Colorectal Adenocarcinoma

Colorectal adenocarcinoma is the most common type of cancer that develops in the large intestine, affecting the colon and rectum. While it often begins without noticeable signs, regular screening and early detection can significantly improve treatment outcomes and survival rates.

Table of contents

• What Is Colorectal Adenocarcinoma?
• Associated Anatomy
• Causes and Development
• Risk Factors
• Symptoms
• Diagnosis
• Treatment Options

What Is Colorectal Adenocarcinoma?

Colorectal adenocarcinoma is a type of cancer that starts in the large intestine^[1]. The term “colorectal” refers to your colon and rectum, which together make up the large intestine. When doctors talk about colon cancer, they are usually talking about colorectal adenocarcinoma, because it is the most common form of this disease^[1].

The large intestine is made up of the colon, rectum, and anal canal. The colon itself can be divided into different sections: the right colon (which includes the cecum, ascending colon, and right two-thirds of the transverse colon) and the left colon (which includes the left one-third of the transverse colon, descending colon, and sigmoid colon)^[5]. The right colon mainly absorbs water and some nutrients, while the left colon primarily stores and helps eliminate waste from the body^[5].

Colorectal cancer is the third most common cancer diagnosed worldwide and the second most common cause of cancer-related deaths^[5][9]. In 2020, more than 1.9 million new cases and more than 930,000 deaths due to colorectal cancer were estimated to have occurred globally^[9].

• Colon (large intestine)
• Rectum
• Cecum
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon

Associated Anatomy

The colon is part of your body’s digestive system, which breaks down food for your body to use^[3]. The digestive system is made up of the esophagus, stomach, and the small and large intestines. The colon, also called the large bowel, is the main part of the large intestine and is about 5 feet long^[8].

Your colon wall is made of layers of mucous membrane (the innermost lining), tissue, and muscle. Colon cancer starts in your mucosa, which is the innermost lining of your colon^[4]. This layer consists of cells that make and release mucus and other fluids. If these cells change or mutate (undergo abnormal changes in their genetic material), they may create a colon polyp^[4].

Causes and Development

It’s not entirely clear what causes colorectal adenocarcinoma, but researchers understand that changes, called mutations, in your cells’ DNA can lead to cancer^[1]. DNA makes up your genes, and genes give you traits such as how you look. DNA is passed down to you from your parents^[1].

Colorectal adenocarcinoma usually begins as small clumps of cells called polyps that form inside the colon^[3]. Polyps are growths in the inner lining of your colon^[4]. These growths generally aren’t cancerous, but some can turn into colon cancers over time. It usually takes about 10 years for a colon polyp to become cancer^[4][6].

For colon cancer to form, many different genes need to mutate. There are two main types of gene mutations that affect colon cancer development^[1]:

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

Over time, if left undetected or untreated, the cancer works its way through a layer of tissue, muscle, and the outer layer of your colon. The colon cancer may also spread to other parts of your body through your lymph nodes or your blood vessels^[4].

Risk Factors

Certain conditions make a person more likely to develop colorectal adenocarcinoma. A risk factor is anything that increases the chance of getting a disease^[8]. Some risk factors, like smoking, can be changed, but risk factors also include things you cannot change, like your genetics, getting older, and your family history^[8].

Colorectal cancer typically affects older adults, though it can happen at any age^[3]. Most cases occur in people aged 50 and above^[9]. The group at highest risk includes women who are age 50 years or older, and African-Americans have the highest risk among all races in the United States^[1].

Additional risk factors include^[1][8]:

• Having a first-degree relative (parent, sibling, or child) with a history of colon or rectal cancer
• Having a personal history of colon, rectal, or ovarian cancer
• Having a personal history of high-risk adenomas (colorectal polyps that are 1 centimeter or larger in size or that have cells that look abnormal under a microscope)
• Having inherited changes in certain genes that increase the risk of familial adenomatous polyposis (FAP) or Lynch syndrome (hereditary nonpolyposis colorectal cancer)
• Having a personal history of chronic ulcerative colitis (a disease causing inflammation in the bowels) or Crohn disease for 8 years or more
• Smoking
• Having type 2 diabetes
• Not getting enough exercise
• Obesity or being overweight
• Drinking too much alcohol (having three or more alcoholic drinks per day)
• A diet high in fat and low in fiber
• Eating too much red meat and processed meats

Having one or more of these risk factors does not mean that you will get colorectal cancer. Many people with risk factors never develop colorectal cancer, while others with no known risk factors do^[8].

