Colorectal surgeon Dr. Georgios Karagkounis, smiling and wearing a white doctors' coat, treats anal cancer patients in Manhattan and Brooklyn.

MSK’s GUIDE TO

Anal Cancer Diagnosis, Types & Stages

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Overview

At MSK, treatment for anal cancer starts with a correct diagnosis. We’re here to help you take the first steps toward getting the best cancer care.

You may be reading this because you’re worried you may have anal cancer. Maybe you’re waiting for test results. Or perhaps you or someone you care about just learned they have anal cancer.

This guide will help you understand how anal cancer is diagnosed and what your diagnosis means. Learning as much as you can may help you feel ready to talk with doctors about your care.

Colorectal surgeon Dr. Philip Paty talks with his MSK colorectal cancer patient in New York City.

The diagnosis process

Anal cancer often is found after there are symptoms. Your doctor may do an exam and other tests to diagnose anal cancer.

Colorectal surgeon Dr. Emmanouil Pappou, wearing scrubs in a hallway, sees cancer patients in New York City and New Jersey.

Understanding your diagnosis

Your diagnosis most often will describe where the cancer started, its type, and if it has spread. We use this information to create your care plan.

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The diagnosis process

How is anal cancer diagnosed?

We diagnose anal cancer in a few ways. It’s often found during a procedure for another problem, such as a hemorrhoid.

Anal cancer often is found after there are symptoms. If your healthcare provider thinks you may have anal cancer, they may ask you to see an expert in colorectal cancers. They can order tests to confirm if you have anal cancer.

If you have signs or symptoms of anal cancer, your diagnosis process may look like this:

Health record: If you have symptoms, your primary care provider will review your health record. They’ll ask questions to find out if you have any anal cancer risk factors. They may send you to an expert, such as a gastroenterologist. A gastroenterologist (GAS-troh-EN-teh-RAH-loh-jist) is a doctor with special training in the gastrointestinal (GI) system.
Digital rectal exam and physical exam: Your doctor will use a finger to feel for any tumors or areas that are not normal in your anus and rectum. They may check other parts of your body for health problems that are causing your symptoms. Your healthcare provider may order diagnostic tests. If you have a cervix, they may give you a Pap test or pelvic exam.
Endoscopic (en-doh-SKAH-pik) tests: These tests use a flexible tube with a camera on the end to look inside the anus and rectum. Examples are a colonoscopy, anoscopy, proctoscopy (rigid sigmoidoscopy), and flexible sigmoidoscopy  (sig-MOY-DOS-koh-pee). They’ll look for lumps or tissue that does not look normal. 
Biopsy: A biopsy is a procedure to remove a small piece of tissue. For anal cancer, the biopsy may be done with anesthesia (medicine to make you sleep). A pathologist is a doctor who uses a microscope to diagnose disease. They’ll examine your tissue sample under a microscope to see if it has cancer cells. If they find cancer, you will have tests to find the cancer type, such as imaging tests.
Imaging Tests: If cancer cells are found in your biopsy tissue sample, your doctor will order imaging tests. They may include a computed tomography (CT) scan, magnetic resonance imaging (MRI), and positron emission tomography (PET) scan. These tests can show if the cancer has spread to other parts of your body.

At MSK, our goal is to get you through this challenging time and back to your life. We’ve treated thousands of patients who, like you, came in with anxiety, hopes, and uncertainty about the future.

Colorectal surgeon Georgios Karagkounis treats anal cancer at MSK in Manhattan and Brooklyn.

Understanding your diagnosis

Learning you have anal cancer can be overwhelming. You’ll hear many medical terms you've never heard before. We’re here to help you understand what they mean and why they matter.  

The information in your anal cancer diagnosis describes important details about the type of cancer you have. Your doctors use that information to create the best plan of care for you. 

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Here is some of the information your diagnosis may include:

Where the anal cancer started

Anal cancer starts in the anus’ tissues or in the cells of the inside lining of the anus.

