What Is anal cancer?

Anal cancer occurs when cells in the anus begin to grow uncontrollably and form a malignant tumor, which can grow and spread (or metastasize) to other parts of the body. The anus is a fleshy tube that allows the passage of feces from the body. The anus connects to the rectum, which is the last portion of the gastrointestinal (GI) system. Food and liquid that a person consumes pass through the GI system, which absorbs nutrients and water that are needed to maintain healthy cells. The remaining waste from food forms feces, which are eliminated. Feces are held in the rectum by two muscles called sphincters before they can be passed. During defecation, the sphincters relax and feces pass through the anal canal and out of the body.

There are several forms of anal cancer, but the most common by far originates in squamous (pronounced SKWAY-muss) cells. These flat cells line the surface of the anus. As they turn cancerous, squamous cells penetrate deeper into the lining. This form of anal cancer, known as squamous cell carcinoma, commonly occurs in and around the opening of the anus. A less-common form of anal cancer, called an adenocarcinoma, occurs higher up in the anus, where it meets the rectum. Other uncommon forms include basal cell carcinoma, melanoma, and gastrointestinal stromal tumor.

What causes anal cancer?

Doctors have identified several risk factors that increase a person’s likelihood of developing anal cancer. Remember, having one or more of these risk factors makes you more likely to develop anal cancer, but does not guarantee that you will. If you have any of these risk factors, talk to your doctor about screening for anal cancer. According to the American Society of Colon & Rectal Surgeons, the risk factors for anal cancer include:

Infection with the human papilloma virus (HPV), a sexually transmitted disease (STD). HPV may or may not cause warts in and around the anus or genitals.
Being 55 or older
Engaging in anal sex
Acquiring an STD
Having multiple sex partners
Smoking
A history of HPV-related cancers, especially cervical cancer
Having a weakened immune system, such as from HIV, chemotherapy, or having an organ transplant
Having chronic inflamed areas about the anus, such as anal fistulas or open wounds
Having undergone prior pelvic radiation therapy for rectal, prostate, bladder, or cervical cancer

How common is anal cancer?

Anal cancer is relatively uncommon. In 2022, anal cancer represented about 0.5% of all cancer diagnoses in the United States, which added up to about 9,440 cases (and 1,670 deaths). By comparison, colorectal cancer represented nearly 8% of all cancer diagnoses in the United States, accounting for about 151,030 cases (and 52,580 deaths). Around the world, 50,685 people were diagnosed with anal cancer in 2020.

What are the signs and symptoms of anal cancer?

Anal cancer can cause the symptoms listed below. These symptoms can occur due to other medical problems, so if you develop any of the following, don’t assume you have anal cancer. However, if one or more of these symptoms arise and persist, see a doctor.

Bleeding or any unusual discharge from the anus
Pain or pressure in the anus
Itching in or about the anus
Swelling or lumps that form near the anus
Changes in bowel habits or in the diameter of your usual stool

How is anal cancer diagnosed?

Anal cancer is sometimes detected when doctors perform routine exams for other conditions, such as examining a patient for the presence of prostate cancer, or while conducting a pelvic exam or colonoscopy. Also, If a patient reports the symptoms listed above, a doctor may perform any of the following tests to determine if anal cancer may be the cause:

Digital rectal exam (DRE): A doctor inserts a gloved and lubricated finger into the anus to feel for lumps or other unusual formations.
Anal Pap test: A doctor uses a swab to remove cells from inside the anus, which are sent to a lab to be studied. Also called an anal Pap smear or anal cytology test.
Anoscopy: Using a small tube-shaped instrument called an anoscope, a doctor views the lining of the anal canal to look for unusual growths.

Anal cancer is not common enough to warrant routine screening (or testing for the disease in people who do not have symptoms). However, according to the American Cancer Society, doctors may consider screening people for anal cancer if they are at increased risk for a pre-cancerous condition called anal intraepithelial neoplasia (AIN). That includes:

People who are HIV positive
Men who have sex with men (regardless of HIV status)
Women who have had cervical cancer, vaginal cancer, or vulvar cancer
People who are immunocompromised, such as anyone who has received an organ transplant or requires long-term use of steroids

Additionally, doctors may consider screening patients who have a history of anal warts and women older than 45 years old who have tested positive for the strain of human papilloma virus called HPV 16.

How is anal cancer treated?

Many patients with anal cancer are treated with a combination of chemotherapy and radiation.

Chemotherapy: This common cancer treatment uses drugs that directly attack and kill cancer cells.

Radiation therapy: Also called radiotherapy, this treatment uses beams of high energy to kill cancer cells.

When anal cancer is detected early, it responds well to the combination of chemotherapy and radiation. If anal cancer is found very early, a doctor may be able to surgically remove the tumor, in which case no other treatment will be required. However, major surgery may be necessary if standard treatments for anal cancer are unsuccessful. In this procedure, known as an abdominoperineal resection (APR), a surgeon removes the anus, rectum, and the lower portion of the colon (called the sigmoid colon). Following an APR, a patient must undergo treatment to be able to pass stool from the body. A surgeon achieves this by connecting the colon to a hole in the abdomen called a stoma, which has a pouch (called a colostomy bag) attached to it that collects stool.

Some patients with anal cancer may be candidates for immunotherapy, which is the use of drugs that stimulate the body’s natural defense network, to recognize and kill cancer cells.

Sources: American Cancer Society, American Society of Colon & Rectal Surgeons

Anal Cancer