.
Anal Pap Test (Anal Cytology)
An anal Pap test, also called anal cytology, works much like the Pap test many women get during a gynecology visit. The doctor gently inserts a small swab into the anal canal and rotates it to collect a sample of cells from the lining. Those cells are sent to a lab, where a specialist looks at them under a microscope for changes that could be precancerous or cancerous. This test does not require any special preparation and usually causes only mild, brief discomfort. An anal Pap test is mainly used as a screening tool for people at higher risk of anal cancer, such as people living with HIV or men who have sex with men, rather than as a stand-alone way to diagnose cancer. If the results show abnormal cells, the next step is usually a high-resolution anoscopy with biopsy to look more closely.
Biopsy
A biopsy is the only test that can truly confirm anal cancer. During a biopsy, the doctor removes a small piece of tissue from an area that looks abnormal, often during an anoscopy or high-resolution anoscopy. The sample is sent to a lab, where a pathologist, a doctor who studies tissue under a microscope, checks the cells for cancer. The pathologist can also identify what type of anal cancer it is, most commonly squamous cell carcinoma, and may test the tissue for HPV. A biopsy can cause brief discomfort or light bleeding afterward, but serious problems are rare. According to the National Cancer Institute, a biopsy is the only way doctors can be fully sure that cancer is present, since imaging tests and physical exams can only suggest that something looks suspicious.
HPV Testing
Because most anal cancers are linked to human papillomavirus, doctors often test biopsy tissue for HPV DNA. The CDC estimates that about 91 percent of anal cancers in the United States, or roughly 7,600 cases a year, are caused by HPV infection. Knowing that a tumor is HPV positive can help guide treatment decisions and gives doctors useful information about how the cancer is likely to behave. HPV testing does not require a separate procedure beyond the biopsy sample already collected, so it adds little extra burden for the patient.
Endoanal or Endorectal Ultrasound
Once a cancer diagnosis is confirmed, doctors often need to learn how deep the tumor goes and whether it has reached nearby structures. An endoanal or endorectal ultrasound uses a thin probe that is gently inserted into the anus or rectum. The probe sends out sound waves that bounce off tissues and create a picture of the anal wall and surrounding area. This test helps doctors see how far the tumor has grown into the muscle layers of the anus, which is important for planning treatment such as radiation or surgery. The procedure typically takes about 15 to 30 minutes and may cause mild pressure but is not usually painful. It does not use radiation, which makes it a helpful option for checking tumor depth without extra radiation exposure.
MRI of the Pelvis
Magnetic resonance imaging, or MRI, uses strong magnets and radio waves, not radiation, to create detailed pictures of soft tissue inside the body. For anal cancer, a pelvic MRI helps doctors see the size of the tumor, how deep it goes, and whether nearby lymph nodes or organs look affected. During the scan, the patient lies still on a table that slides into a large tube-shaped machine. The test is painless, though some people feel a bit closed in, and it can take 30 to 60 minutes. Many U.S. cancer centers use pelvic MRI as a key tool for staging anal cancer before treatment begins.
CT Scan
A computed tomography scan, known as a CT scan, uses a series of X-ray images taken from different angles to build detailed cross-section pictures of the body. For anal cancer, a CT scan of the chest, abdomen, and pelvis helps doctors check whether cancer has spread to the lungs, liver, or other distant organs. Patients usually lie on a table that moves through a donut-shaped scanner, and the test often involves drinking or receiving a contrast dye that makes organs show up more clearly. A CT scan typically takes about 10 to 30 minutes and is painless, though some people feel a warm sensation when the contrast dye is given through a vein.
PET Scan
A positron emission tomography scan, or PET scan, helps doctors see how active cancer cells are throughout the body. Before the scan, a small amount of a radioactive sugar solution is injected into a vein. Because cancer cells tend to use more sugar than normal cells, they show up brighter on the scan images. A PET scan is often combined with a CT scan, called a PET/CT scan, to give doctors both function and structure information in one test. This combined scan is especially useful for checking whether anal cancer has spread to lymph nodes or other parts of the body, which affects the stage of the cancer and the treatment plan.
Blood Tests
Blood tests are not used to diagnose anal cancer directly, but they give doctors helpful information about overall health. A complete blood count checks red cells, white cells, and platelets, while liver function tests check how well the liver is working, since anal cancer can sometimes spread there. Because anal cancer is strongly linked to HPV, and people with HIV have a higher risk of developing it, doctors may also recommend an HIV test as part of the workup.
Putting the Tests Together
No single test tells the whole story. Doctors typically start with a physical exam and DRE, move to anoscopy or high-resolution anoscopy if something looks abnormal, and confirm the diagnosis with a biopsy. Once anal cancer is confirmed, imaging tests such as endorectal ultrasound, pelvic MRI, CT, and PET scans help determine the stage, meaning how far the cancer has grown or spread. Staging is important because it guides the treatment team, which often includes a colorectal surgeon, radiation oncologist, and medical oncologist working together at a U.S. cancer center, in choosing the safest and most effective treatment plan. If you have concerns about symptoms or your personal risk for anal cancer, talk with your doctor about which of these tests may be right for you.