Anal cancer vs. rectal cancer: Differences explained

Share on Pinterest

Anal cancer is relatively rare. Most people have about a 1 in 500 risk of developing anal cancer in their lifetime. However, colorectal cancer, which includes statistics for rectal cancer, is much more common, with a 1 in 26 risk for females at birth and 1 in 23 for males.

Location

Anal cancer and rectal cancer are both malignancies that develop in different parts of the lower digestive tract.

Anal cancer develops in the anal canal. This is a tube about 1 to 1.5 inches long at the end of the rectum where the body expels stool. Rectal cancer develops in the rectum, which sits above the anal canal. It is the last portion of the digestive tract.

The types of tissue lining the rectum and anus are also different.

Bowel anatomy

The anus and rectum are both at the end of a long tube that carries waste products from the small intestine to the outside of the body. While the anal canal is short, the colon is about 5 feet long.

Doctors classify the bowels into five different sections:

• The cecum is the opening to the colon that connects the part of the small intestine to the beginning of the large intestine.
• The ascending colon follows, sitting along the right side of the abdomen.
• The transverse colon crosses the body from right to left.
• The descending colon continues down the left side of the body.
• The sigmoid colon, which is “S” shaped, joins the colon to the rectum, which then eventually connects to the anal canal.

Causes

While doctors and researchers do not know what causes anal cancer and rectal cancer, there are risk factors that can increase the likelihood that people will develop these cancers.

For rectal cancer, risk factors include:

• a family history of colon or rectal cancer in a parent, sibling, or child
• a personal history of colon, rectal, or ovarian cancer
• having high risk colon polyps
• a diagnosis of ulcerative colitis or Crohn’s disease for 8 or more years
• smoking
• excessive alcohol consumption
• older age
• obesity

Compared with rectal cancer, family history does not play such an important role in anal cancer. Risk factors for anal cancer include:

• past infection with human papillomavirus (HPV)
• anal warts
• personal history of cancer of the cervix, vagina, or vulva
• having multiple sexual partners
• participating in receptive anal sex
• smoking
• being immunocompromised

Both anal and rectal cancer can have similar symptoms. However, people might notice some differences depending on the location and size of the cancer.

Diagnosis of anal cancer and rectal cancer involves many of the same tests and procedures. For rectal and anal cancer, doctors might perform the following tests and procedures:

• Digital rectal exam: This is a procedure in which a doctor inserts a gloved finger into the rectum to feel for any lumps.
• Proctoscopy: This involves a thin tube that allows doctors to examine the rectum and anus.
• Endoanal or endorectal ultrasound: This is a procedure that involves an ultrasound probe to provide a picture of the rectum using high energy sound waves.
• Colonoscopy: This is a procedure that uses a scope to view inside the anal canal, rectum, and colon for polyps or other lumps.
• Biopsy: A biopsy removes tissue cells in order to test them for cancer. A doctor can perform a biopsy during a colonoscopy.

Depending on the results, doctors might also order imaging tests to determine whether the cancer has spread to other parts of the body. These tests may include:

• CT scan
• X-ray
• MRI

Treatment approaches for anal cancer and rectal cancer may vary depending on the stage of the cancer, its size, and its location.

Both anal and rectal cancer treatments can include surgery to remove cancerous cells and some healthy tissue around them. The type of surgical procedure a doctor may recommend depends on many factors. It can range from a local resection, often used for small tumors that have not spread, to a larger surgery involving removing part of the sigmoid colon.

Other treatment options for anal cancer and rectal cancer include:

• Radiation and chemotherapy: These treatments are common to kill cancer cells and stop anal and rectal cancer from growing, but the specific drugs prescribed might vary. Doctors may also prescribe radiation and chemotherapy before surgery to shrink a tumor.
• Immunotherapy: This is a biological treatment prescribed for both anal and rectal cancer. Immunotherapy uses the body’s immune system to fight the cancer.
• Targeted therapy: This treatment includes different monoclonal antibodies to target rectal cancer cells and kill them.

Helping to prevent anal and rectal cancers involves many of the same strategies recommended to help prevent all cancers. These generally involve diet, exercise, and scheduling regular screenings. However, there are some specific prevention considerations for each type.

Overall cancer prevention advice includes:

• Diet and exercise: A diet rich in fruits, vegetables, and whole grains, combined with regular activity, can reduce the risk of all cancers.
• Smoking: Quitting or avoiding smoking reduces a person’s risk of many types of cancer.
• Weight: Maintaining a moderate weight can reduce the risk of rectal cancer and potentially anal cancer.
• Screenings: Colonoscopies can help a doctor detect precancerous changes in the anal canal, rectum, and other parts of the colon. Early detection often leads to better outcomes.

Strategies to help prevent anal cancer include:

• HPV vaccine: Most cases of anal cancer are the result of HPV. Vaccinating against HPV can reduce the risk of developing anal cancer.
• Sexual habits: Using a condom or other barrier method during sexual activity, especially with multiple partners, can reduce a person’s risk of developing HPV.
• Anal pap and other screening: People who are at a higher risk of developing anal cancer can speak with a healthcare professional about scheduling regular anal pap tests to detect early cell changes that can lead to anal cancer. There is no standard timeframe for regular anal pap tests, and a healthcare professional may also recommend other screenings.

Strategies to help prevent rectal cancer involve:

• Removing polyps: Regular screenings help to detect polyps in the rectum that can sometimes develop into cancer. Having a doctor remove these polyps can help prevent cancer.
• Aspirin: Research suggests that taking aspirin might lower the risk of developing colorectal cancer and the risk of dying from it. However, taking aspirin can increase the risk of stroke and intestinal bleeding. It is important to speak with a healthcare professional before taking aspirin regularly.

The outlook for anal cancer and rectal cancer depends on many factors, including the stage at diagnosis, the location of the cancer, and how effective treatment is.

Overall, for both anal and colorectal cancer, the 5-year relative survival rate is 80%, which means people diagnosed with anal cancer are about 80% as likely as people who do not have it to be alive 5 years after their diagnosis. More advanced stages of cancer typically have lower 5-year survival rates.

Experts continue researching new treatments for anal and rectal cancers and new ways to help prevent them.

Anal and rectal cancers are different even though they both occur in the lower digestive tract.

Anal cancer is less common and often has links with HPV. Rectal cancer is more common, with risks including family history, obesity, and certain diseases.

Diagnosing anal cancer and rectal cancer often involves the same tests, and treatment options range from surgery to radiation and chemotherapy.

To help prevent cancer, lifestyle choices are important, as are regular screenings. A person can talk with a healthcare professional about specific risk factors for anal and rectal cancer and prevention strategies to reduce individual risk.