Overview
The anal canal
The anal canal
The anal canal is a tube at the end of the rectum that measures 1 1/2 inches in length (about 4 centimeters). Muscles called sphincters surround the anal canal. The sphincters relax to allow waste to leave the body.
Anal cancer is a growth of cells that starts in the anal canal. The anal canal is a short tube at the end of the rectum. Anal cancer may appear like a firm lump or bump, an open sore or ulcer, or a thickened, wartlike area of skin.
For most people, anal cancer develops after a long-term infection with a high-risk type of human papillomavirus (HPV) in the anal area.
Anal cancer can cause symptoms such as rectal bleeding, blood in the stool and anal pain. As it grows, it might cause a growth or lump that constantly bleeds, itches, or hurts. These symptoms might be mistaken for hemorrhoids. It is important to have a healthcare professional check the area and take a tissue sample, called a biopsy, from any growth to make a diagnosis.
Anal cancer is fairly rare, with about 0.2% of people developing it during their lifetime. Anal cancer is usually treated by a team of cancer specialists. Treatment of anal cancer has evolved over time. Today, anal cancer treatment options include chemotherapy, radiation therapy and surgery in some cases.
Types of anal cancer
The most common type of anal cancer is squamous cell carcinoma (SCC). It begins in the thin, flat squamous cells that line the anal canal and the ring of skin around the outside of the anus. Most cases are linked to human papillomavirus (HPV) infection, especially high-risk HPV types 16 and 18. A common treatment for SCC that has not spread includes concurrent chemotherapy and radiation.
Other types of anal cancer include:
- Adenocarcinoma. This uncommon type starts in the anal glands that produce mucus. Adenocarcinoma behaves like rectal cancer and is usually treated with surgery plus radiation and chemotherapy.
- Neuroendocrine carcinoma. This rare and highly aggressive cancer develops from neuroendocrine cells found in the anal canal. It can appear as either a small cell or large cell type. Both types tend to grow and spread quickly. This rare cancer is often treated with chemotherapy, radiation and sometimes surgery, depending on the size of the tumor.
- Basal cell carcinoma. This very rare cancer arises from the basal cells of the skin around the anus, known as the perianal region. Most people can be successfully treated with local surgical removal.
- Melanoma. This rare form of anal cancer is aggressive and develops from the pigment-producing cells in the anal or perianal skin, called melanocytes. Treatment often includes surgery and immunotherapy.
Symptoms
Anal cancer may begin without any noticeable symptoms. If symptoms appear, they may include:
- Bleeding from the anus or rectum.
- Blood in the stool.
- Pain in the area of the anus.
- A growth in the anal canal.
- Anal itching.
- Changes in stool appearance and bowel habits, including thinner stools or constipation.
- Having a feeling of fullness or needing to go to the bathroom, even after going to the bathroom.
When to see a doctor
Make an appointment with a doctor or other healthcare professional if you have any symptoms that worry you or if they are not going away. Typically a healthcare professional looks for any hemorrhoids, lumps, tears called fissures, or lesions, that need to be tested.
Causes
Anal cancer happens when cells in the anal canal develop changes in their DNA. A cell's DNA holds the instructions that tell a cell what to do. In healthy cells, DNA gives instructions to grow and multiply at a set rate. The instructions tell the cells to die at a set time. In cancer cells, the changes tell the cancer cells to make many more cells quickly. Cancer cells can keep living while healthy cells would die. This results in too many cells.
The cancer cells might form a mass called a tumor. The tumor can grow to invade and destroy healthy body tissue. In time, cancer cells can break away and spread to other parts of the body. When cancer spreads, it's called metastatic cancer.
Most anal cancers are caused by human papillomavirus (HPV). This is a common virus that's passed through sexual contact. For most people, the virus never causes problems. It usually goes away on its own. For some, though, the virus can cause changes in the cells that may lead to cancer.
Risk factors
Things that may increase the risk of anal cancer include:
- Being exposed to human papillomavirus (HPV). HPV is a common virus that's passed through sexual contact. For most people, it causes no problems and goes away on its own. For others, it causes changes in the cells that can lead to many types of cancer, including anal cancer.
- Increasing number of sexual partners. The greater your number of sexual partners, and the greater your partner's number of sexual partners, the greater your chance of acquiring HPV.
- Having anal sex. People who have receptive anal sex have an increased risk of anal cancer, as this activity may be linked to a higher chance of getting high-risk HPV.
- Smoking cigarettes. People who smoke cigarettes have an increased risk of anal cancer.
- Having a history of certain cancers. Those who have had penile, cervical, vulvar or vaginal cancer have an increased risk of anal cancer.
- Having a weak immune system. If the body's germ-fighting immune system is weakened by medicines or illness, there might be a higher risk of anal cancer. People with a weakened immune system include those taking medicines to control the immune system, such as after an organ transplant. Certain medical conditions, such as infection with human immunodeficiency virus (HIV), also can weaken the immune system.
- Having a history of sexually transmitted disease (STD). Several types of STDs, including anal warts, may increase your risk of anal cancer.
Complications
It is not common for anal cancer to spread to distant parts of the body. When it does spread, it tends to travel to the liver and lungs.
Prevention
Take steps to reduce your risk
There is no sure way to prevent anal cancer. To reduce your risk of anal cancer:
- Practice safer sex. Reduce your risk of anal cancer by taking measures to prevent STDs. This may include using a condom every time you have sex and limiting the number of sexual partners you have.
- Get the HPV vaccine. Getting a vaccination to prevent HPV infection may reduce your risk of anal cancer and other HPV-related cancers. Ask your healthcare team if an HPV vaccine is right for you.
- Don't use tobacco. If you don't use tobacco, don't start. If you currently use tobacco of any kind, talk with a healthcare professional about strategies to help you quit.
Ask about anal cancer screening
Screening tests can help detect anal cancer and precancerous cells that may one day develop into anal cancer. Healthcare professionals sometimes recommend screening for people with a high risk of anal cancer.
You might have a high risk of anal cancer if you:
- Have HIV.
- Have high-risk HPV.
- Are taking medicine to manage your immune system after an organ transplant.
- Have been diagnosed with precancerous cells in the penis, scrotum, cervix, vagina or vulva.
Screening tests might include:
- Anal Pap test. During an anal Pap test, a healthcare professional swabs cells from your anal canal. The cells are tested in a lab to check for cancer cells and cells that look like they could become cancerous.
- Anal HPV test. The anal HPV test involves testing cells from the anal canal for infection with HPV.
- Digital rectal exam. During a digital rectal exam, a healthcare professional inserts a gloved finger, coated with a water-based jelly, into the anus. The health professional feels the anal canal and rectum for growths or other signs of cancer.
Medical groups don't agree on who should have anal cancer screening and what tests should be used. Screening can detect anal cancer when it's small and easier to treat. But studies haven't proved that anal cancer screening can save lives. Talk about the benefits and risks of screening with your healthcare team.
Feb. 03, 2026