Colon cancer begins in the large intestine, which is the final part of the digestive tract. The functions of the intestine are reabsorbing fluids, processing waste products and eliminating solid waste from the body. Colon cancer is characterized by the development of malignant tumors arising in the inner wall of the colon or rectum. It usually begins as small, noncancerous (benign) clumps of cells called polyps that form on the inside of the colon. Over time these polyps can develop into colon cancers. Colon cancer is called colorectal cancer, when involves both the colon and rectum.
A blood test called tumor markers may be raised in colon cancer. However, it is neither specific nor sensitive for cancer diagnosis. Colon cancer often produces a tumor marker called carcinoembryonic antigen or CEA. However, the test will not detect all colon cancers. The is also done to monitor the progress of treatment.
How is colon cancer diagnosed?
The diagnosis will be made after analyzing the patient’s medical and family history. The doctor will also perform a physical exam and a rectal exam to determine whether lumps or polyps are present. If the signs and symptoms indicate colon cancer, then certain diagnostic tests are recommended to confirm the diagnosis. The tests include
- Colonoscopy and sigmoidoscopy use a scope to examine the inside of the colon. A colonoscopy may also be advised to be performed regularly to screen high-risk and elderly individuals for colon cancer.
- Blood tests, such as carcinoembryonic antigen (CEA) test
- Fecal testing, guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT)
- Computed tomography (CT) scan and magnetic resonance imaging (MRI) scan as needed
What are the types of colon cancer?
Types of colon cancer include
- Adenocarcinoma: Most colorectal cancers are adenocarcinomas. These cancers start in cells that make mucus, which lubricates the inside of the colon and rectum.
- Carcinoid tumors: These start from special hormone-making cells in the intestine.
- Gastrointestinal stromal tumors (GISTs): These are a rare type of cancer that forms in the special cells in the wall of the colon called the interstitial cells of Cajal.
- Lymphomas: These are cancers of immune system cells. They mostly start in lymph nodes, but they can also start in the colon, rectum or other organs.
- Sarcomas: These can start in blood vessels, muscle layers or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.
What causes colon cancer?
Colon cancer begins when healthy cells in the colon develop mutations (changes) in their deoxyribonucleic acid (DNA). When a cell's DNA is mutated, it may become cancerous. The cells continue to divide and multiply unstoppably. With time, the cancer cells can grow to invade and destroy normal tissue nearby. Also, it could travel to other tissues and organs via blood or lymph vessels to deteriorate their functions. Factors that may increase the risk of colon cancer include
- Older age
- African American ethnicity
- Inflammatory intestinal conditions, such as ulcerative colitis and Crohn's disease
- Inherited syndromes that increase colon cancer risk, such as the familial adenomatous polyposis syndrome (FAPS)
- Family history of colon cancer
- Low-fiber, high-fat diet
- Sedentary lifestyle
- Smoking and alcohol
What are the signs and symptoms of colon cancer?
Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they will most likely vary depending on the cancer's size and location in the large intestine. Signs and symptoms of colon cancer include
- A persistent change in bowel habits, including diarrhea, constipation or a change in the consistency of the stool
- Rectal bleeding or blood in the stool
- A persistent abdominal discomfort, such as cramps, gas or pain
- A feeling that bowel has not emptied after passing stools
- Weakness or fatigue
- Unexplained weight loss
How is colon cancer treated?
- Surgery: Surgery to resect the part of the colon affected and rejoin (anastomose) the healthy segments.
- Radiation therapy: Uses high-powered energy to kill cancer cells.
- Chemotherapy: Uses medications to kill cancer cells.
- Immunotherapy: Immunotherapy modulated the body’s immune system to help fight cancer.
- Targeted drug therapy: Targeted drug treatments target specific abnormalities present within cancer cells and block them, causing cancer cells to die.
- Pain management: Advanced cancers and metastasis can cause significant pain for which the doctor would prescribe appropriate painkillers and rehabilitation.
- Emotional support: Support from family and friends and professional counseling help with the emotional stress and depression that may be associated with a chronic disease.
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Cabebe EC. Colorectal Cancer Guidelines. Medscape. https://emedicine.medscape.com/article/2500006-overview