Symptoms

When colon cancer is in its early stages, you may not have any symptoms^[1][4]. Colorectal cancer may not cause any symptoms, especially in its early stages, and some symptoms might be due to other causes like hemorrhoids, diarrhea, infection, or irritable bowel syndrome^[7]. This is why polyps often don’t cause symptoms, making regular screening tests important for finding them before they turn into cancer^[3].

It’s important to see your doctor if you begin to notice any of these symptoms that won’t go away^[1][4][7]:

• Blood on or in your stool (poop): Blood in the toilet after you poop or after wiping, or poop that looks dark or bright red. The blood can be bright red, or the stool may be black and tarry or brick red. It’s important to remember blood in poop doesn’t always mean you have colon cancer—other things like hemorrhoids or eating certain foods can change your stool’s appearance, but it’s always better to check with a healthcare provider
• Persistent changes in your bowel habits: Intermittent or constant diarrhea and/or constipation, a change in the consistency of your stool, or stools that are more narrow than usual, or feeling as if you still need to poop after going to the bathroom
• Abdominal (belly) pain: Belly pain with no known cause, that doesn’t go away or hurts a lot
• Bloated stomach: A full feeling in your bowels even after you’ve had a bowel movement, or bloating that lasts for more than a week or gets worse
• Unexplained tiredness or weakness
• Losing weight for an unknown reason

Diagnosis

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^[1]. Doctors recommend regular screening tests to avoid colon polyps developing into cancer. It takes 10 to 15 years for a colon polyp to become cancer, and early screening can prevent this^[1].

Healthcare providers have screening tests that detect precancerous polyps (growths that might become cancer) before they can become cancerous tumors^[4]. Finding and removing polyps helps prevent colon cancer^[3]. If you are 45 years old or older, talk to your doctor about screening^[6][8].

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][10]:

• Blood tests — the doctor looks for certain signs related to your liver, kidney, blood count, and other factors for the possibility of colon cancer. Blood tests can also track the level of a protein called carcinoembryonic antigen (CEA), which some colon cancers make. The results might show whether the cancer is responding to treatment
• 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. A doctor may pass surgical tools through the tube to take tissue samples and remove polyps
• Biopsy — a small piece of tissue from your colon or rectum is removed and tested for cancer in a lab. Tests can show whether the cells are cancerous and how quickly they’re growing. Other tests can give more information about the cancer cells
• Imaging tests — imaging tests such as x-rays, ultrasound, MRI, and PET/CT scans take pictures of your colorectal area looking for any polyps or odd-looking areas

After colon cancer has been diagnosed, imaging tests are done to find out if cancer cells have spread within the colon or to other parts of the body^[8].

Treatment Options

If colon cancer develops, many treatments can help control it^[3]. The type of treatment you receive depends on how far along the colorectal adenocarcinoma is, the location of the tumor, your general health, and what you prefer or want^[1].

The three main ways to treat colon cancer are^[1][3]:

Surgery: 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 is often the primary treatment for colon cancer.

Chemotherapy: Chemotherapy is a treatment that uses medicines to kill cancer cells or stop them from growing. It is commonly used to treat colorectal cancer and may be given before or after surgery, or when cancer has spread to other parts of the body.

Radiation therapy: Radiation therapy uses high-energy rays to kill cancer cells. It is most often used to treat rectal cancer and may be combined with chemotherapy.

Additional treatment options include^[3]:

• Targeted therapy: These medicines target specific parts of cancer cells to help stop them from growing. Targeted therapy is used for advanced colorectal cancer
• Immunotherapy: Immunotherapy helps strengthen your immune system to fight cancer. Metastatic colorectal cancer is sometimes treated with immunotherapy, particularly for cancers with high microsatellite instability (MSI-H) or DNA mismatch repair deficiency

Thanks to screening tests, early treatment, and new kinds of treatment, fewer people are dying from colon cancer^[4]. Early-stage cancers have higher survival rates than advanced-stage cancers. Timely diagnosis, appropriate treatment, and regular follow-up care are important for improving survival rates and quality of life^[9].