Colon Cancer and Rectal Cancer Facts
What Is Colorectal Cancer?
The colon, which makes up most of the large intestine, is a muscular tube about five feet long, shaped like a giant question mark, with a smooth inner lining. When you eat food, it travels from the stomach and through the small intestine — where it is digested and absorbed — then through the colon, where any leftover water and salt are absorbed.
The last six inches of the large intestine comprise the rectum — where waste is stored before it leaves the body — and the anus.
Colorectal cancer occurs when something goes wrong with cells in the colon or rectum, causing them to grow out of control. Taken together, cancer of the colon and rectum accounts for more than 150,000 new diagnoses in the U.S. each year.
- Colon cancer starts in the smooth inner lining, or mucosa, after developing from a precancerous polyp. Tumors can grow deeper into the colon wall and spread into lymph nodes and other organs.
- About 1 in 21 men and 1 in 23 women will get colorectal cancer during their lifetimes.
- Colorectal cancer is the third-leading cause of cancer death both in women (after breast and lung cancer) and in men (after lung and prostate cancer). However, the death rate from colorectal cancer has been dropping steadily over the last few decades, most likely due to better screening and treatment.
Stages of Colorectal Cancer
After a diagnosis of colorectal cancer, doctors will order additional tests to define the cancer stage. The stage is a key factor for defining specific treatment recommendations.
The stages of colorectal cancer are:
- Stage 0: This is a precancerous polyp. At this point, rapidly growing cells have not reached beyond the inner lining of the colon or rectum.
- Stage 1: The cancer has spread further into the colon or rectum but has not spread to nearby lymph nodes or other organs.
- Stage 2: The cancer has grown into the outermost layers of the colon or rectum and may have grown into nearby organs, but has neither spread to lymph nodes nor other organs in the body.
- Stage 3: The cancer has spread to nearby lymph nodes but has not spread to distant sites in the body.
- Stage 4: The cancer has spread to distant organs, such as the liver or lung.
Types of Colorectal Cancer
Other types of cancer that can start in the colon and rectum are much less common:
- Gastrointestinal stromal tumors (GISTs) start in special cells found in the wall of the gastrointestinal tract, called the interstitial cells of Cajal. These cells play a role in the autonomic nervous system, which regulates automatic body processes, such as digestion. GISTs can form in the stomach or anywhere along the digestive tract, but they rarely occur in the colon.
- Lymphomas are cancers that typically start in immune system cells, but can also start in the colon, rectum or other organs.
- Neuroendocrine or carcinoid tumors start in specialized hormone-making cells called neuroendocrine cells that are scattered throughout the intestine and other organ systems. These tumors are sometimes called neuroendocrine tumors.
- Sarcomas are rare cancers that can start in blood vessels, muscle or connective tissue in the wall of the colon and rectum.
How Colon Cancer Develops
Getting colorectal cancer means abnormal cells in your colon or rectum are growing and dividing at a rapid pace — so fast that cells in your immune system that fight disease cannot keep up.
The problem begins with the human genetic code and all its complexity. Every time a cell divides, there’s an extremely small risk that an error will occur when the DNA get copied. If DNA is like a book, a mutation is a typo that happens in the copying process.
The cells of the colon and rectum naturally turn over more often than many other types of cells. With all that cell division, the risk of such a typo increases.
Many mutations don’t cause harm, and the abnormal cells are eliminated by the body. Unfortunately, some mutations evade elimination and become cancer. The biochemical signals that normally would stop these cells from growing get turned off. Further changes in these cells will follow, in order to help the tumor cells survive.
Here’s what happens on a larger scale: Layers of tissue inside the colon and rectum form what is called the wall. The innermost layer of that wall, called the mucosa, is where colorectal cancer usually starts.
When cells in the mucosa are affected by the wrong mutation, they grow uncontrollably and join together to form a small, bulb-like growth called a polyp. Most polyps are benign, which means they do not cause cancer, but some can turn into cancer over time.
There are three main types of polyps:
- Adenomatous polyps: The most common type of polyp, also called an adenoma. The cells that form these polyps grow and divide abnormally compared with normal colon cells, but only sometimes become cancer.
- Hyperplastic polyps: Cells in this type of polyp grow fast but rarely become cancer. This is a common type of polyp and usually is found in the lower part of the colon or rectum.
- Inflammatory polyps: These often appear after about with inflammatory bowel disease. They rarely become cancer.
