Bleeding and discomfort are the most common symptoms of anal cancer. But you might also develop loose and more frequent or thinner stools if a tumor restricts movement through the anus. Anal cancer treatments include chemotherapy, radiation therapy, and more.

Anal cancer is a type of cancer that develops in the lowermost portion of your bowels, where stool exits your body.

Unlike colorectal cancers, changes in the type, color, or texture of your stool don’t always happen — but they are possible.

Keep reading to learn what kind of bowel changes you might expect if you develop anal cancer.

What’s the difference between anal cancer and colorectal cancer?

Anal cancer develops in the lowermost part of your digestive tract, where stool exits your body. Colorectal cancer develops in the colon or rectum — which are both sections of your large intestine.

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Bleeding from the anus is usually the first symptom people who develop anal cancer notice. While this blood doesn’t exactly change the shape or texture of poop, it can change the color.

Bleeding from your upper gastrointestinal system appears dark maroon, but bleeding from anal cancer is a brighter red and can either be in your stools or leak from the anus on its own.

For some people, cancer may also change the frequency and texture of your poop. You may have to go more frequently or you may have looser stools (diarrhea).

Finally, anal cancer can restrict the movement of stools through the anus, giving your poop a narrower or smaller shape than you’re used to.

Bleeding and discomfort are the primary symptoms of anal cancer, but there’s a range of other possible symptoms you may develop.

Some of the most common symptoms of anal cancer are:

Infection with the human papillomavirus (HPV) is the leading cause of anal cancer. There are more than 150 types of HPVs. The HPV causes conditions like genital warts and other cancers.

The HPV is transmissible through skin-to-skin contact. In the case of anal cancer, sexual contact is the primary way of sharing the virus. As such, sex without a condom or another barrier method is a major risk factor, but there are others, too.

Anal cancer may develop more often in people who smoke or have:

Additionally, when reviewing how often anal cancer occurs among people of certain genders or racial groups, white people assigned female at birth and Black people assigned male at birth tend to be affected more often.

Anal cancer may be preventable through many lifestyle changes, such as:

If you have a high risk of developing anal cancer, talk with your doctor about screening for it.

Doctors can perform regular screening with a digital rectal examination or anal cytology testing. Cytology testing uses a swab to collect cells from your anus for microscopic analysis, similar to Pap smear testing.

Doctors usually diagnose anal cancer during a routine colonoscopy or while your doctor examines you due to a specific concern, like bleeding.

In addition to a colonoscopy, your doctor will need to perform a physical examination to make a diagnosis. This can include a digital rectal exam, blood testing, or even direct visualization using an anoscopy, a small viewing tool a doctor inserts into the anus. A doctor may also need to perform imaging studies, like an X-ray or a CT scan.

In addition to identifying anal cancer, your doctor will use this diagnostic testing to stage your cancer and determine whether the spread involves other areas of the body.

Anal cancer can be treatable surgically by removing a tumor, or portions of the anal canal. A doctor may need to remove other areas of the bowel, too, if the cancer spreads beyond the anus.

Other, less invasive treatment options include:

Your doctor may combine some of these treatments or add additional medications to make treatment more effective. These are called adjuvants. One example is radiosensitizers, which increase the sensitivity of cancer cells to radiation treatment.

Anal cancer is a type of cancer that affects the lowermost part of your bowels. The HPV often causes it, and it is transmissible through sexual contact.

Bleeding and discomfort are common concerns among people with anal cancer, but you could also develop changes to your poop.

The most common stool changes include discoloration from bleeding, loose stools or diarrhea, or narrowed stools if a tumor restricts the movement of poop through your anus.