How Do You Detect Colorectal Cancer? 6 Screening Tests

Learn about screening tests, diagnosis, staging, and treatment for colorectal cancer

Colonoscopy is the best way to detect colorectal cancer. If you are 45 years old or older or if colorectal cancer runs in your family, it is recommended to talk to your doctor about colorectal cancer screening.

6 types of colorectal cancer screening tests

1. Virtual colonoscopy or computed tomography (CT) colonography: Creates a series of images of the colon and rectum from outside the body using X-ray equipment.
2. Sigmoidoscopy: Inspects the rectum and lower (sigmoid) colon with a sigmoidoscope, a flexible lighted tube with a viewing lens and a tool for tissue removal.
3. Standard (or optical) colonoscopy: Uses a flexible lighted tube with a viewing lens and a tool for tissue removal, to inspect the rectum and entire colon.
4. Double-contrast barium enema: Involves administering a barium enema and obtaining X-ray images after the barium has migrated into the colon; not ideal to detect precancerous polyps, but an option if a colonoscopy or other suitable test is not available.
5. Fecal occult (hidden) blood tests (FOBT): Done to detect blood in stools. If blood is found, a colonoscopy is usually the next step to see if the source of the blood is from within the colon:
   1. Fecal immunochemical test (FIT): Looks for concealed blood in the stool by detecting the human hemoglobin contained in red blood cells.
   2. Guaiac-based fecal occult blood test (gFOBT): Similar to FIT but employs a different type of chemical reaction to detect the presence of blood in the stool
6. Stool DNA test: Detects trace quantities of blood in the stool (through an immunochemical test similar to FIT), as well as nine DNA biomarkers in three genes linked to colorectal cancer and precancerous advanced adenomas.

How is colorectal diagnosed?

Further testing is often required before colon or rectal cancer can be diagnosed. When any test other than a colonoscopy indicates abnormalities, a doctor may order a colonoscopy to view the colon in its entirety. Tests may include:

• Blood tests
• Endorectal ultrasound
• Positron emission tomography (PET) and computed tomography (CT) scan
• Magnetic resonance imaging
• CT scan
• Chest X-ray

Other tests used to confirm a diagnosis of colorectal cancer may include:

• Surgery: Procedure to remove the tumor and see how far it has spread through the colon.
• Lymph node biopsy: Removal of all or part of a lymph node; tissue is checked for cancer cells. This may be done during surgery or by endoscopic ultrasound-guided fine-needle aspiration biopsy.
• Carcinoembryonic antigen (CEA) assay: Measures the level of CEA in the blood. CEA is released into the bloodstream from both cancer cells and normal cells. When found in higher-than-normal amounts, it can be a sign of colon cancer or other conditions.

What are screening recommendations for colorectal cancer?

The American Society of Clinical Oncology has developed guidelines for patients who are at average risk, have no family history of colorectal cancer, and are relatively healthy.

Beginning at the age of 45, both men and women should begin screening for colorectal cancer. If you have risk factors, you should begin screening for colorectal cancer earlier.

Consult your doctor if you believe you could be in the high-risk category. Prevention is critical, especially for people who are at higher risk.

What are risk factors for developing colon cancer?
See Answer

What are risk factors for colorectal cancer?

The exact cause of colorectal cancer is unknown, although genetic mutations may play a role. Most people have about a 5% chance of getting colorectal cancer. However, people with the following risk factors may have a higher likelihood of developing the condition:

• Older than 50 
• Male sex
• Family history of colorectal cancer
• History of polyps or growths
• History of bowel-related diseases
• Smoking
• Obesity or overweight
• Inflammatory conditions of the bowel, such as ulcerative colitis and Crohn’s disease
• Poor nutrition (diet heavy in red and processed meats)
• Type II diabetes
• Sedentary lifestyle
• Being African American
• History of other cancers, including uterine and ovarian cancer
• Genetic disorders, such as familial adenomatous polyposis, Gardner syndrome, hereditary nonpolyposis colorectal cancer (Lynch syndrome), and Peutz-Jeghers syndrome

What are different types of colorectal cancer?

Colorectal cancers often grow slowly over several years. A noncancerous polyp on the inner lining of the colon or rectum often precedes the formation of a tumor. Not all polyps develop into cancer, however.

