Colon Cancer

Colon cancer is the most common form of GI cancer, making up around 30% of all GI cancer cases. Colorectal cancer (colon and rectal combined and often referred to as “CRC”) is the third most commonly diagnosed cancer among men and women, and the second-leading cause of cancer deaths in the U.S. You can prevent colon cancer by getting screened. The rates of young people being diagnosed are increasing at an alarming rate, they doubled between 1995 to 2019. If caught in its earliest stages, there’s a good chance for survival.  

What is colon cancer?

The colon is part of the large intestine, located between the appendix and the rectum. The colon’s role in the digestive system is to extract water and nutrients from what we eat and drink, and then to form poop. There are several sections to the colon:

Right side: Consists of the cecum, ascending colon, hepatic flexure, and half of the transverse colon.

Left side: Consists of the splenic flexure, other half of the transverse colon, descending colon, sigmoid colon, and rectum.

While many people group them together, colon cancer and rectal cancer are technically two distinct cancers that come with unique treatment approaches.

Types of colon cancer

Almost all colon cancers (up to 98%) are adenocarcinomas. These are cancers that begin in glands that line internal organs and make mucus and other fluids. 

Adenocarcinomas

Most adenocarcinomas in the colon grow from adenomatous polyps (adenomas). Screening for colorectal cancer through a colonoscopy is one way to identify and remove these polyps before they become cancer. Several new technologies—like non-invasive screening tests using stool and blood—are also able to identify if someone has adenomas.

If adenomas are caught and removed, in a pre-cancerous phase or in the earliest stages of becoming cancerous, the disease is very treatable and survival rates are high.

Rare types of colon cancer

A few other very rare types of colon cancer include carcinoid tumors (neuroendocrine), gastrointestinal stromal tumors (GISTs), non-Hodgkin lymphoma, leiomyosarcoma, squamous cell carcinoma, and melanomas. 

Staging colon cancer

If you have colon cancer, you need to know your stage. This helps you understand the size of your tumor, where the cancer is now, and the best treatment plan for your unique situation. 

Colon cancer is staged on a scale from 0-4 (many researchers use roman numerals 0-IV) using the TNM staging system. In general:

• Stage 0 (carcinoma in situ): Abnormal cells are in the inner layer of the colon.
• Stage 1: Cancer is in the submucosa and possibly the muscle layer of the colon.
• Stage 2: Cancer has spread past the muscle layer of the colon but not to lymph nodes.
• Stage 3: Cancer is in at least 1 lymph node.
• Stage 4 (also called “metastatic”): The cancer has spread to distant organs like the liver and/or lungs. It may also be in lymph nodes. 

What causes colon cancer?

Risk factors put you at a higher risk of getting cancer. Some risk factors can be controlled with lifestyle changes, and others cannot. Older age, smoking, and obesity increase your risk of many cancers.

Just because you have a risk factor, that doesn’t mean you will get cancer. 

These are scenarios researchers have found that can increase your risk:

• Colon polyps
• Family history of colorectal or other cancers like endometrial, ovarian, stomach, urinary tract, brain, and pancreatic 
• Personal history of colorectal cancer
• Certain genetic syndromes like familial adenomatous polyposis (FAP) and Lynch syndrome
• Inflammatory bowel disease (IBD): Crohn’s and ulcerative colitis

Preventing colon cancer

Getting screened for colon cancer is the No. 1 way to reduce your risk. Colon cancer is one of the few cancers that can be prevented. There are several FDA-approved screening options:

• Colonoscopy
• Stool-based tests (like FIT and Cologuard)
• Blood-based tests (Shield)
  

It’s important to discuss your screening options with a doctor; each has pros and cons. Not all options are covered by insurance nor are all of them available to patients of every age. 

As with every cancer, there are steps you can take to adopt a healthy lifestyle and reduce your overall cancer risk, such as maintaining a healthy weight, not smoking, and limiting or eliminating alcohol. 

For colorectal cancer specifically, studies have shown that eating a lot of red and processed meats and drinking alcohol increases risk. Many researchers around the world are looking into why there’s been an increase of cancer cases among young adults since the early 1990s, and several are exploring the role of diet and environmental factors.

Learn more about cancer prevention from the American Institute for Cancer Research.

How common is colon cancer? 

Around 1 in 24 men and 1 in 26 women will be diagnosed with colorectal cancer; and 1 out of 5 new cases is someone under age 55. 

The 2025 American Cancer Society estimated rates for colon cancer in the United States:

About 107,320 new cases of colon cancer (54,510 in men and 52,810 in women).

The average age of diagnosis is 66 years old. It is slightly more common in men compared to women.  

It’s especially concerning for young adults: Early onset cases (under age 50) are expected to increase by more than 140% by 2030, and colorectal cancer is now the No. 1 cause of cancer deaths in men and the No. 2 cause in women under age 50.

See more statistics from the National Cancer Institute’s SEER program. 

What are my odds of surviving it?

Colon cancer is highly treatable if caught early. Doctors use what’s called “survival statistics” to understand the likelihood of a patient beating the disease.

According to the National Cancer Institute, 65% of patients are alive five years after a colorectal cancer diagnosis.

Detailed survival statistics are based on where the cancer is located and if it has spread:

Localized

The cancer hasn’t spread

• 34% of cases
• 91.5% of patients are alive five years after diagnosis

Regional

The cancer spread to nearby lymph nodes

• 37% of cases
• 74.6% of patients are alive five years after diagnosis

Distant

The cancer has spread to lymph nodes and/or organs

• 23% of cases
• 16.2% of patients are alive five years after diagnosis
  

What types of tests should I expect to undergo?

Doctors typically use these tests to diagnose colon cancer:

• Colonoscopy
• Blood tests
• Biopsy
  

Once you’ve been diagnosed, you can expect these tests:

• CT scan
• Chest x-ray
• PET scan
  

Ask your doctor about these additional tests—ideally before you begin treatment.

• Biomarker testing
• Genetic testing
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I’m facing a diagnosis: What are my next steps?

If you’re facing a diagnosis, the GI Cancers Alliance is here for you. 

If you’re newly diagnosed, work with your doctor to create a treatment plan. 

Colon cancer treatment plans may include:

• Surgery 
• Chemotherapy
• Targeted therapy
• Immunotherapy

We strongly encourage you to get a second opinion from another trusted doctor so you feel confident moving forward.