Anal cancer is a disease in which malignant (cancer) cells form in the tissues of the anus.
The anus is the end of the large intestine, below the rectum, through which stool (solid waste) leaves the body. The anus is formed partly from the outer, skin layers of the body and partly from the intestine. Two ring-like muscles, called sphincter muscles, open and close the anal opening to let stool pass out of the body. The anal canal, the part of the anus between the rectum and the anal opening, is about 1½ inches long.
The skin around the outside of the anus is called the perianal area. Tumors in this area are skin tumors, not anal cancer.
Being infected with the human papillomavirus (HPV) can affect the risk of developing anal cancer.
Risk factors include the following:
- Being over 50 years old.
- Being infected with human papillomavirus (HPV).
- Having many sexual partners.
- Having receptive anal intercourse (anal sex).
- Frequent anal redness, swelling, and soreness.
- Having anal fistulas (abnormal openings).
- Smoking cigarettes.
Possible signs of anal cancer include bleeding from the anus or rectum or a lump near the anus.
These and other symptoms may be caused by anal cancer. Other conditions may cause the same symptoms. A doctor should be consulted if any of the following problems occur:
- Bleeding from the anus or rectum.
- Pain or pressure in the area around the anus.
- Itching or discharge from the anus.
- A lump near the anus.
- A change in bowel habits.
Tests that examine the rectum and anus are used to detect (find) and diagnose anal cancer.
The following tests and procedures may be used:
- Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient's health habits and past illnesses and treatments will also be taken.
- Digital rectal examination (DRE): An exam of the anus and rectum. The doctor or nurse inserts a lubricated, gloved finger into the lower part of the rectum to feel for lumps or anything else that seems unusual.
- Anoscopy: An exam of the anus and lower rectum using a short, lighted tube called an anoscope.
- Proctoscopy: An exam of the rectum using a short, lighted tube called a proctoscope.
- Endo-anal or endorectal ultrasound: A procedure in which an ultrasound transducer (probe) is inserted into the anus or rectum and used to bounce high-energy sound waves (ultrasound) off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram.
- Biopsy: The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. If an abnormal area is seen during the anoscopy, a biopsy may be done at that time.
Certain factors affect the prognosis (chance of recovery) and treatment options.
The prognosis (chance of recovery) depends on the following:
- The size of the tumor.
- Where the tumor is in the anus.
- Whether the cancer has spread to the lymph nodes.
- The treatment options depend on the following:
- The stage of the cancer.
- Where the tumor is in the anus.
- Whether the patient has human immunodeficiency virus (HIV).
- Whether cancer remains after initial treatment or has recurred.
After anal cancer has been diagnosed, tests are done to find out if cancer cells have spread within the anus or to other parts of the body.
The process used to find out if cancer has spread within the anus or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment. The following tests may be used in the staging process:
CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography. For anal cancer, a CT scan of the pelvis and abdomen may be done.
Chest x-ray: An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.
Endo-anal or endorectal ultrasound: A procedure in which an ultrasound transducer (probe) is inserted into the anus or rectum and used to bounce high-energy sound waves (ultrasound) off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram.
There are three ways that cancer spreads in the body.
The three ways that cancer spreads in the body are:
- Through tissue. Cancer invades the surrounding normal tissue.
- Through the lymph system. Cancer invades the lymph system and travels through the lymph vessels to other places in the body.
- Through the blood. Cancer invades the veins and capillaries and travels through the blood to other places in the body.
When cancer cells break away from the primary (original) tumor and travel through the lymph or blood to other places in the body, another (secondary) tumor may form. This process is called metastasis. The secondary (metastatic) tumor is the same type of cancer as the primary tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer.
The following stages are used for anal cancer:
Stage 0 (Carcinoma in Situ)
In stage 0, abnormal cells are found in the innermost lining of the anus. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called carcinoma in situ.
In stage I, cancer has formed and the tumor is 2 centimeters or smaller.
In stage II, the tumor is larger than 2 centimeters.
In stage IIIA, the tumor may be any size and has spread to either:
- lymph nodes near the rectum; or
- nearby organs, such as the vagina, urethra, and bladder.
In stage IIIB, the tumor may be any size and has spread:
- to nearby organs and to lymph nodes near the rectum; or
- to lymph nodes on one side of the pelvis and/or groin, and may have spread to nearby organs; or
- to lymph nodes near the rectum and in the groin, and/or to lymph nodes on both sides of the pelvis and/or groin, and may have spread to nearby organs.
In 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
Recurrent anal cancer is cancer that has recurred (come back) after it has been treated. The cancer may come back in the anus or in other parts of the body.