Doctor's Notes on Colon Cancer
Colon cancer is cancer that arises in the lining cells of the large intestine (colon). The exact cause of colon cancer is not completely understood, but most colon cancers are believed to arise from polyps, or small outgrowths in the lining of the colon. Factors that increase a person's risk of developing colon cancer include increasing age, African-American race, high fat intake, a family history of colorectal cancer and polyps, the presence of polyps in the large intestine, and having inflammatory bowel disease.
Signs and symptoms of colon cancer depend on the extent to which the tumor has spread at the time of diagnosis (its stage). Some early cancers may not cause any symptoms. Other colon cancers may cause associated symptoms including blood in the stool, narrow stools, diarrhea or constipation, weight loss, fatigue, and abdominal pain.
Colon Cancer Symptoms
Symptoms of colon cancer may not be present or be minimal and overlooked until it becomes more severe. Cancer screening tests for colon cancer thus are important in individuals 50 and older. Cancer of the colon and rectum can exhibit itself in several ways. If you have any of these symptoms, seek immediate medical help. You may notice bleeding from your rectum or blood mixed with your stool. It usually, but not always, can be detected through a fecal occult (hidden) blood test, in which samples of stool are submitted to a lab for detection of blood.
- People commonly attribute all rectal bleeding to hemorrhoids, thus preventing early diagnosis owing to lack of concern over "bleeding hemorrhoids." New onset of bright red blood in the stool always deserves an evaluation. Blood in the stool may be less evident, and is sometimes invisible, or causes a black or tarry stool.
- Rectal bleeding may be hidden and chronic and may only show up as an iron deficiency anemia.
- It may be associated with fatigue and pale skin due to the anemia.
- Changes in bowel movement frequency
- It usually, but not always, can be detected through a fecal occult (hidden) blood test, in which samples of stool are submitted to a lab for detection of blood.
- If the tumor gets large enough, it may completely or partially block your colon. You may notice the following symptoms of bowel obstruction:
- Abdominal distension: Your belly sticks out more than it did before without weight gain.
- Abdominal pain: This is rare in colon cancer. One cause is tearing (perforation) of the bowel. Leaking of bowel contents into the pelvis can cause inflammation (peritonitis) and infection.
- Unexplained, persistent nausea or vomiting
- Unexplained weight loss
- Change in frequency or character of stool (bowel movements)
- Small-caliber (narrow) or ribbon-like stools
- Sensation of incomplete evacuation after a bowel movement
- Rectal pain: Pain rarely occurs with colon cancer and usually indicates a bulky tumor in the rectum that may invade surrounding tissue after moving through the colon's submucosa.
Studies suggest that the average duration of symptoms (from onset to diagnosis) is 14 weeks.
Colon Cancer Causes
Most colorectal cancers arise from adenomatous polyps. Such polyps are comprised of excess numbers of both normal and abnormal appearing cells in the glands covering the inner wall of the colon. Over time, these abnormal growths enlarge and ultimately degenerate to become adenocarcinomas.
People with certain genetic abnormalities develop what are known as familial adenomatous polyposis syndromes. Such people have a greater-than-normal risk of colorectal cancer.
- In these conditions, numerous adenomatous polyps develop in the colon, ultimately leading to colon cancer.
- There are specific genetic abnormalities found in the two main forms of familial adenomatous polyposis.
- The cancer usually occurs before age 40 years.
- Adenomatous polyposis syndromes tend to run in families. Such cases are referred to as familial adenomatous polyposis (FAP). Celecoxib (Celebrex) has been FDA approved for FAP. After six months, celecoxib reduced the mean number of rectal and colon polyps by 28% compared to placebo (sugar pill) 5%.
Another group of colon cancer syndromes, termed hereditary nonpolyposis colorectal cancer (HNPCC) syndromes, also run in families. In these syndromes, colon cancer develops without the precursor polyps.
- HNPCC syndromes are associated with a genetic abnormality. This abnormality has been identified, and a test is available. People at risk can be identified through genetic screening.
- Once identified as carriers of the abnormal gene, these people require counseling and regular screening to detect precancerous and cancerous tumors.
- HNPCC syndromes are sometimes linked to tumors in other parts of the body.
Also at high risk for developing colon cancers are people with any of the following:
- Ulcerative colitis or Crohn's colitis (Crohn's disease)
- Breast, uterine, or ovarian cancer now or in the past
- A family history of colon cancer
The risk of colon cancer increases two to three times for people with a first-degree relative (parent or sibling) with colon cancer. The risk increases more if you have more than one affected family member, especially if the cancer was diagnosed at a young age.
Other factors that may affect your risk of developing a colon cancer:
- Diet: Whether diet plays a role in developing colon cancer remains under debate. The belief that a high-fiber, low-fat diet could help prevent colon cancer has been questioned. Studies do indicate that exercise and a diet rich in fruits and vegetables can help prevent colon cancer.
- Obesity: Obesity has been identified as a risk factor for colon cancer.
- Smoking: Cigarette smoking has been definitely linked to a higher risk for colon cancer.
- Drug effects: Recent studies have suggested postmenopausal hormone estrogen replacement therapy may reduce colorectal cancer risk by one-third. Patients with a certain gene that codes for high levels of a hormone called 15-PGDH may have their risk of colorectal cancer reduced by one-half with the use of aspirin.
Colorectal cancer is the third most common non-skin cancer diagnosed in men and women in the U.S. It is also the second highest cause of cancer deaths. Still, colorectal cancer is highly curable when it is detected early enough. Colorectal cancer is a result of cancer cells that form in the lining of the colon (large intestine) or rectum.
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.