Where the anal cancer started

Anal cancer often starts in the anus’ tissues or the lining of the anal canal.

The anal canal connects the anus to the rectum. The anal canal is a tube about 1.5 to 2 inches (3.8 to 5 cm) long and includes the sphincter muscles. The inside lining of the anal canal is called the mucosa.

The anal verge is where the anal canal connects to the outside skin of the anus. The perianal skin is outside and around the anal verge. 

Anal cancers are grouped by where they start, in the anal canal or the perianal skin.  

Most anal cancers start in the squamous (SKWAY-mus) cells in the inner lining of the anal canal. Anal cancer begins when healthy cells change and grow out of control.  

If the anal cancer is spreading

Some anal tumors stay in the place where they started, but others can metastasize (spread) to other areas.

If the anal cancer is spreading

Anal cancer often just stays within the anus. If anal cancer is not treated, it can spread to other organs, such as the liver and lungs.

Metastatic (meh-tuh-STA-tik) anal cancer means the cancer cells have spread beyond the anus to other organs. It’s also called advanced anal cancer or stage 4 anal cancer.

If it spreads, anal cancer most often spreads to the lungs and liver. That’s because 2 large blood vessels connect the blood supply from the intestines to lungs and liver.

Anal cancer can also spread to the lymph nodes, small organs that are part of the immune system.

The stage, which explains the tumor’s size, location, and how far it has spread

The stage tells us how advanced the anal cancer is and guides treatment. There are 5 stages, from 0 to 4 (0 to IV). The lower the number, the less the anal cancer has spread.

The stage, which explains the tumor’s size, location, and how far it has spread

The stage tells us how advanced the cancer is and guides treatment.

There are 5 stages, from 0 to 4 (0 to IV). The lower the number, the less the cancer has spread.

Stage 0

There are cancer cells. The tumor cells have not yet spread. Stage 0 is very early cancer that’s only in the top layer of the lining of the anus.
Stage 1

There is 1 small tumor and the anal cancer has not spread outside the anus.
Stage 2

The tumor has grown larger than 2 centimeters.
Stage 3

The tumor has not spread, or has spread to 1 or more nearby lymph nodes.
Stage 4

Distant spread: Cancer has metastasized (spread) outside the place where it started. It’s spread to other parts of the body, such as lymph nodes, the liver, or lungs.
Learn more about anal cancer stages

Gastroenterologist Dr. Robin Mendelsohn, standing in an MSK hallway, treats colorectal cancer patients in New York City.

When a person is diagnosed with colorectal cancer, it's overwhelming. They don't always know what questions to ask. That's where the center comes in.

Gastroenterologist Dr. Robin Mendelsohn, co-director, the Center for Young Onset Colorectal and Gastrointestinal Cancer

Learn more

MSK Recommends Bring these questions to your next appointment

When you learn you have anal cancer, you’ll have many questions for your cancer doctor at your first visit. Talking about treatment options with your doctor can help you feel better prepared to make decisions about your care.

What type of anal cancer do I have, and what stage is it?  
Did I have all the scans I need to learn the stage?   
What genetic testing do you offer for anal cancer?

What are the best treatment options for the type and stage of anal cancer I have?   
When can I start treatment?   
Can I get treatment at MSK locations close to my home?    
What are the risks and side effects of anal cancer treatment?   
Are there new anal cancer drugs I can try?   
Will I need more tests before treatment starts?  
What experience do you have in treating my type of cancer?   
How will MSK help me recover after treatment?   
Will I get side effects from treatment? How can I manage them?

Types of anal cancer

What are the types of anal cancer?

There are a few types of anal cancer. We’re experienced in treating them all, from the most common to the most rare. This information describes each kind of anal cancer and explains how we classify (sort) them.

Most people who are diagnosed with anal cancer have a type called squamous cell carcinoma. There are other rarer tumor types, too.

