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What Is Anal Cancer?

Knowing the symptoms of this rare form of cancer could help ensure an early diagnosis.

Laura Simmons - Editor and Staff Writer

Laura Simmons

Laura Simmons - Editor and Staff Writer

Laura Simmons

Editor and Staff Writer

Laura is an editor and staff writer at IFLScience. She obtained her Master's in Experimental Neuroscience from Imperial College London.

Editor and Staff Writer

hand holding toilet roll in front of toilet

Changes in bowel habits can be a sign of anal cancer.

Image credit: Me dia/

Anal cancer is a rare and often overlooked form of the disease. Like with other cancers affecting the digestive system such as colon or bowel cancer, some of the symptoms can be tricky to talk about – not everyone feels comfortable with discussions around going to the toilet, even with their doctor. But it’s important to be aware of the signs because starting treatment at an early stage can make all the difference. So, let’s shed some light on what can be a difficult topic, and explore what we know about anal cancer.

What is anal cancer?

First, a quick anatomy refresher. Anal cancer is a type of cancer that starts in the anus, the opening where your intestines meet the outside world. To be totally clear: it’s where your poop comes out.


Waste products left behind when digested food has passed through the small and large intestines are stored in the rectum as feces. When you have a bowel movement, this feces is passed out of the body through the anus. 

The rest of the time, the anal opening is kept closed thanks to muscular rings called sphincters. The area of tissue immediately before the opening is called the anal verge, and the inner lining of the anal canal is called the mucosa. It’s here, in the mucosa, where most anal cancers start.

According to the American Cancer Society, anal cancers are often divided into two groups: those that start above the anal verge, within the anus itself; and those that start in the skin just below the anal verge, called the perianal region. It can be tricky to tell exactly where someone’s cancer started though, because cancerous cells can extend from one region to another. 

The most common type of anal cancer, accounting for almost 90 percent of cases in the US, is squamous cell carcinoma. These are tumors that start in the thin, flat cells that are found in the anal canal and around the anal verge, but which can spread more deeply into the tissues if left unchecked. 


There are other, rarer types as well, and sometimes doctors will detect pre-cancerous changes that might need to be treated to prevent them from turning into full-blown cancer. 

It’s also possible to develop benign tumors of the anus. For example, anal warts are growths in or around the lower anal canal caused by certain types of human papillomavirus (HPV). While warts in and of themselves are not cancerous, having this condition does put someone at greater risk of developing anal cancer in the future.

Other risk factors include HIV infection, a suppressed immune system, and smoking tobacco. 

What are the symptoms of anal cancer?

The symptoms of anal cancer can mimic other conditions, making them tricky to spot. Sometimes, there may be no symptoms at all. However, if you do experience any of these signs, you should get checked out by a doctor to rule out anything more serious.

  • Bleeding from the rectum. This is usually minor and can easily be mistaken for hemorrhoids (piles). You might see a small amount of blood on the paper after going to the toilet. 
  • Itching or pain around the anus.
  • A lump or mass near the anus.
  • Changes in bowel habits. Any changes in the consistency or frequency of your poops should be mentioned to your doctor, but one that you might not have thought about is a “narrowing” of the stool – literally, if your poops become more narrow, shaped like a pencil or even a ribbon. This can be a sign of an obstruction somewhere in the colon, rectum, or anus, so should be checked out.
  • Discharge from the anus or loss of bowel control (fecal incontinence).
  • Swollen lymph nodes near the anus or in the groin.

Testing for anal cancer

Sometimes, anal cancer will be detected during a routine physical or while your doctor is performing another procedure, such as removing a hemorrhoid. More often, a diagnosis is made after a patient reports one or more of the symptoms listed above, which is why it’s so important to get checked sooner rather than later.

There are a few different tests that specialist cancer or gastrointestinal doctors can perform to diagnose anal cancer and check what stage it is at. One of the first things will likely be a physical exam, where a doctor will feel around the anus and rectum for lumps or any other changes.

If cancer is suspected, an anoscopy can be performed. This allows doctors to get a clearer view of the inside of the anus, as well as take biopsy samples for analysis in the lab. There are also various other imaging methods that can be used, such as magnetic resonance imaging (MRI) and positron emission tomography (PET) scans, to help find cancer, see if it has spread, and check if treatment is working.

Anal cancer treatment

There are treatment options for anal cancer. It all depends on the type of cancer, where it is located, and how early it has been caught.


The most common treatment is a combination of radiotherapy and chemotherapy. This is particularly the case when the cancer has not spread to other parts of the body. This combined treatment is called chemoradiotherapy or chemoradiation. 

The chemotherapy part of the treatment may involve more than one drug, and it’s also common for people to be given other drugs alongside that which can help counteract some of the side effects. Some drugs can be given using a portable pump that the patient can take home with them, while others may involve a short stay in hospital.

Radiotherapy is performed over a period of several weeks. The most common type used for anal cancer treatment involves a focused beam of radiation being directed at the cancerous cells from outside the body. Modern techniques, such as intensity-modulated radiation therapy, allow for more precise targeting, reducing the damage to surrounding healthy cells and helping to minimize some of the side effects. 

In some cases, like when chemoradiotheraphy does not completely cure the cancer, surgery may be needed. The anus, rectum, and part of the colon can be removed in a procedure called abdominoperineal resection. In these cases, the patient will no longer be able to pass feces in the usual way, so a colostomy will be required. This is where an artificial opening to the colon, called a stoma, is created on the surface of the abdomen, so that waste products can pass out into a specially designed bag that fits over the opening.


Between receiving a difficult diagnosis and grappling with challenging treatments and side effects, cancer can also take a significant toll on patients’ mental health. It’s common for people undergoing cancer treatment to need support with this, be that from friends and family, or from mental health professionals.

What’s the outlook?

Anal cancer remains rare, particularly in people under 35. On average, people are diagnosed with anal cancer in their early 60s. The American Cancer Society estimates that there will be around 9,760 new cases of anal cancer in the US in 2023, and the incidence has been increasing for several years now.

Thankfully, treatment for anal cancer is often very successful if it is caught early, and the treatments are improving all the time. For cancer that has not spread outside of the anal area, the 5-year relative survival rate has been given as 83 percent.

No one enjoys talking about their poop, and it can sometimes be tempting to ignore a worrying symptom rather than having what you might think is an embarrassing conversation with your doctor. But it’s important to remember that cancer can arise pretty much anywhere in the body – even the parts we tend not to talk about. 


All the symptoms we mentioned can be signs of other, less scary things. But, if it does turn out to be cancer, getting it checked early could make all the difference when it comes to treatment and – hopefully – a cure.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.  

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current. 


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