Colon Cancer

Annormal cells that grow out of control in the large intestine (colon) can become colon cancer. The colon is a tube-shaped organ of the digestive system in the abdomen. It begins where the small intestine and large intestine meet and ends at the rectum, the area of the colon nearest the anus. 

For 2023, the American Cancer Society predicted 106,970 new cases of colon cancer in the United States, as well as 52,550 deaths. Colon cancer affects people of all sexes. It is most often diagnosed in people over age 50. Specific genetic syndromes and personal and family histories can increase your risk.

This article will provide an overview of colon cancer and explain what people should know about their risks. 

What Is Colon Cancer?

Most of the colon works to remove water and nutrients from partially digested food. At the end of the colon, the rectum holds waste before it is released from the anus.

Cancer that grows in any part of the colon that is not the rectum is called colon cancer. Rectal cancer is often discussed alongside colon cancer and referred to as colorectal cancer, but the two can differ significantly. This article will discuss just colon cancer. 

Colon Cancer Symptoms

Colon cancer may have no symptoms. When symptoms do occur, common colon cancer symptoms can include changes in your digestive system and bowel habits (frequency, color, shape, consistency of stool) such as:

• Bright red or very dark blood in your stool
• Diarrhea or constipation
• Feeling that you haven’t fully emptied your bowel
• Skinny stools
• Gas pains, bloating, fullness, or abdominal cramps
• Vomiting

You might also experience:

• Losing weight without trying
• Exhaustion
• Anemia (a low number of healthy red blood cells) from blood loss

These symptoms are most often caused by conditions other than colon cancer. Check with a healthcare provider if you have them.

Early Signs of Colon Cancer

Early colon cancer can be challenging to detect. Some early colon cancers do not have any symptoms. 

According to a study, common symptoms reported by people with early colon cancer include:

• Rectal bleeding in 89%
• Change in bowel habits in 58%
• Perianal symptoms (those affecting the anus, rectum, or perineum), for example, anal pain, in 45%
• Abdominal pain in 24%
• Tiredness in 25%

Late-Stage Symptoms

In the study above, people with advanced colon cancer reported these symptoms more than early-stage cancers:

• Change in bowel habits in 87%
• Abdominal pain in 47%
• Weight loss in 28%

Signs of advanced colon cancer that has spread to other organs include:

• An enlarged liver
• Yellow skin or whites of the eyes (jaundice)
• Trouble breathing

What Causes Colon Cancer?

Colon cancer, like all cancers, develops when a cell undergoes changes to its DNA that enable it to keep growing and dividing out of control. If left untreated, the cell grows, splits, and becomes a tumor, extending into other tissues and organs.

Colon cancer typically develops first through a growth inside the colon called a polyp. Some people have many polyps. Having polyps doesn’t always mean you’ll get cancer. Most are not cancerous and not likely to become cancerous. When they do become cancerous, they grow slowly over many years.

Some people can have a higher risk of colon cancer based on their genetics or environmental factors that increase the likelihood that the colon cells will get genetic mutations that can lead to colon cancer.

As colon cancer grows more advanced, it can spread to the liver, lungs, and other organs. This spread might happen early in cancer development. A 2019 study in Nature Genetics journal suggests that colon cancer tumors may spread very early in their development—before they can even be detected by screenings, years before the cancer is diagnosed.

Colon Cancer Risk Factors

Factors that you can't control that may increase your risk of colon cancer include:

• Your age, with risk increasing the older you are
• A family history of colon cancer in a parent, child, or sibling
• A personal history of colorectal or ovarian cancer
• A personal history of large, high-risk adenomas, a type of polyp that is not cancer but can become cancerous
• Having an inflammatory digestive disorder like the inflammatory bowel diseases (IBD) ulcerative colitis or Crohn's disease for eight or more years

In addition, you're at higher risk of developing colon cancer if you have a genetic syndrome that increases cancer risk of certain cancers. Specifically for colon cancer, this includes:

• Lynch syndrome
• Familial adenomatous polyposis (FAP)

Lifestyle choices you can control that may increase your risk of colon cancer include:

• Drinking three or more alcoholic beverages a day
• Smoking cigarettes
• Eating a lot of red or processed meat
• Having obesity

How Is Colon Cancer Diagnosed?