There are five types of colon and rectal cancers:

• Adenocarcinoma: Tumors form in the cells that produce mucus. Early tumors in colorectal cancer begin as tiny polyps that can expand and become malignant tumors.
• Gastrointestinal stromal tumors (GIST): These begin in cells in the colon wall called interstitial cells of Cajal. These tumors can form anywhere in the digestive tract but are most often detected in the colon.
• Lymphoma: This type of cancer usually begins in a lymph node, which is part of the immune system. It can also start in the colon, rectum, or other organs.
• Carcinoid tumors: Tumors form in the hormone-producing cells of the intestine.
• Sarcoma: Tumor starts in blood vessels, muscles, or connective tissue in the colon and rectum wall.

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What are signs and symptoms of colorectal cancer?

About 80% of patients diagnosed with colon cancer have no symptoms. Symptoms usually do not usually present until the cancer has advanced, making regular screening essential. 

Symptoms of colorectal cancer may include:

• Abdominal pain, tenderness, or cramps
• Bloody stools (bright red or very dark)
• Narrow stools
• Diarrhea
• Constipation
• Unexplained anemia
• Unexplained weight loss
• Abdominal bloating
• Loss of appetite
• Vomiting
• Fatigue

Since colorectal cancer symptoms are very similar to those of other gastrointestinal diseases, proper diagnosis is critical.

What are the stages of colorectal cancer?

Stage 0 (carcinoma in situ)

• Abnormal cells are observed in the mucosa (innermost layer) of the colon wall.
• These cells may develop into cancer and spread to surrounding normal tissue.

Stage I

• Cancer begins in the mucosa (innermost layer) of the colon wall and spreads to the submucosa (tissue layer adjacent to the mucosa) or the muscle layer of the colon wall.

Stage II

• Stage IIA: Cancer has migrated from the muscular layer to the serosa (outermost layer) of the colon wall.
• Stage IIB: Cancer has progressed from the colon wall's serosa (outermost layer) to the tissue that lines the organs in the abdomen (visceral peritoneum).
• Stage IIC: Cancer has spread to adjacent organs through the serosa (outermost layer) of the colon wall.

Stage III

• Stage IIIA (any one or combination of the following)
  • Cancer has progressed through the colon wall's mucosa (innermost layer) to the submucosa (tissue layer adjacent to the mucosa) or the muscle layer.
  • Cancer has progressed to 1-3 surrounding lymph nodes.
  • Cancer cells have grown in tissue near the lymph nodes or through the mucosa (innermost layer) of the colon wall to the submucosa (layer of tissue next to the mucosa).
  • Cancer has spread to 4-6 neighboring lymph nodes.
• Stage IIIB (any one or combination of the following)
  • Cancer has spread through the colon wall's muscular layer to the serosa (outermost layer) or has spread through the serosa to the tissue that borders the organs in the abdomen (visceral peritoneum).
  • Cancer has progressed to 1-3 surrounding lymph nodes, or cancer cells have grown in the tissue around the lymph nodes, as well as the muscle layer and serosa (outermost layer) of the colon wall.
  • Cancer has progressed to 4-6 surrounding lymph nodes, through the mucosa (innermost layer) of the colon wall to the submucosa (tissue layer next to the mucosa) or the colon wall's muscle layer.
  • Cancer has spread to at least 7 neighboring lymph nodes.
• Stage IIIC (any one or combination of the following)
  • Cancer has spread through the colon wall's serosa (outermost layer) to the tissue that lines the organs in the abdomen (visceral peritoneum).
  • Cancer has progressed to 4-6 surrounding lymph nodes, through the muscular layer of the colon wall to the serosa (outermost layer), or through the serosa to the tissue that borders the organs in the abdomen (visceral peritoneum).
  • Cancer has progressed to 7 or more neighboring lymph nodes or through the colon wall's serosa (outermost layer) to surrounding organs.
  • Cancer cells have grown in the tissue around the lymph nodes or has spread to one or more neighboring lymph nodes.

