Anal Cancer

Dr. Charles Lopez and physician assistant Jeff Donovan, talking
Dr. Charles Lopez (left), with physician assistant Jeff Donovan, is on our team of expert doctors for patients with anal cancer. Dr. Lopez is a medical oncologist (a doctor who treats cancer with medications) and a researcher.

At the OHSU Knight Cancer Institute, you receive care for anal cancer from a team of specialists. We offer you:

  • The only team-based program for anal cancer in Oregon.
  • Highly trained experts dedicated to treating gastrointestinal cancers, including anal cancer.
  • Specialists who meet weekly in meetings called tumor boards to combine their expertise for each patient.
  • Careful follow-up monitoring.
  • If needed, expert care for an ostomy, an abdominal opening so you can expel stool after anal cancer surgery.
  • A deep commitment to research, including a center devoted to early detection.
  • A full range of support services for you and your family.
Medical illustration of lower gastrointestinal anatomy
Anal cancer starts in the anus, the last part of the digestive tract. OHSU has Oregon’s only team-based program to treat this cancer.

Understanding anal cancer

The anus is the last part of the bowel or large intestine, after the rectum. It is about 1.5 inches long. When we digest food, the solid waste, or stool, exits the body through the anus. Anal cancer happens when abnormal cells grow in the tissue lining the anus. Most anal cancers are caught early, when they’re most treatable.

Anal cancer is rare, accounting for about 1-2% of intestinal cancers. An estimated 9,440 people in the U.S. are expected to be  diagnosed with anal cancer in 2022. 

People who have anal cancer are 70% as likely to survive at least five years from the time of diagnosis, as those who don't. This is called the five-year relative survival rate. The risk of dying from other causes is excluded. 

If the cancer is detected early, the five-year relative survival rate improves to 83%. 

Survival rates are averages, though, and can’t predict the outcome for an individual. They also, by definition, reflect the treatments that were available five or more years ago.

Risk factors include:

  • Age: Anal cancer is more common in people ages 55 to 64.
  • Gender: It’s more common in women, though that can vary by race and ethnicity. For instance, Black men are more likely to get anal cancer than Black women, at least before age 60.
  • Health history: Having a condition such as human immunodeficiency virus (HIV) can weaken your body’s natural defenses, increasing risk. Women with certain reproductive cancers (cervical, vulvar or vaginal) may also be at higher risk.
  • Sexual history: Having multiple partners, anal sex or unprotected sex increases risk of HIV, human papillomavirus (HPV) and other infections linked to anal cancer.
  • Smoking: Smokers are at higher risk.

HPV causes more than 90% of anal cancers, according to the National Cancer Institute. This virus spreads through skin-to-skin contact, including sexual activity. The virus can cause warts to form in the lining of the anus or on the skin outside the anus. These warts increase the risk of anal cancer.

The warts start out about the size of pinheads, so you may not notice them at first. Many people have no symptoms of an HPV infection until it progresses to a more serious condition such as anal cancer.

For women, screening tests normally done at the same time as a cervical cancer screening test (Pap smear) detect HPV. There is no HPV screening test for men. A vaccine for children and young adults (ages 9 to 26 but usually recommended at age 11 or 12) protects against HPV.

Anal cancer symptoms

Bleeding from the anus or rectum is an early symptom but can also be from hemorrhoids (swollen veins near the anus) or another condition. It’s important to talk with your doctor if symptoms such as rectal bleeding persist.

Other symptoms include:

  • Discharge from the anus such as pus or mucus.
  • Changes in bowel movements, such as narrow stools.
  • Itching near the anus that doesn’t stop.
  • Pain or pressure near the anus.
  • Swelling or a mass in the anus or nearby tissue.

Types of anal cancer

The two most common forms of anal cancer are:

  • Squamous cell carcinoma, which affects the cells lining the surface of the anus. This type accounts for nearly 90% of anal cancers.
  • Adenocarcinoma, which starts beneath the surface of the anus. This type affects cells that make mucus to lubricate the anus.

Other conditions include:

  • Rare forms of anal cancer include basal cell carcinoma and melanoma.
  • Anal intraepithelial neoplasia (precancerous cells) can occur when epithelial (skin) cells in the anus develop unusual features or form growths. 

