Anal Cancer vs. colorectal cancer: what’s the difference?

Anal cancer and colorectal cancer both develop in the lower gastrointestinal tract, but these types of cancer differ in many ways.

We spoke with gastrointestinal radiation oncologist Emma Holliday, MD, to learn more about the differences between anal cancer and colorectal cancer.

What Parts of the Lower Digestive System Affect Anal Cancer and Colorectal Cancer?

Anal cancer affects the anal canal and anus.

Colorectal cancer affects the colon, including the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.

What are the risk factors for anal cancer and colorectal cancer?

The most common cause of anal cancer is the human papillomavirus (HPV), specifically types 16 and 18, which cause 90% of anal cancers and precancers.

Other less common risk factors for anal cancer include:

  • HIV infection
  • smoking
  • a weakened immune system caused by medicines taken for organ transplants, autoimmune diseases, or other conditions

You are at greater risk for colorectal cancer if you:

Other risk factors for colorectal cancer include:

What Are the Symptoms of Anal Cancer and Colorectal Cancer?

There are some overlapping symptoms. Anal cancer and colorectal cancer can both cause:

  • weakness or fatigue
  • unexplained weight loss
  • abdominal or pelvic pain
  • changes in bowel habits, such as:
    • anal or rectal bleeding
    • constipation
    • diarrhea
    • urgent bowel movement
    • difficulty controlling bowel movements

Symptoms specific to anal cancer include:

  • itching or pain around the anus
  • nodules in or around the anus
  • pain in the anus when passing stool

Symptoms specific to colorectal cancer include:

  • stomach ache
  • bloated feeling
  • a feeling that the bowels are not completely emptied

Anal cancer and colon cancer often have symptoms that can be mistaken for other conditions. For example, anal cancer is often misdiagnosed as hemorrhoids. That’s why regular cancer screenings are so important. Be sure to get a colonoscopy or seek a second opinion if your symptoms don’t go away in a few weeks.

How are anal cancer and colorectal cancer diagnosed?

Anal cancer and colorectal cancer can be diagnosed on regular screening colonoscopy exams even before a patient develops symptoms.

If you develop symptoms between screening colonoscopies, a diagnostic colonoscopy may be performed to look inside the anal canal, rectum, and colon to check for cancer. A biopsy can be performed to determine whether or not cancer is present.

How are anal cancer and colorectal cancer treated?

The most common type of cancer cell that causes anal cancer is squamous cell carcinoma. It responds well to and is usually treated with radiation therapy and chemotherapy given together. We can sometimes use a procedure called a local excision to remove very small early stage anal cancers that have not spread to the lymph nodes and are not invading the sphincter. This represents a minority of anal cancer cases.

Treatment options for colorectal cancer differ depending on the location of the cancer. Tumors in the colon may be treated with surgery alone, or chemotherapy may be given before or after surgery, depending on the size of the tumor and whether or not the cancer has spread to the lymph nodes.

Tumors in the rectum are more likely to come back after surgery, so rectal cancer is often treated with chemotherapy and/or radiation before surgery. Patients with rectal cancer have different treatment options depending on the location of the tumor in the rectum, its size, and whether the cancer has spread to the lymph nodes. These treatment options are:

  • chemo followed by surgery and no radiation if the tumor shrinks enough after chemotherapy
  • chemotherapy followed by radiation and no surgery if there is no more cancer after chemotherapy and radiation
  • chemotherapy, radiation and surgery if there is a high risk of recurrence

Getting the right diagnosis is the best way to make sure you get the right treatment. And with early detection, both anal cancer and colorectal cancer can be successfully treated.

Request an appointment online with MD Anderson or by calling 1-877-632-6789.

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