Adenocarcinoma of Colon

Adenocarcinoma is the most common type of colon cancer, starting in the glands that line the inside of your large intestine. While it typically affects older adults, early detection through screening and advances in treatment have improved outcomes for many patients.

Table of contents

• What is adenocarcinoma of colon?
• What causes adenocarcinoma of colon?
• Risk factors
• Symptoms
• How is adenocarcinoma of colon diagnosed?
• Treatment options
• Associated anatomy

What is adenocarcinoma of colon?

Adenocarcinoma of the colon is a type of cancer that starts in the large intestine. When doctors talk about colon cancer, they are usually referring to adenocarcinoma because it is the most common type. Over 95% of colorectal cancers are adenocarcinomas, a type of tumor that begins in the mucus-producing glands of the colon or rectum.^[14]

This cancer develops from certain growths called polyps (masses of cells like a tumor) in the inner lining of your colon.^[1] The colon is the first and longest part of the large intestine, which is the last part of the digestive system.^[3] Even though adenocarcinomas begin growing in the glands that line your organs, they can eventually spread to other parts of your body, including your brain, liver, lymph nodes, and bone.^[2]

What causes adenocarcinoma of colon?

It’s not completely clear what causes adenocarcinoma of the colon, but researchers know that changes in your cells’ DNA can cause cancer. DNA makes up your genes, which give you traits such as how you look. DNA is passed down to you from your parents.^[1]

For colon cancer to form, many different genes need to change or mutate (undergo abnormal changes). There are two main types of gene mutations that affect colon cancer.^[1]

Inherited gene mutations pass from one generation to the next and cause a small number of cases of colorectal cancer. Acquired gene mutations are not related to family genes and happen during a person’s lifetime. Acquired gene mutations cause most cases of colorectal adenocarcinoma.^[1]

Risk factors

Certain conditions make a person more likely to develop adenocarcinoma of the colon. The group of people at highest risk is women who are age 50 years or older. African-Americans have the highest risk among all races in the United States.^[1]

Additional risk factors include:^[1]

• Smoking
• Having type 2 diabetes
• Not getting enough exercise
• Obesity or being overweight
• Drinking too much alcohol
• Inheriting gene mutations
• A diet high in fat and low in fiber
• Family history of colorectal cancer
• Eating too much red meat and processed meats
• Having ulcerative colitis (a disease in the bowels)
• Having colon polyps

It usually takes about 10 to 15 years for a colon polyp to become cancer, and early screening can prevent this.^[1][12]

Symptoms

When colon cancer is in its early stages, you may not have any symptoms. Many people with colon cancer don’t have symptoms at first.^[1][3] It’s important to see your doctor if you do begin to see any of these symptoms that won’t go away:^[1]

• Blood in your stool or bleeding from your rectum
• Changes in your bowel habits such as constipation, diarrhea, or narrow stools
• A full feeling in your bowels even after you’ve had a bowel movement
• Pain in your abdomen
• Unexplained tiredness or weakness
• Losing weight for an unknown reason

It’s important to remember that blood in stool doesn’t always mean you have colon cancer. Other things, from hemorrhoids to eating certain foods, may change your stool’s appearance. But it’s always better to check with a healthcare provider any time you notice blood in or on your stool.^[12]

How is adenocarcinoma of colon diagnosed?

Fortunately, screening tests for colorectal cancer exist. This means if you have high risk factors but might not have symptoms, you can take a test. Doctors recommend regular screening tests to avoid colon polyps developing into cancer.^[1]

If you do have symptoms, or if the screening test shows possible colorectal cancer, you’ll have more tests. These tests help your doctor know if you have colorectal adenocarcinoma:^[1]

• Blood tests – the doctor looks for certain signs related to your liver, kidney, blood count, and other factors for the possibility of colon cancer
• Colonoscopy – a thin tube with a camera on the end is put in the rectum and colon, and the doctor looks for polyps or other unusual areas
• Biopsy – a small piece of tissue from your colon or rectum is removed and tested for cancer at a lab
• Imaging tests – such as x-rays, ultrasound, MRI, and PET/CT scans, which take pictures of your colorectal area looking for any polyps or odd-looking areas

Blood tests can also track the level of a protein called carcinoembryonic antigen (CEA) over time. The results might show whether the cancer is responding to treatment or detect if the cancer comes back after treatment.^[8]

Treatment options

The three main ways to treat colon cancer are surgery, chemotherapy, and radiation therapy. Treatment options depend on how far along the cancer is and patient characteristics.^[1][4]

Surgery

Surgery is the only curative treatment for localized colon cancer. The type of surgery you have depends on how far along the colorectal adenocarcinoma is. Perhaps a polyp is removed during a colonoscopy. A more serious surgery removes part of your colon to get rid of the cancer.^[1]

Surgery potentially provides the only curative option for patients with limited disease that has spread to the liver or lungs.^[15]

Chemotherapy

Adjuvant chemotherapy (treatment given after surgery to reduce the risk of cancer returning) is standard for patients with stage III disease. Its use in stage II disease is controversial, but current guidelines recommend its use in selected patients with risk factors for recurrence.^[15]

Additional treatment options

There are several approved treatment options for colorectal cancer, including targeted therapy (medicines that attack specific parts of cancer cells) and immunotherapy (treatments that help your immune system fight cancer).^[4] At present, the role of radiation therapy is limited to palliative therapy for selected sites where cancer has spread, such as bone or brain.^[15]

Associated anatomy

• Colon (large intestine)
• Rectum