Stage IV

• Stage IVA: Cancer has progressed to a site or organ other than the colon, such as the liver, lung, ovary, or a distant lymph node.
• Stage IVB: Cancer has progressed to other areas or organs other than the colon, such as the liver, lung, ovary, or a distant lymph node.
• Stage IVC: Cancer has progressed to the tissue lining the abdominal wall and may have migrated to other places or organs.

How is colorectal cancer treated?

Treatment options vary depending on age, stage of cancer, and overall health condition. Patients may receive one treatment or a combination of treatments.

Surgery

Surgery is the most common treatment for colon cancer at all stages. Surgical options may include:

• Local excision
  • If cancer is discovered at an early stage, the doctor may be able to remove it without having to cut through the abdominal wall.
  • Instead, the doctor may insert a tube with a cutting instrument into the colon and remove the tumor. This is called a local excision.
  • If cancer is discovered in a polyp stage, the doctor may recommend polypectomy.
• Resection of the colon with anastomosis
  • If the cancer is more advanced, the doctor may do a partial colectomy (removing cancer and a small amount of healthy tissue around it).
  • An anastomosis may then be performed (sewing the healthy parts of the colon together).
  • In addition, the doctor will often remove lymph nodes surrounding the colon and analyze them under a microscope to check whether they have cancer.
• Resection of the colon with colostomy
  • If the doctor is unable to suture the two ends of the colon back together, a stoma (a hole on the outside of the body) is created to allow waste to flow through.
  • To collect waste, a bag is wrapped around the stoma.
  • Sometimes the colostomy is only required until the lower colon heals, after which it can be reversed.
  • However, if the doctor decides to remove the whole lower intestine, the colostomy may be permanent.

After the doctor removes all visible cancer during surgery, some patients may be administered chemo or radiation therapy to destroy any remaining cancer cells. 

Radiofrequency ablation

This treatment uses a probe with small electrodes to destroy cancer cells. Sometimes, the probe is put straight through the skin, requiring just a local anesthetic. In other cases, the probe is introduced through an abdominal incision. This is performed in a hospital under general anesthesia.

Cryosurgery or cryotherapy

Cryosurgery is a procedure that involves freezing and destroying cancerous tissue using a specific instrument.

Chemotherapy

Chemotherapy uses medications that are meant to slow the growth of cancer cells, either by killing them or preventing them from growing. Chemotherapy medications are administered orally, intravenously, or intramuscularly (systemic chemotherapy).

Chemotherapy medications primarily target cancer cells in the cerebrospinal fluid, an organ, or a bodily cavity, such as the abdomen when administered directly into those locations (regional chemotherapy).

Chemoembolization of the hepatic artery

Cancer that has progressed to the liver may be treated with this method. The hepatic artery (primary artery that delivers blood to the liver) is blocked, and anticancer medications are injected between the obstruction and the liver. Depending on what is used to restrict the artery, the blockage could be temporary or permanent. The portal vein, which delivers blood from the stomach and intestine, continues to supply blood to the liver.

Radiation therapy

Radiation therapy uses high-energy X-rays or other forms of radiation to either kill or prevent cancer cells from developing. Radiation treatment is classified into two types:

• External radiation therapy uses a machine located outside the body to direct radiation toward the cancerous location.
• Internal radiation therapy uses a radioactive chemical that is sealed in needles, seeds, wires, or catheters that are inserted into or near the malignancy.

Targeted therapy

Targeted therapy uses medications or other substances to locate and destroy cancer cells. Targeted treatments are less likely to kill normal cells than chemotherapy or radiation therapy.

Immunotherapy or biologics

This treatment uses the patient's immune system to combat the disease. Substances produced by the body or created in a laboratory are used to augment, enhance, or restore the body's natural anticancer defenses.

Clinical trials

Clinical trials are being conducted to explore new forms of treatment for colorectal cancer to determine whether novel cancer therapies are safe and effective or if they are better than the usual treatment. Many of today's mainstream cancer therapies are based on prior clinical studies.

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What are survival rates for colorectal cancer?

The 5-year survival rates for colorectal cancer vary depending on the stage:

• Localized colon cancer diagnosed at an early stage: 90%
• Advanced colon cancer that has spread to nearby organs: 71%
• Colon cancer that has spread distantly through the body: 13%

However, these survival rates are merely estimates and may not reflect advancements in diagnosis and treatment in recent years.