Squamous (SKWAY-mus) cell carcinoma (KAR-sih-NOH-muh) is the most common type of anal cancer. About 9 out of every 10 anal cancers start in squamous cells that line the outer layer of the anus. If found early, squamous cell carcinoma often is very treatable.

Adenocarcinoma (A-deh-noh-KAR-sih-NOH-muh) is in the upper part of the anus. Adenocarcinoma anal cancer forms in glandular tissue, which lines some organs.

Basal cell carcinoma is in the skin around the anus and is a very rare type of anal cancer. Surgery is the most common treatment for basal cell carcinoma in the anus.

Melanoma is a very rare type of anal cancer that often is found at a later stage. It can be very hard to spot.

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Anal cancer stages 0, 1, 2, 3, and 4

The cancer stage describes traits such as the tumor’s size, whether it spread, and where it spread. Staging tells us how advanced the cancer is. The stage guides the choice of treatment.

There are 5 stages of anal cancer, from 0 to 4 (0 to IV). The lower the number, the less the cancer has spread.

Knowing the stage of the cancer helps you and your doctor decide on the best treatment options for you.

The stage is based on:

The size and location of the original tumor (also called the primary tumor).
If the cancer has spread to nearby lymph nodes.
If the cancer has spread to other parts of the body, such as the lungs or liver.

Your doctor may use letters and numbers from the TNM system to describe the stage: 

T  is the size of the tumor.  
N  is whether the cancer has spread to the lymph nodes.  
M  is whether the cancer has  metastasized  (spread) to other areas.

N0 means cancer is not in lymph nodes, while N1, N2 or N3 means it’s spread to nodes. M0 means cancer has not spread, while M1 means it’s spread to distant organs, muscles, or bones.

What are the stages of anal cancer?

Stage 0

Stage 0 anal cancer is also called carcinoma in situ (in-SY-too). In situ means “in its original place.”
Stage 0 is when there are abnormal (not normal) cells in the anus. These cells can become cancer. The cancer is noninvasive. That means there are no signs the cancer has spread to healthy tissue around it.
In the TNM staging system: T0, N0, M0. 
Stage 1
Stage 2

Stage 2 anal cancer tumors are larger than 2 centimeters but have not spread.
There’s a stage 2A and 2B.
In stage 2A, the tumor is larger than 2 centimeters but smaller than 5 centimeters. It’s between the size of a peanut and a grape.
In the TNM staging system: T2, N0, M0.
In stage 2B, the tumor is larger than 5 centimeters. It’s spread to lymph nodes near the rectum.
In the TNM staging system: T1 to T2, N1, M0.
Stage 3

Stage 3 anal cancer may have spread to nearby lymph nodes or other organs.
There’s a stage 3A, 3B, and 3C.
In stage 3A, the tumor is larger than 5 centimeters. It has not spread to nearby lymph nodes or other parts of the body.
In the TNM staging system: T3, N0, M0.
Or, the anal cancer tumor is larger than 5 cm and has spread to lymph nodes near the rectum.
In the TNM staging system: T3, N1, M0.
In stage 3B, the tumor is any size. The tumor has spread to nearby organs, such as the vagina, urethra, bladder, or prostate gland. It has not spread to nearby lymph nodes.
In the TNM staging system: T4, N0, M0.
In stage 3C, the tumor is any size. The tumor has spread to nearby organs, such as the vagina, urethra, bladder, or prostate gland. It has spread to lymph nodes near the rectum.
In the TNM staging system: T4, N1, M0.
Stage 4

Majiel Baker, with her son at the beach, traveled from upstate New York for treatment at MSK.

Everyone is really invested in what’s best for you. You don’t feel like you’re just a number walking through a door at a local hospital. It’s worth the travel and the time. It’s just a wonderful feeling. 

Majiel Baker says “MSK was the best decision I could have made.” She is among some 5,000 people who travel more than 150 miles for cancer care at MSK each year.   

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Last updated December 2, 2025

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