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Anal Cancer


Although rare, anal cancer is becoming more prevalent in the United States and many other developing countries. The condition develops in the tissues of the anus, which is a short tube that connects the lower part of the large intestine, known as the rectum, to the outside of the body. The anus allows the controlled disposal of body waste during bowel movements.

Like cervical cancer, the principal cause of anal cancer is human papillomavirus (HPV), a common virus that causes changes in the skin. Anal HPV infection is most commonly acquired through anal intercourse, but it can also be acquired from other genital areas that are infected, particularly from the vulva in women, or from the penis in men. Fingers and toys can probably lead to anal HPV infection as well.

Research suggests that sexually active individuals, both men and women, may be at risk for HPV. The good news is that only a fraction of people with anal HPV infection will develop a lasting case of anal intraepithelial neoplasia (AIN) — a precursor to anal cancer — and even fewer will develop anal cancer.

Other risk factors for anal cancer include:

  • Men and women with a history of anal intercourse
  • Men and women with a history of perianal warts, which are found outside the anus
  • Women with a history of vulvar warts, which are found outside the female genitals
  • Men and women who are chronically immunocompromised, such as those taking immunosuppressive medications, and those who are HIV positive, or those have received organ transplants

Additional risk factors include being over 50 years of age, having many sexual partners and smoking, which increases a person's chance of developing HPV.

Our approach to anal cancer

At UCSF, we specialize in the early detection and treatment of anal cancer, a rare cancer that's becoming more common. In addition, we help patients avoid anal cancer by finding and managing precancerous conditions. We are also active in research to develop more effective therapies for those conditions.

Our team includes experts with decades of experience specifically focused on anal cancer and HPV (human papillomavirus), which causes most anal cancers. We pioneered the use of a tool called a colposcope for diagnosing HPV-related diseases, as well as high-resolution anoscopy, considered the best technique for anal cancer screening.

Awards & recognition

  • usnews-neurology

    Among the top hospitals in the nation

  • Best in Northern California and No. 7 in the nation for cancer care

  • NIH-2x

    Designated comprehensive cancer center

Signs & symptoms

Patients with invasive anal cancer experience a wide variety of symptoms, but at the earliest stage of cancer, patients often have no symptoms. The most common symptoms include:

  • Pain or tenderness in the area around the anus, which can be constant or occur only with bowel movements or receptive sex
  • Bleeding with bowel movements or following sex that is different from normal
  • Lump or hard area on the outside of the anal area that appears to be increasing in size
  • Itching or discharge from the anus
  • Pain or a sense of fullness and constant need to go to the bathroom, or both, which may occur as tumors grow and begin to invade the sphincter muscle

If you are at risk of anal cancer or are experiencing symptoms, it is important to contact your doctor and be examined promptly. If cancer is detected, an early diagnosis will help improve outcomes and smaller tumors can be treated more effectively with fewer side effects.


In making a diagnosis of anal cancer, your doctor will first start by recording your medical history. This includes information about your general health, immune status, medications you are taking, and if you are HIV+, your current viral load and CD4+ lymphocyte count.

Your doctor will also ask about any history of anal warts, dysplasia or anal problems. You will also be asked about having a heart valve abnormality that is severe enough to warrant taking antibiotics when you have your teeth cleaned to prevent heart valve infections. If this applies to you, you will be prescribed antibiotics before having any biopsies, which may be part of your cancer diagnosis.

Next, your doctor will ask you to describe any symptoms you are currently experiencing, such as anal itching, discomfort, irritation, pain or difficulty with bowel movements or any problems that occur with anal sex, if applicable.

Your doctor may also recommend the following tests to make a definite diagnosis of anal cancer:

  • Digital rectal exam (DRE). A DRE involves the doctor or nurse inserting a gloved, lubricated finger into the rectum to feel for abnormalities. Even in patients without symptoms, something abnormal is usually felt during a DRE. If a mass, a thickening, an area of hardness, a lump, an area of localized tenderness or an ulcer is found, then the patient will be referred to a doctor specializing in anorectal problems who will evaluate and biopsy the suspicious areas.
  • High resolution anoscopy (HRA). This test involves looking through a microscope into the anus to look for abnormalities, such as ulcerated areas, thickened areas and lesions containing abnormal vessels. These areas are then assessed and biopsied during an HRA exam.
  • Proctoscopy. Also known as a sigmoidoscopy, this is an exam of the rectum using a short, lighted tube called a proctoscope.
  • Endo-anal ultrasound.  This is a special kind of ultrasound that uses high-energy sound waves to produce pictures of the inside of the body.
  • Rectal biopsy. A rectal biopsy is required to make a definitive diagnosis of invasive anal cancer. Patients with symptoms of anal cancer or those who have any abnormalities felt during a digital rectal exam (DRE) or identified during a high resolution anoscopy (HRA) will have a biopsy. This test involves removing a small amount of tissue from the rectum for examination by a pathologist to make a conclusive diagnosis.