If you’re at risk of colon cancer and have signs or symptoms, a healthcare provider will order tests to determine if you may have cancer. First, they’ll take your personal and health histories and perform a physical exam. They may use their fingers to examine your rectum to feel for lumps or anything unusual.

Next, they may ask you to do a test at home to look for blood in the stool. These fecal occult blood test kits are shipped to your house or given to you by the healthcare provider. You do the test in the privacy of your home. A similar test, called a DNA stool test, can look for genetic changes that indicate cancer. 

They’ll likely also order some blood tests. These include:

• An analysis of the cells in your blood (complete blood count)
• Levels of your liver enzymes
• A test to look for a chemical (tumor marker) that may signal colon cancer, carcinoembryonic antigen (CEA)

More invasive tests, including a colonoscopy, may be needed. During a colonoscopy, a thin tube containing a camera, light, and tools is inserted through the anus to access your colon. Your provider can visualize the inside of your colon and check for growths. They can also remove and biopsy anything that looks odd to test it for cancer.

Additional imaging tests can look for other growths in the body and determine if cancer has spread to your lymph nodes or other organs. These imaging tests may include a computed tomography (CT) scan, ultrasound, magnetic resonance imaging (MRI), chest X-ray, positron-emission tomography (PET) scan, or angiogram.

Stages of Colon Cancer

During diagnosis, your care team gathers information about your cancer to determine its stage. Cancer staging determines the amount of cancer in the body and where it is located. It can help your provider determine your prognosis (outlook).

Stages range from 0 to 4. The higher the number, the more advanced the cancer. Colon cancer typically starts in the innermost layer of the colon wall, called the mucosa. Stages include:

• Stage 0 is often called carcinoma in situ. This is a precancer or cancer-like abnormal cells that haven't yet spread from the mucosa where they started.
• Stage 1 colon cancer has spread from the mucosa to the submucosa (the layer of connective tissue that's beneath the mucus membrane) or muscle of the colon wall. 
• Stage 2 colon cancer has spread to the colon wall (2a), into the lining of the abdomen (2b), or to nearby tissues and organs (2c).
• Stage 3 colon cancers have spread in the colon and have infiltrated the lymphatic system, leaving cancer in nearby lymph nodes. Stage 3a colon cancer has spread to the submucosa or muscle wall and nearby lymph nodes. Stage 3b has spread to the colon wall or abdomen and is present in many lymph nodes. Stage 3c colon cancer has spread to the abdominal tissues or organs and often many lymph nodes.
• Stage 4 colon cancer is also called metastatic cancer. It has spread from the colon and abdomen to distant organs, including the liver, lungs, ovaries, or distant lymph nodes. If the cancer is present in one of these areas, the stage is considered 4a. If the cancer is present in more than one area, it's stage 4b. If it has spread to the abdominal wall and one of these areas, it's 4c.

Colon Cancer Treatment

Treatment for colon cancer varies based on factors like your general health, age, and treatment goals. It also depends on the stage of cancer and its other characteristics.

Surgery and radiation are local treatments that work to treat primary cancer. Chemotherapy and other drugs are systemic treatments that treat cancer cells that may have spread throughout the body. Treatments are often used in tandem (simultaneously) or one after the other (consecutively). 

Surgery

Most people with colon cancer will have surgery. Traditional surgery (colectomy) includes removing cancer, the nearby colon tissue, and lymph nodes. 

Other surgical treatment options include:

• Destroying cancer with radio waves: Radiofrequency ablation sends radio waves to heat and destroys abnormal cells.
• Destroying cancer with cold: Cryosurgery uses a freezing liquid, or an instrument called a cryoprobe, to freeze and destroy abnormal tissue.

Radiation Therapy

Radiation therapy uses high-energy waves to kill cancer cells. It’s often used after surgery to kill cancer that might have been left behind. It may also be used to shrink cancer before surgery.

In colon cancer, radiation can do the following:

• Destroy cancer with a beam from outside the body: This external beam radiation is the more common type used for colon cancer.
• Destroy cancer with radioactive seeds inside the body: Called brachytherapy, this is more commonly used for rectal cancer.

