Blood Tests For Colon Cancer: Is It Recommended?

Colon or rectal cancer, aka colorectal cancer, is the third most common cancer type. According to the American Cancer Society, an estimated 106,970 new colon cancer cases are going to be diagnosed in America in 2023.¹

If left untreated, colon cancer can quickly metastasize (spread to other parts of the body) and become incurable. Therefore, it's essential to go for screening so your doctor can detect colon cancer early.

In this post, you'll get an overview of the symptoms and causes of colon cancer, plus answers to frequently asked questions. Can colon cancer be detected in blood work? Let's find out.

What is colon cancer?

Colon cancer is a condition where the damaged or abnormal cells in the colon multiply rapidly. Sometimes, such abnormally growing cells can form polyps. When these polyps remain undetected or untreated, they can develop into a malignant tumor — however, cancer can also form when there are no polyps.

Stages of colon cancer can be determined by the TNM (tumor, nodes, and metastasis) system that analyzes specific information:

• Tumor: what is the size of the tumor, and how far has it grown within the rectum or colon?

• Nodes: what is the degree of spreading to nearby lymph nodes?

• Metastasis: has the cancer spread to other areas of the body?

Based on the TNM information gathered, we can classify the progress of colon cancer through five stages:

• Stage 0 (in situ): cancer is still in its early stages, and lesions form on the inside most layer of the colon 

• Stage I: cancer moves into the next tissue layer of the colon

• Stage II: cancer spreads to the outermost layer of the colon

• Stage III: cancer spreads into the lymph nodes surrounding the colon

• Stage IV: cancer metastasizes beyond the colon to distant parts of the body

Signs & symptoms of colon cancer

It can be tricky to notice early signs of colon cancer. The symptoms of colon cancer often appear as the disease progresses. After a while, some of the symptoms you may begin to experience or signs you may see include the following:

• Spots of blood in your stool

• Changes in bowel movements (e.g., constipation, diarrhea)

• Change in bowel habits (e.g., loose/thin stools)

• Abdominal pain

• Stools may look dark brown or black if there’s blood in them

• Abnormal weight loss

• Needing to go to the bathroom repeatedly despite having just done so

• Weakness and fatigue

Still, these symptoms may vary from person to person depending on the size and location of the cancer in your large intestine.

Types of colon cancer

Most colon cancers are adenocarcinomas. This is a type of cancer that affects glands that line body organs, including the colon. In fact, 96% of colorectal cancers are adenocarcinomas that are derived from epithelial cells.²

Other types of cancers (particularly colorectal cancers) include:

• Lymphoma. This type of cancer affects the immune system cells and usually starts in lymph nodes, but it can also be found in the rectum or colon.

• Sarcomas. This is a rare type of cancer that affects blood vessels, muscles, or connective tissue, such as those in the colon or rectum. 

• Carcinoid tumors. These start from hormone cells found in the intestines.

• Gastrointestinal stromal tumors (GISTs). These are tumors that start from a special type of cells in the intestines called the interstitial cells of Cajal.

Colon cancer can also spread to the colon from somewhere else in the body. One of the common types of cancer that metastasizes to the colon is melanoma, alongside breast cancer. Less than 2% of colon cancers are the result of melanoma, but when it occurs, it can be far more aggressive and difficult to treat. It's also hard to diagnose since it's so rare.

Causes of colon cancer

Colorectal cancer is the complex interaction of genetic and environmental factors. There are numerous changes in the cells’ genetic picture, such as inactivation of tumor-suppressor and DNA repair genes, as well as simultaneous activation of oncogenes, leading to growth advantage to the cells and, ultimately, loss of growth control and cell cycle. 

Typically, no two cancers are perfectly alike, and each person’s cancer may have a different genetic makeup and cause.

