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How Does Colon Cancer Start?

Colon cancer typically starts as a benign polyp, which is an abnormal growth of tissue on the lining of the colon (large intestine). Some polyps are benign (non-cancerous) but may develop into cancer (become malignant).
Colon cancer typically starts as a benign polyp, which is an abnormal growth of tissue on the lining of the colon (large intestine). Some polyps are benign (non-cancerous) but may develop into cancer (become malignant).

Colon cancer is cancer that occurs when cells in the colon (large intestine) start to grow abnormally and out of control.  

Most colon cancers start as benign polyps. Colon polyps are abnormal growths of tissue that project from mucous membranes on the lining of the colon (large intestine). They may be flat or may appear to be attached by a stalk (pedunculated). Some polyps are benign (non-cancerous) but may develop into cancer (become malignant). 

Colon polyps often do not cause symptoms and they are usually detected during a colonoscopy, which is a routine screening test for colon cancer.

Risk factors for developing colon cancer include:

  • Lifestyle-related factors
    • Being overweight or obese 
    • Smoking 
    • Diet 
      • A diet high in red meats (such as beef, pork, lamb, or liver) and processed meats (such as hot dogs and some luncheon meats) 
      • Cooking meats at very high temperatures (frying, broiling, or grilling) 
      • Low blood levels of vitamin D 
      • Alcohol use 
    • Physical inactivity
  • Age over 50 years
  • Personal history of colorectal polyps, colorectal cancer, or inflammatory bowel disease (IBD)
  • Family history of colorectal cancer or adenomatous polyps 
  • Inherited syndromes
    • Familial adenomatous polyposis (FAP) 
      • Attenuated FAP (AFAP)
      • Gardner syndrome 
      • Turcot syndrome 
    • Lynch syndrome (hereditary non-polyposis colon cancer or HNPCC) 
    • Rare inherited syndromes linked to colorectal cancer
  • Racial and ethnic background 
    • African Americans have the highest rates of colorectal cancer in the U.S. 
    • Jews of Eastern European descent (Ashkenazi Jews) have one of the highest colorectal cancer risks in the world
  • Type 2 diabetes 

What Are Symptoms of Colon Cancer?

Symptoms of colon cancer include: 

  • Changes in bowel habits that last for more than a few days
  • Feeling the need to have a bowel movement that's not relieved by having one
  • Blood in the stool
    • Stool may appear dark brown or black
  • Rectal bleeding with bright red blood
  • Abdominal bloating, cramping, or pain
  • Fatigue
  • Weakness
  • Unintended weight loss
  • Low red blood cell counts (anemia) if the colon cancer bleeds into the digestive tract
  • Yellowing skin and eyes (jaundice) if the cancer has spread to the liver
  • Trouble breathing if the cancer has spread to the lungs

How Is Colon Cancer Diagnosed?

Colon cancer is often found during screening tests. Screening for colon cancer is performed with a colonoscopy. The American Cancer Society recommends healthy adults with no risk factors start screening for colorectal cancer at age 45 (the previous recommendation was 50 years).   

Colorectal cancer screening tests include: 

  • Stool-based tests 
    • Less invasive and easier to perform, but need to be done more frequently
    • Any abnormal test result should be followed up with a colonoscopy
      • Fecal immunochemical test (FIT)
      • Guaiac-based fecal occult blood test (gFOBT)
      • Stool DNA test (multitarget stool DNA test [MT-sDNA] or FIT-DNA)
  • Visual (structural) exams

Tests used to diagnose colon cancer include: 

What Is the Treatment for Colon Cancer?

Treatment for colon cancer may involve one or more of the following: 

  • Surgery 
    • Polypectomy and local excision for early-stage colon cancers 
    • Colectomy: surgery to remove all or part of the colon
    • Colostomy or ileostomy
  • Ablation and embolization, used for metastases (spread) of colon cancer to the lungs or liver
    • Radiofrequency ablation (RFA) 
    • Microwave ablation (MWA)
    • Ethanol (alcohol) ablation
    • Cryosurgery (cryotherapy or cryoablation)
    • Arterial embolization (also called trans-arterial embolization or TAE) 
    • Chemoembolization (also called trans-arterial chemoembolization or TACE) 
    • Radioembolization 
  • Chemotherapy 
  • Radiation therapy (more often used to treat rectal cancer but may be used in combination with chemotherapy for colon cancer)
  • Targeted therapy 
    • Drugs that target blood vessel formation (VEGF)
    • Drugs that target cancer cells with epidermal growth factor receptor (EGFR)  changes
    • Drugs that target cells with BRAF gene changes
      • BRAF inhibitors: encorafenib (Braftovi) 
    • Kinase inhibitor
  • Immunotherapy using immune checkpoint inhibitors
    • PD-1 inhibitors
      • Pembrolizumab (Keytruda) 
      • Nivolumab (Opdivo)
    • CTLA-4 inhibitor

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References
https://www.cancer.org/cancer/colon-rectal-cancer.html

https://coloncancercoalition.org/get-educated/what-is-colon-cancer/

https://www.niddk.nih.gov/health-information/diagnostic-tests/colonoscopy