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Medically reviewed by C.H. Weaver M.D. 6/2021

Anal cancer is relatively uncommon. The American Cancer Society estimates about 8,800 individuals will be diagnosed in 2021. The number of individuals developing anal cancer has been rising for many years and the risk of being diagnosed with anal cancer during one’s lifetime is about 1 in 500. Current treatment for anal cancer can be very effective especially when then cancer is detected early.1

Anal cancer starts in the anus, which is the opening at the lower end of the intestines. This opening is connected to the rectum by the anal canal. The anal canal is about an inch and a half long. It goes from the rectum to the anal verge where the canal meets the outside skin at the anus. Most anal cancers start in the squamous cells in the inner lining of the anal canal called the mucosa.

The anal canal is surrounded by a sphincter which is a circular muscle that keeps feces from coming out until it relaxes during a bowel movement. Anal cancers are often divided into two groups, which are sometimes treated differently:

  • Cancers of the anal canal (above the anal verge)
  • Cancers of the anal margin (below the anal verge)

Anal cancers can also begin in glands that make mucus, which acts as a lubricating fluid. These are called adenocarcinomas and a treated like colo-rectal cancer. This content focuses on invasive anal squamous cell carcinomas, which account for the vast majority of anal cancers.1-3

Symptoms & Signs of Anal Cancer

Early-stage anal cancer may produce no signs or symptoms. Symptoms of more advanced anal cancer may include the following.1-3

  • Bleeding from the anal area
  • Pain or pressure in the anal area
  • Itching or discharge from the anus
  • A lump or swelling near the anus
  • A change in bowel habits or change in the diameter of the stool
  • Having these symptoms does not mean that an individual has anal cancer because these symptoms can be caused by other health conditions. If you have any of these symptoms however they should be brought to the attention of a health professional.


Anal cancer begins when healthy cells acquire a genetic change (mutation) that causes them to turn into abnormal cells. Although it isn’t clear what causes anal cancer the human papilloma virus (HPV) may play a role.2

Risk factors

A risk factor is anything that increases a person’s chance of developing cancer. Risk factors can influence the development of cancer but most do not directly cause cancer. Many individuals with risk factors will never develop cancer and others with no known risk factors will.

Although most anal cancers develop sporadically, which means for no known reason the following factors may raise a person’s risk for developing anal cancer:

Risk factors for anal cancer include:

  • Human Papilloma Virus.
  • Multiple sexual partners. The greater the number of sexual partners the greater the greater your chance of acquiring HPV.
  • Early sexual activity. Having sex at an early age increases the risk of HPV.
  • A weak immune system. Individuals are more likely to develop anal cancer if their immune system is weakened by another health condition and infection with HPV.[1],[2]

Diagnosis & Tests for Anal Cancer

When diagnosed with anal cancer further tests are necessary to determine the extent of spread (stage) of the cancer. Cancer’s stage is a key factor in determining the best treatment.

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In addition to a physical examination, the following tests may be used to diagnose and stage anal cancer:

Digital Rectal Examination (DRE): During a DRE the doctor inserts a gloved finger into the anus to feel for lumps or other abnormalities.

Anoscopy: If the doctor feels a suspicious area during a DRE, an anoscopy may be performed to take a closer look at the area. An anoscopy allows the doctor to see inside the body with a thin, lighted, flexible tube called an anoscope. An individual is typically sedated as the tube is inserted into the anus and/or rectum.

Biopsy: A biopsy is the removal of a small amount of tissue for examination under a microscope. A definite diagnosis of cancer can only be confirmed with a biopsy to look for cancer cells in the sample. The type of biopsy performed will depend on the location of the suspected cancer.

Ultrasound: An ultrasound uses sound waves to create a picture of the internal organs. In an anal ultrasound, an ultrasound wand is inserted into the anus to get the pictures.

X-ray: An x-ray is way to create a picture of the structures inside of the body using a small amount of radiation.

Computed Tomography (CT) Scan: A CT scan is a technique for imaging body tissues and organs, during which X-ray transmissions are converted to detailed images, using a computer to synthesize X-ray data. A CT scan is conducted with a large machine positioned outside the body that can rotate to capture detailed images of the organs and tissues inside the body.

Magnetic Resonance Imaging (MRI): MRI uses a magnetic field rather than X-rays, and can often distinguish more accurately between healthy and diseased tissue than a CT. An MRI gives a better picture of cancer located near bone than does CT, does not use radiation, and provides pictures from various angles that enable doctors to construct a three-dimensional image of the cancer.

Positron emission tomography (PET): Positron emission tomography scanning is an advanced technique for imaging body tissues and organs. One characteristic of living tissue is the metabolism of sugar. Prior to a PET scan, a substance containing a type of sugar attached to a radioactive isotope (a molecule that emits radiation) is injected into the patient’s vein. The cancer cells “take up” the sugar and attached isotope, which emits positively charged, low energy radiation (positrons) that create the production of gamma rays that can be detected by the PET machine to produce a picture. If no gamma rays are detected in the scanned area, it is unlikely that the mass in question contains living cancer cells.

Bone Scan: A bone scan is used to determine whether cancer has spread to the bones. Prior to a bone scan a small amount of radioactive substance is injected into a vein. This substance travels through the bloodstream and collects in areas of abnormal bone growth. An instrument called a scanner measures the radioactivity levels in these areas and records them on x-ray film.

Genomic or Bio-marker Testing-Precision Cancer Medicine

The purpose of precision cancer medicine is to define the genomic alterations in the cancers DNA that are driving that specific cancer. Precision cancer medicine utilizes molecular diagnostic & genomic testing, including DNA sequencing, to identify cancer-driving abnormalities in a cancer’s genome. Once a genetic abnormality is identified, a specific targeted therapy can be designed to attack a specific mutation or other cancer-related change in the DNA programming of the cancer cells. Precision cancer medicine uses targeted drugs and immunotherapies engineered to directly attack the cancer cells with specific abnormalities, leaving normal cells largely unharmed.

By testing a cancer for specific unique biomarkers doctors can offer the most personalized treatment approach utilizing precision medicines.


  1. American Cancer Society. Cancer Facts & Figures 2020.
  2. National Cancer Institute Fact Sheet. Human Papillomaviruses and Cancer: Questions and Answers.
  3. Anal Cancer