If it is caught early through routine screening, colorectal cancer is very treatable. In more advanced cases, cancer cells will have grown through the colon wall and eventually spread to other parts of the body — a process called metastasis. Colorectal cancer that has metastasized tends to travel through the blood or lymph system, to the liver, lung and peritoneum.
What Increases Your Risk of Colon Cancer?
A risk factor is something that increases your chances of developing a disease. Some risk factors for colorectal cancer are things you’re born with or other things, like age, that you cannot control. Yet many lifestyle choices can also raise or lower your risk of developing the disease. Factors such as diet, weight and exercise, for instance, are strongly linked to colorectal cancer.
- About 70% of colorectal cancers arise with no history of cancer in the patient’s family.
- Another 5% are caused by known genetic syndromes.
- The remaining 25% occur in people with a family history, but the exact factor that causes it — genetic and environmental — are currently unknown.
Controllable Risk Factors for Colon Cancer Include:
- Overweight or obesity, especially excess fat around the waist
- Physical inactivity
- Type 2 diabetes
- Cigarette smoking
- Drinking alcohol excessively
- A diet high in red, processed or charred meats
- Low vitamin D levels
Uncontrollable Risks for Colon Cancer Include:
- Personal history of colorectal polyps
- Personal history of inflammatory bowel disease such as ulcerative colitis or Crohn’s disease
- Family history of colorectal polyps
- Family history of cancer of the colon, rectum, ovary, endometrium or breast
- Being of African American or Ashkenazi Jewish descent
- Having an inherited syndrome associated with colorectal cancers, including:
- Lynch syndrome
- Familial adenomatous polyposis
- Turcot syndrome
- MUTYH-associated polyposis
- Peutz-Jeghers syndrome
Genetic testing can help identify inherited gene changes that increase your risk of colorectal cancer. As research reveals more about the genes behind colorectal cancer, these tests will help more and more people.
Hereditary Causes of Colorectal Cancer
Having close relatives with colorectal cancer increases the risk of developing the disease (and being diagnosed earlier in life) and could direct or change the treatment for some patients. Up to 10% of people with colorectal cancer have an inherited genetic abnormality that is associated with developing the disease.
Two of the most common inherited conditions that influence your risk of disease include:
- Lynch syndrome is a condition that increases the risk of colorectal and other cancers — including stomach, liver, ovarian, endometrial, brain, skin and small intestine cancers. The syndrome is also referred to as hereditary nonpolyposis colorectal cancer.
- Familial adenomatous polyposis involves developing multiple noncancerous polyps in the colon early in life that may later progress to colorectal cancer. This condition appears at a much earlier age than normally developing colorectal cancers.
Although hereditary factors account for less than 5% of colorectal cancers, your chances of having one of these conditions are higher if several of your close family members have been diagnosed.
If your family history suggests an increased risk of colorectal cancer, City of Hope’s hereditary colorectal cancer multidisciplinary program offers genetic counseling and screening that can identify whether inherited conditions influence your risk — and guide you to the best treatments.
Colon Cancer Prevention
More than most other cancers, colorectal cancer is affected by things you can control, like what you eat and how much you exercise. Eating a diet that includes plenty of vegetables, fruits and whole grains — and that is low in animal fat — has been linked with a lower risk of colorectal cancer. Other lifestyle changes like quitting smoking, drinking less and exercising regularly may help lower your risk.
And getting screened for colorectal cancer starting at age 50 (or younger if you have a family history) may help doctors to find and remove polyps before they turn into cancer.
What Are the Symptoms of Colorectal Cancer?
Colorectal cancer does not always cause symptoms during the early stages of the disease. Polyps can grow in the colon wall for months or years without causing bleeding or pain. Symptoms are more likely to appear during the later stages of disease, after the cancer has grown or spread.
Typical colorectal cancer symptoms include:
- A change in bowel habits (such as diarrhea, constipation or narrow stools) lasting more than a few days
- A persistent urge to have a bowel movement that doesn’t go away after you have one
- Bleeding of the rectum
- Blood in the stool (bright red or dark)
- Abdominal pain or cramping
- Bloating or a feeling of being full
- A diagnosis of anemia
- Weakness and fatigue
- Unintended weight loss
- Nausea or vomiting
Many of these symptoms can also be caused by noncancer conditions, such as hemorrhoids, irritable bowel syndrome, inflammatory bowel disease or infection. Still, if you have any of these problems for more than two weeks, it’s important to see your doctor right away so they can evaluate your symptoms and potentially rule out cancer or other serious conditions.