Chemotherapy

Chemotherapy drugs kill fast-growing cells. Cancer cells grow quickly, but so are other cells in your body, like those in your hair follicles and digestive tract. This can lead to uncomfortable side effects.

The chemotherapy drugs go into the blood and attack cells throughout the body. Two or three chemotherapy medications are often given at a time to reduce side effects and improve efficacy. It may also be combined with radiation. 

Chemotherapy is scheduled in rounds: chemotherapy drugs for a couple of weeks and then a break for recovery before the next round.

Other Medications

Some newer medications can target and kill cancer cells throughout the body, often with fewer side effects than chemotherapy. Their use depends on specific characteristics of your body and cancer and include:

• Targeted therapy drugs attack cancer cells and cause less harm to normal cells. Some that may be used are Avastin (bevacizumab), Erbitux (cetuximab), Vectibix (panitumumab), Zaltrap (ziv-aflibercept), Cyramza (ramucirumab), Stivarga (regorafenib), and Fruzaqla (fruquintinib).
• Immunotherapy drugs help your immune system fight cancer. They include Keytruda (pembrolizumab), Opdivo (nivolumab), and others.

Is Colon Cancer Curable?

If cancer is caught early while still only in the colon, it can be highly treatable and even curable with surgery and other treatments. About half of the people with early colon cancer can be cured with surgery. Because cells can spread without being detected, these cancers often come back.

How to Prevent or Reduce Your Risk of Colon Cancer

There is no way to prevent colon cancer completely. However, you can reduce your risk by eating a healthy diet, keeping a healthy weight, and avoiding smoking tobacco. Reducing alcohol and red and processed meat can also help reduce your risk.

Otherwise, talk to a healthcare provider about your risk and if you need to be screened for colon cancer. These screenings may be uncomfortable or embarrassing for some, but they’re essential to health and in catching cancer before it spreads. You have options.

Screening for Colon Cancer

The American Cancer Society recommends colon cancer screening starting at age 45 for people at average risk for colon cancer. If you have a higher risk, a healthcare provider may recommend you start earlier. Screening should continue until age 75 or 85, depending on a person’s health and life expectancy.

There are two kinds of tests to look for colon cancer. Newer, noninvasive stool-based tests must be done more frequently but are less invasive. Visual tests, like a colonoscopy, need to be done with a healthcare provider but are only needed every five or 10 years, depending on the test. Talk to a healthcare provider about your options. 

Outlook for Colon Cancer

In the most recent year for which data is available through the National Cancer Institute’s cancer database, 2014, the five-year survival rate for colon cancer is 63.9%. That means almost 64% of people diagnosed with colon cancer are alive five years later.

When looking at how advanced the cancer was when it was first diagnosed, the relative survival rate at five years is:

• 91% for localized cancer that is only found in the colon
• 71.4% of regional cancers have spread to nearby tissues and potential lymph nodes
• 14.7% for distant cancers that have spread to other organs in the body

These statistics do not represent individual cases. Factors that can affect a person’s prognosis include their age, general health, and any genetic factors that may have increased their risk of cancer.

Summary

Colon cancer is a type of cancer that starts in the large intestine. It affects people of all sexes, and it's usually diagnosed in those over age 50. 

Colon cancer develops when cells in the colon grow out of control. These cells become a tumor. Polyps are small growths inside the colon. They can be a precursor to colon cancer, but not all polyps become cancerous.

The most common symptoms of colon cancer are changes in bowel habits, blood in the stool, abdominal cramps, gas pains, bloating, unintended weight loss, exhaustion, and vomiting. 

A healthcare provider can find colon cancer early through screening tests. These tests can find cancers that are not yet causing symptoms but can grow and spread. 

Factors that may increase the risk of colon cancer include age, a family history of colon cancer, a personal history of colorectal or ovarian cancer, large or high-risk adenomas, or a digestive disorder. 

Treatment for colon cancer often requires surgery. It can also involve radiation, chemotherapy, targeted therapy, and immunotherapy. 

The outlook for people with colon cancer is good if a healthcare provider finds the cancer early. If it has already spread to the lymph nodes or other body parts, the survival rate drops.