The Anus

The anus is the end of the large intestine, below the rectum. Stool passes through the anus to leave the body. The anus is made up partly of skin layers and partly from intestinal tissues. Two muscles, called sphincter muscles, control the passage of stool from the body. The anal canal, the part of the anus between the rectum and the anal opening, is about 1 ½ inches long.


Anal Cancer

Anal cancer makes up about 1-2 percent of all cancers of the large bowel and its outlet. Most are called squamous cell cancers. These arise from the outer layer of the skin. 

Anal cancer can spread into nearby tissues, such as the skin and sphincter muscle, or organs such as the prostate, bladder, or vagina. Tumor cells can spread via the lymph system to nearby or distant lymph nodes. They can also travel through the blood stream to distant organs. Anal cancer is highly treatable. It can most often be cured in the early stages. 

Risk Factors

Chronic anal inflammation is linked with anal cancer. Listed below are some of the risk factors.

  • Age – increased risk over age 50

  • Having multiple sexual partners

  • Human Papillomavirus (HPV)

  • Fissures, fistulas, hemorrhoids, and certain sexually transmitted diseases

  • Receptive anal sex

  • HIV 

  • Smoking cigarettes


Some of the symptoms of anal cancer are listed below. In the early stages there may be no symptoms. 

  • Bleeding or discharge from the anus or rectum

  • Pain or pressure in the rectal and anal area

  • Anal itching 

  • A lump near the anus

  • A change in bowel habits


The prognosis depends on certain factors. Some of these are listed below.

  • The size of the tumor. There are higher cure rates with smaller tumors.

  • Where the tumor is in the anus.

  • Whether the cancer has spread to the lymph nodes or distant organs.


These tests may be used to diagnose anal cancer. They also help us stage the disease which helps us make a treatment plan.

  • History and physical exam - a digital rectal exam, review of health habits, past illness, and treatments.

  • CT, PET CT, and /or MRI 

  • Anoscopy – an exam of the anus and lower rectum using a scope.

  • Proctoscopy – an exam of the rectum using a scope.

  • Transrectal or transanal ultra sound – a scope is placed into the rectum to do the ultrasound. This test helps to find out if the cancer has spread to local lymph nodes. 

  • Biopsy 

Stages of Anal Cancer

The stage of anal cancer describes whether the cancer has stayed within the anus, has spread to nearby or distant lymph nodes, or other organs. 

Stage 0 – cancer is found only in the inner lining of the anus. 

Stage I – the tumor is 2 cm or smaller.

Stage II – the tumor is larger than 2 cm.

Stage IIIA – the tumor has spread: 

  • to lymph nodes near the rectum, or

  • nearby organs.

Stage IIIB – the tumor has spread:

  •  to nearby organs and to lymph nodes near the rectum, or

  • to lymph nodes on one side of the pelvis or groin, and may have spread to nearby organs, or 

  • to lymph nodes near the rectum and in the groin, or lymph nodes on both sides of the pelvis or groin and may have spread to nearby organs.

Stage IV – the tumor may be any size and cancer may have spread to lymph nodes or nearby organs and has spread to distant parts of the body.

Recurrent anal cancer – cancer that has recurred (come back) after it has been treated. It may come back in the anus or in other parts of the body.


Radiation therapy is a cancer treatment that uses radiation to kill cancer cells. There are two types of radiation. 

  • External beam – uses a machine outside the body to send radiation to the cancer. 

  • Internal beam – uses a radioactive substance sealed in needles, seeds, wires, or catheters that are placed into or near the cancer. 

Chemotherapy (chemo) uses drugs to stop the growth of cancer cells. Chemo is a treatment that can reach the cancer cells throughout the body. It is often used with radiation.

Surgery is used if there is still disease after chemo and radiation. We may use surgery for small amounts of tumor, keeping sphincter muscle control. For more advanced disease, surgery may be required to remove the anus, rectum, and lymph nodes. You may need a colostomy.

Follow-Up Care

You need careful follow-up exams. Your team will talk with you about anoscopy, physical exams and imaging. You will continue with these follow ups for up to 5 years.

This information has been reproduced with permission of the National Cancer Institute. For more information please visit their website