If you are diagnosed with anal cancer, your doctor needs to learn the stage or extent of your disease. Staging is a careful attempt to find out whether the cancer has spread and to what parts of the body. This information also helps your doctor develop the best and most effective treatment plan for your condition. More tests may be performed to help determine the stage.

The various stages of anal cancer include:

  • Stage IS. The cancer is in its early stages and is found only in the innermost lining of the anus.
  • Stage I. The tumor is two centimeters or smaller in size.
  • Stage II. The tumor is larger than two centimeters in size.
  • Stage IIIA. A tumor of any size that has spread to nearby organs, such as the vagina, urethra and bladder, or has spread to the lymph nodes by the rectum.
  • Stage IIIB. A tumor of any size that has spread to nearby organs such as the vagina, urethra and bladder, and has spread to the lymph nodes by the rectum.
  • A tumor of any size that may have spread to nearby organs, and also has spread to the lymph nodes on one side of the pelvis and/or groin.
  • A tumor of any size that may have spread to nearby organs, and also has spread to the lymph nodes near the rectum and in the groin, and/or to lymph nodes on both sides of the pelvis and/or groin.
  • Stage IV. Any cancer that has spread to other distant parts of the body, such as the liver, lungs or brain.
  • Recurrent. Recurrent cancer means that the cancer has come back after treatment. The disease may recur in the anus or in another part of the body.


Treatment for anal cancer depends on many factors, including the location, type and stage of your tumor, as well as your age, health and personal preferences. Your doctor will discuss treatment options in detail with you and design the most effective plan for your condition.

Invasive anal cancer is curable in many patients, particularly when it is diagnosed early and tumors are small. Anal cancers are most commonly treated with a combination of chemotherapy and radiation, which causes tumors to completely regress in 80 to 90 percent of cases.

Surgery may be required for some cancers that do not respond to chemotherapy and radiation, or for those that recur after treatment with chemotherapy and radiation.


Chemotherapy uses drugs to kill cancer cells. Chemotherapy may be taken by pill, or it may be put into the body by a needle in a vein or muscle. Chemotherapy is called a systemic treatment because the drugs enter the bloodstream, travel through the body, and can kill cancer cells throughout the body. Some chemotherapy drugs can also make cancer cells more sensitive to radiation therapy.

Radiation therapy

Radiation therapy uses X-rays or other high-energy rays to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body, or external radiation therapy, or from putting materials that produce radiation, or radioisotopes, through thin plastic tubes in the area where the cancer cells are found, called internal radiation therapy. Radiation can be used alone or in addition to other treatments.

Side effects

Patients who receive chemotherapy and radiation therapy experience cumulative side effects that tend to worsen as the therapy continues. Immediate effects may include:

  • Skin reactions with redness around the anus
  • Inflammation of the skin
  • Occasional open sores or ulceration
  • Inflammation and irritation of the gastrointestinal tract, which may cause diarrhea or sores in the mouth, or both
  • Pain and inflammation of the rectum with soreness
  • Sense of urgency or needing to defecate
  • Low blood counts with possible sepsis

Late side effects may include:

  • Skin reactions with formation of scar tissue
  • Anal ulcers that can be quite deep
  • Death of anal tissue or stenosis, or both
  • Narrowing of the anus requiring colostomy in 6 to 12 percent of patients
  • Sterility and sexual dysfunction
  • Small risk of treatment-related leukemia, usually thought to be related to the therapy, mitomycin


In some cases, a surgical procedure called local excision may be used for select small anal tumors. This procedure is only recommended for small tumors that have not spread to other areas. During this procedure, the tumor is removed from the anus along with some surrounding healthy tissue. The sphincter muscle is not removed so that patients still have control over their bowel movements after surgery.

For other cases in which the tumor does not respond to chemotherapy and radiation, or for cases in which the tumor comes back after an apparent initial response, an operation called abdominoperineal resection may be required. During this surgery, an incision is made in the abdomen through which the anus, rectum, part of the colon and any lymph nodes containing cancer are removed.

The doctor then brings the end of the colon to the surface of the abdomen to create an artificial opening, called a colostomy. The colostomy serves as a substitute anus allowing the passage of body waste directly from the colon into a disposable bag outside the body. Our specially trained nurses will help you learn how to manage your colostomy and incorporate it into your lifestyle.

UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.

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