Medical conditions that increase colon cancer risk

You're at more risk of getting colon cancer if you have any of the following conditions:

• Inflammatory intestinal diseases such as ulcerative colitis, Crohn's disease, or any other inflammatory bowel disease

• Hereditary CRC syndromes like Lynch syndrome or familial adenomatous polyposis 

• Cancer and polyp history if you or a family member has been diagnosed with CRC or polyps

Lifestyle factors that increase the risk of colon cancer

You may be at greater risk of colon cancer if you fall into any one of these lifestyle categories:

• People with obesity. High weight increases the risk of colon cancer.

• People who smoke. Using tobacco products puts you at higher risk of colon cancer.

• People with high alcohol intake. Alcohol is an established risk factor of colon cancer for those who are heavy drinkers (more than three drinks per day). 

• Low physical activity. There’s an inverse relationship between physical activity and colon cancer but not rectal cancer.

Diagnosing colon cancer

Colonoscopy and stool tests like fecal immunochemical tests and fecal occult blood tests are common colon cancer screening tests. A colonoscopy involves using a long tube with a video camera to view any suspicious areas inside the colon as well as remove polyps and take samples as needed. 

If your doctor suspects the presence of colon cancer, they may do a biopsy. This involves obtaining a tissue sample of the suspicious area of the colon through the scope for further lab tests.

On the other hand, stool tests are non-invasive. Occult blood is blood in your stool that isn't visible to the naked eye. It can be tested for, and its presence can indicate cancer. Still, scientists have been researching whether blood tests can potentially diagnose colon cancer, raising the question. 

Can blood work detect colon cancer? The US Preventive Services Task Force (USPSTF) suggests a specific blood test for colon cancer detection with major caveats, namely as an aid for CRC detection in average-risk patients that refuse screening by other methods. Furthermore, this blood test is considered inadequate for screening and typically detects more advanced cancer rather than precancerous or in situ lesions that other methods can detect.³

Blood tests for colon cancer

While considered insufficient for screening, blood tests can help monitor the disease progression after diagnosis. These tests include:

• Complete blood count (CBC) test. The CBC blood test measures the cell types in your blood to diagnose if you have anemia. People with colon cancer often develop anemia.

• Liver enzyme test. This blood test determines liver enzyme activity and function and can be abnormal if the cancer has spread to the liver. 

Other tests for colon cancer

Apart from colonoscopy, stool tests, and blood tests, your doctor might suggest doing additional lab tests for colon cancer. These include:

• CT scan. Computed tomography scan involves taking cross-sectional images of your body to help determine colorectal cancer spread.

• Ultrasound. This involves using sound waves to create images of internal organs. The major types include abdominal (moving a transducer along the skin) and endorectal (inserting a transducer through the rectum).

• MRI. This scan uses strong magnets and radio waves to get detailed images of the colon.

Treatment options for colon cancer

There is no "one" treatment for colon cancer. Your doctor may recommend several treatments depending on the cancer type and stage. Your age and overall health might also factor in. The different treatments for colon cancer you receive may include:

• Surgery chemotherapy (chemical medication to kill the abnormal cells)

• Radiation therapy (gamma rays to kill cancerous cells)

• Targeted therapy (antibodies or other drugs that can target specific tissues, genes, and proteins that underpin the cancer cells)

Tips for preventing colon cancer

You cannot prevent colon cancer completely. You can only reduce the chances of getting the condition by:

• Avoiding tobacco products

• Drinking in moderation

• Eating a healthy diet

• Exercising or being physically active

• Maintaining a balanced body mass index (BMI)

• Going for screening starting at age 45⁴

The lowdown

Can colon cancer be detected in blood work? Not as part of screening. While treatments help, you can lower the risk of you and your loved ones getting colon cancer by living a healthy lifestyle and avoiding drugs. Also, remember to go for regular screenings.

Frequently asked questions

What is metastatic cancer?

It refers to cancer spreading from its origin to distant body parts.

What are the most common sites for colon cancer to metastasize?

Colon cancer often spreads to the liver and lungs. Other body parts where cancer may spread include the regional lymph nodes and the peritoneum.

What are the symptoms of bone metastasis?

Common signs and symptoms of bone metastasis include broken bones, bone pain, and limb weakness.