Anal Cancer vs. Colon Cancer: How They Compare

Anal cancer and colon cancer both affect your lower digestive system, but they’re two very different conditions.

Anal cancer develops in the lowermost portion of your large intestine. Your anus only includes the short canal through which stool leaves your body.

Colon cancer, on the other hand, can develop in several areas of the large intestine. Cancers that develop in the first and longest section of the large intestine are classified as colon cancer, while cancers that develop in the lower portion before the anal canal are considered rectal cancer. Collectively, cancers of the large intestine are sometimes referred to as “colorectal cancers.”

Although the location is a big distinction between these types of cancer, there are also significant differences in the causes of these cancers and the symptoms they produce.

There’s some overlap in the symptoms of anal cancer and colon cancer, but the more specific differences can help you get an accurate diagnosis.

Causes and risk factors are the characteristics that are most different between these two conditions. Colon cancer can be caused by a number of genetic and lifestyle factors, but anal cancer is almost always linked to a viral infection.

Anal cancer

Infection with certain types of human papillomavirus (HPV) is believed to be the main cause of anal cancer. Although these viruses can be passed through any skin-to-skin contact, HPV-related cancers that develop in areas such as the anus, cervix, or vagina are often passed through sexual contact with an individual who has contracted HPV.

Other risk factors associated with anal cancer include:

• living with human immune deficiency virus (HIV)
• being more than 50 years old
• being a smoker
• practicing sex without a condom or barrier method
• having a history of other types of cancer, especially cervical, vulvar, or vaginal
• having anal warts
• having a weakened immune system
• taking medications that suppress your immune system

Colon cancer

The exact cause of colon cancer hasn’t been pinpointed, but there are a number of things that have been linked to this type of cancer.

Family history

• MUTYH-associated polyposis (MAP)
• Peutz-Jeghers syndrome
• Lynch syndrome (also known as hereditary nonpolyposis colon cancer or HNPCC)
• familialadenomatous polyposis (FAP)
• attenuated FAP (AFAP)
• Gardner’s syndrome

Genetic mutations that are linked to colon cancer can be passed through families. Some of the most common inherited genetic mutations that have been linked to colon cancer include:

Genetic changes

Genetic mutations can lead to several types of cancer, including colon cancer.

There’s a lot of variation in the genetic mutations associated with colon cancer that isn’t passed through families. Most of these mutations appear to begin in a gene called the APC gene.

In healthy people, this is the gene that would normally stop abnormal cell growth. In people with colon cancer this gene function doesn’t work, and cancer cells can reproduce rapidly.

The reason for these mutations is unclear, but a number of lifestyle choices (see below) are believed to play a role.

Inflammatory bowel diseases

People with inflammatory bowel diseases, such as Crohn’s disease or ulcerative colitis, have a greater risk of developing colon cancer in their lifetime.

Lifestyle choices

There are certain lifestyle choices that are linked to either the development of colon cancer or the gene mutations that lead to colon cancer. Some of the things that fall into this category include:

• lack of exercise
• a diet that lacks fruits and vegetables
• a low-fiber diet
• a high-fat diet
• eating a lot of processed meats
• heavy alcohol consumption
• cigarette smoking

The treatment strategies for anal and colon cancer are similar. Chemotherapy, radiation, or a combination of both treatments are often used, as well as surgery, to remove cancerous areas or tumors.

Depending on the location of the cancer, surgery could have different long-term outcomes. For example, colon cancer that affects an uncomplicated section of the large intestine can be removed, and the remaining ends can be attached to each other. You may need a colostomy to divert stools while this attachment heals, but the colostomy can usually be reversed later.

With anal cancer or certain rectal cancers, though, the muscles that help you maintain bowel control can be affected by surgery. If the section of your anal canal that contains your anal sphincter is removed, you may need a permanent colostomy.

The success of treatment and the chances of metastasis (cancer spread) or recurrence depends heavily on your specific type and stage of cancer.

Colon cancer

Colon cancers generally spread more easily than anal cancer, with metastasis happening in many cases before you’ve even had an initial diagnosis of colorectal cancer.

According to a 2016 study, about 20% of people with colon cancer already have metastasis to other areas of the body at the time of their initial diagnosis, and about 56% of people diagnosed with colorectal cancers die from the condition.

According to data from the 2012 to 2018 Surveillance, Epidemiology and End Results (SEER), the 5-year relative survival rate for people with colon cancer was 65.1%. The SEER data groups cancer statistics into localized, regional, and distant stages as follows:

Anal cancer

Anal cancers may not spread as quickly before the initial diagnosis. When metastasis does happen, local and regional spread to the lymph nodes in the groin, or to the rectum or perianal areas is most common. However, anal cancer is prone to recurrence or treatment resistance.

When anal cancer comes back after treatment, the risk of distant spread is higher. Common sites for metastasis in recurrent anal cancer are the liver and lungs.

According to SEER data from 2012 to 2018, the 5-year survival relative rate for people with anal cancer was 70.1%. The SEER data groups cancer statistics into localized, regional, and distant stages as follows:

Anal and colon cancer both impact your lower digestive system and can affect your bowel function.

Treatment and survival rates for both of these cancer types are similar, but the causes are very different. Talk with a doctor about regular screening if you have an increased risk of either condition.