Diagnosing anal cancer

Our team will do a thorough physical exam and tests that may include:

  • Digital rectal exam: Your doctor will use a gloved, lubricated finger to carefully feel the anus for warts or other masses.
  • Anal Pap smear: We collect a cell sample by gently scraping the anus with a plastic tool. We look at the cells under a microscope to check for signs of cancer.
  • Anoscopy: We use a short, hollow tube with a light, called an anoscope, to look at the lining of the anus. We can use a tool at the tip to take a tissue sample, called a biopsy, to examine under a microscope.
  • Proctoscopy: This test, similar to anoscopy, uses a longer tool called a proctoscope to see the far end of the anus and the rectum.
  • CT scan: This test uses X-rays to create 3D images of the anus to check for signs of cancer. Air is pumped in to expand the tissues for better images.
  • MRI scan: Radio waves and a large magnet create images of structures inside the body. The Knight Cancer Institute is the only center in Oregon with a 3 Tesla MRI to show small areas in great detail. 
  • Ultrasound: Sound waves create still or moving images of soft tissue inside the body. OHSU has contrast-enhanced ultrasound, which is not available at most hospitals. We inject dye for greater clarity, to help show whether a tumor is cancerous without the radiation exposure of a CT scan.
  • Chest X-ray: We may recommend an X-ray to see if cancer has spread to the lungs, a possible destination for metastatic anal cancer.

Anal cancer staging

Staging determines a tumor’s size, location and any spread. This process helps your care team develop the most effective treatment recommendations. We determine anal cancer staging through:

  • A physical exam
  • Imaging tests, such as ultrasound or magnetic resonance imaging
  • Evaluation of tissue samples

Tumor Sizes

This diagram illustrates tumor sizes compared with everyday items - a pea, a peanut, a grape, a walnut, a lime, an egg, as well as a pencil tip, a crayon tip, and a pencil eraser.

Stage I: The tumor is 2 centimeters or less.

Stage II:

  • Stage IIA: The tumor is larger than 2 centimeters but not more than 5 centimeters.
  • Stage IIB: The tumor is larger than 5 centimeters.

Stage III:

  • Stage IIIA: The tumor is no larger than 5 centimeters, and cancer has spread to lymph nodes near the rectum. These bean-size structures act as filters for the immune system.
  • Stage IIIB: Cancer has spread to nearby organs, such as the bladder, prostate gland or vagina.
  • Stage IIIC: The tumor is larger than 5 centimeters, and cancer has spread to the lymph nodes near the rectum. Or the tumor is any size, and cancer has spread to nearby organs and lymph nodes.

Stage IV: Cancer has spread to distant parts of the body such as the liver or lungs.

Coordinated care

Our gastrointestinal cancer experts work together to recommend a treatment plan for your individual needs. We gather weekly for a meeting called a tumor board, pooling our expertise for every anal cancer patient. Our specialists include:

  • Gastroenterologists, who do first evaluations and may remove early-stage cancers.
  • Surgeons, who specialize in complex pelvic procedures, including anal cancer care.
  • Medical oncologists, who treat cancer using medications.
  • Radiation oncologists, who treat cancer using radiation therapy.
  • Radiologists, who do imaging tests to see a tumor’s size and location.
  • Pathologists, who study tissue samples (biopsies) under a microscope to make or confirm a diagnosis.

Anal cancer treatment

In most cases, a combination of chemotherapy and radiation therapy removes the cancer. If cancer cells remain or if anal cancer comes back, surgery can help.

Chemotherapy and radiation

Chemotherapy uses medications, usually given in a slow IV drip, to destroy cancer. We offer community cancer clinics throughout the Portland area.

Radiation therapy uses powerful beams of energy to destroy cancer. At the Knight Cancer Institute, you have access to the latest radiation therapy techniques, such as:

  • 3D conformal radiation therapy: We direct radiation beams to match the exact shape and location of your tumor. This allows us to use a higher dose without harming healthy cells.
  • Intensity-modulated radiation therapy: This is a type of 3D conformal radiation therapy. It enables us to vary the radiation to different parts of the tumor, lowering the risk of side effects.


Expertise: Our team includes several surgeons with fellowships in colorectal surgery, including anal cancer procedures. These fellowships mean our providers have at least an additional year of advanced training.

Minimally invasive surgery: We use minimally invasive techniques, with small incisions and sophisticated instruments, whenever possible. This results in less pain and faster recovery.

Ostomy care

If you have surgery to remove anal cancer, you will no longer be able to have bowel movements through your anus. You will have a procedure called a permanent colostomy. Your surgeon will create an opening (stoma) in your large intestine and belly. The stoma will connect to an ostomy bag outside your body to collect stool.

Our team includes nurses with special training to help you overcome fears, find ostomy products and learn to care for your ostomy. An ostomy won’t keep you from doing sports or other activities you enjoy.


Because anal cancer can come back, your care team will schedule regular follow-up visits. This enables us to detect the earliest signs of cancer, giving you the best chance for successful treatment.

Learn more

For patients

Call 503-494-7999 to:

  • Request an appointment
  • Seek a second opinion
  • Ask questions


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Center for Health & Healing Building 2
3485 S. Bond Ave.
Portland, OR 97239
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