According to the American Cancer Society, having cancer of the anus is a fairly rare occurrence in the United States. This is especially notable when compared to colorectal cancer, a type that occurs nearby in the rectum or colon. While the two are similar, they have different risk profiles and typical treatment regimens. Yet even though anal cancer is relatively rare, the number of cases and deaths has been rising consistently over many years. Fortunately, though, the treatment options have also become more effective. 

What is Anal Cancer?  

The basic definition of anal cancer is abnormal cell growth in the anus, which is the name for the external opening at the base of the rectum and the final section of the digestive tract where defecation occurs. As noted above, anal cancer is sometimes inaccurately conflated with colorectal cancer because of their close proximity. Incidences of colorectal cancer are specifically located in either the colon or the rectum, whereas anal cancer arises specifically in the anus.

As food waste in the form of feces makes its way through the large intestine, water is absorbed until the stool (under normal circumstances) becomes firm. Stools are then held in the rectum until the body is ready to evacuate. At that point, two rings of muscle in the anus, known as the internal and external anal sphincters, act to control the actual mechanism of defecation. The anus is also the site of the dentate line, the transition point between the mucosa lining of the rectum and the squamous epithelial cells that surround the opening of the anal canal; this is also why anal cancer can sometimes be known as squamous cell cancer or squamous cell carcinoma.  

Each year in the United States, nearly 10,000 new cases of anal cancer are diagnosed and around 1500 deaths are reported. While this is a relatively small number of cases, these figures have been rising in recent years for unknown reasons. This type of cancer is exceedingly rare in people under 35, and it is more likely to occur in people older than 55. For reasons that are still not understood, white women and black men tend to be more likely to develop anal cancer. The average five year survival rate is 68%.      

Types of Anal Cancer

Though the anus and anal canal represent a small area of the body, they are complex structures with different types of cells. Indeed, anal cancers can be categorized into two types, depending on where they first develop in relation to the anal verge; this term refers to the transition point between the anus it self and the perianal skin that surrounds it. The two basic categories of anal cancer are cancers of the anal canal above the anal verge, and cancers of the perianal skin below the anal verge. 

Nearly 9 out of 10 cases of anal cancer are considered squamous cell carcinomas due to mutations that occur in the squamous cells in either anal canal or the perianal skin. In some situations, a squamous cell carcinoma of the perianal skin will be treated as a type of skin cancer rather than anal cancer. However, the vast majority of anal cancer cases first develop in the anal canal itself. And in either case the abnormal growth is identified when mutated squamous cells grow beyond the surface and deeper into the anal lining. A much more rare form of anal cancer is adenocarcinomas; because they develop closer to the rectum, they are often treated as other rectal cancers are treated. 

What Causes Anal Cancer?     

As with many types of cancer, the precise cause of anal cancer is not fully known. There are known risk factors that make a person more likely to develop it, but there have also been cases where no risk factors were present prior to the onset. Of the identified risk factors, some are fixed and unchangeable while others can be mitigated through lifestyle changes. Below are some of the most common risk factors for anal cancer: 

  • HPV Infection: Being infected by the human papillomavirus (HPV) is the most common cause of anal cancer and specifically squamous cell anal cancers. HPV is also a major risk factor of cervical cancer and some other types of cancer. HPV only infects cells along the surface of the skin or those lining the genitals or parts of the digestive tract, but this means that it can be spread through skin-to-skin contact and sexual activity. HPV infections are fairly common and are usually cleared naturally by the body, but a chronic infection can eventually lead to anal cancer. 
  • HIV Infection: The human immunodeficiency virus (HIV) is well known for causing the disease known as AIDS, but a person who has an HIV infection is also more likely to develop anal cancer. Though the exact connection is not known, the compromised immune function that is a characteristic result of HIV can make the body more susceptible to anal cancer. 
  • Anal Warts: Some HPV infections can cause genital or anal warts, which are abnormal outgrowths on the skin. While these warts themselves are not cancerous, if left untreated they can become cancerous. Additionally, just having the warts makes a person more likely to be infected by subtypes of HPV that cause anal cancer. 
  • Sexual Activity: Both HPV and HIV can be contracted through various kinds of sexual activity and is also more likely when having multiple sexual partners. Becoming infected with either virus can lead to anal cancer as noted above. Receptive anal sex is another sexual factor that increases the risk of developing anal cancer because it increases the chance of getting an HIV or HPV infection.
  • Smoking: The carcinogens in tobacco products are known for causing lung cancer, but these harmful chemicals can get into the bloodstream and potentially cause cancer in other parts of the body as well. Smoking is believed to be a risk factor for anal cancer as well because it reduces the immune system’s ability to fight off HPV.  
  • Reduced Immunity: Whether through an HIV infection, smoking, or a number of other causes, a weakened immune system can increase the risk of anal cancer. This includes people who must be on medication that reduces immune function as a side effect.  

Symptoms of Anal Cancer      

Not all incidents of anal cancer are marked by specific symptoms. It is for this reason that sometimes it’s harder to detect anal cancer early. Sometimes symptoms don’t even appear until late stages, and sometimes the symptoms may even mimic other gastrointestinal conditions. In general, though, it is important to keep in mind the following potential symptoms: 

  • minor bleeding from the rectum (similar to hemorrhoids
  • lump or growth around the anal opening
  • rectal itching
  • changes in bowel movements 
  • narrower than normal stools
  • pain or a feeling of fullness in the anal area
  • abnormal discharge 
  • loss of bowel control 
  • swollen lymph nodes
  • anal intraepithelial neoplasia (a type of precancerous lesion)

Treatment Options for Anal Cancer

Like other cancers, the kind of anal cancer treatment selected is dependent on where it starts and how far it has spread upon diagnosis. The overall size of any cancerous masses will also inform some treatment options. Below are the main treatment options available: 

  • Surgery: Early stage cases of anal cancer can often be treated by simply removing the affected tissue (abdominoperineal resection, for example). Once removed, no further treatment is necessary in many cases.
  • Radiation Therapy: In radiation therapy, high energy X-rays or particle beams are aimed at the cancerous cells to kill them. This is also sometimes used in conjunction with chemotherapy.
  • Chemotherapy: Chemotherapy involves introducing anti-cancer drugs into the body through swallowing a pill or injection into a vein. Once in the bloodstream, these chemicals are able to kill cancer cells almost anywhere in the body.   

When to See a Doctor 

Fortunately, anal cancer is still very rare in the United States, and for this reason it isn’t usually screened for. But overall good digestive health starts with being mindful of symptoms and any changes to bowel habits. At Cary Gastro, we are dedicated to providing excellent digestive healthcare. If you have been experiencing any of the symptoms described here, or have noticed any other digestive system-related problems, please contact us to request an appointment.