Colorectal Cancer

What Is Colorectal Cancer?

Colorectal cancer starts in the colon or the rectum. These cancers can also be called colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common. Cancer starts when cells in the body start to grow out of control. To learn more about how cancers start and spread.

The colon and rectum

To understand colorectal cancer, it helps to know about the normal structure and function of the colon and rectum.

The colon and rectum make up the large intestine (or large bowel), which is part of the digestive system, also called the gastrointestinal (GI) system .

Most of the large intestine is made up of the colon, a muscular tube about 5 feet (1.5 meters) long. The parts of the colon are named by which way the food is traveling through them.

1. • The first section is called the ascending colon. It starts with a pouch called the cecum, where undigested food comes in from the small intestine. It continues upward on the right side of the abdomen (belly).
2. • The second section is called the transverse colon. It goes across the body from the right to the left side.
3. • The third section is called the descending colon because it descends (travels down) on the left side.
4. • The fourth section is called the sigmoid colon because of its “S” shape. The sigmoid colon joins the rectum, which then connects to the anus.

The ascending and transverse sections together are called the proximal colon. The descending and sigmoid colon are called the distal colon.

How do the colon and rectum work?

The colon absorbs water and salt from the remaining food matter after it goes through the small intestine (small bowel). The waste matter that's left after going through the colon goes into the rectum, the final 6 inches (15cm) of the digestive system. It's stored there until it passes through the anus. Ring-shaped muscles (also called a sphincter) around the anus keep stool from coming out until they relax during a bowel movement.

How does colorectal cancer start?

Polyps in the colon or rectum

Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are called polyps.

Some types of polyps can change into cancer over time (usually many years), but not all polyps become cancer. The chance of a polyp turning into cancer depends on the type of polyp it is. There are different types of polyps.

1. • Adenomatous polyps (adenomas): These polyps sometimes change into cancer. Because of this, adenomas are called a pre-cancerous condition. The 3 types of adenomas are tubular, villous, and tubulovillous.
2. • Hyperplastic polyps and inflammatory polyps: These polyps are more common, but in general they are not pre-cancerous. Some people with large (more than 1cm) hyperplastic polyps might need colorectal cancer screening with colonoscopy more often.
3. • Sessile serrated polyps (SSP) and traditional serrated adenomas (TSA): These polyps are often treated like adenomas because they have a higher risk of colorectal cancer.

Other factors that can make a polyp more likely to contain cancer or increase someone’s risk of developing colorectal cancer include:

1. • If a polyp larger than 1 cm is found
2. • If more than 3 polyps are found
3. • If dysplasia is seen in the polyp after it's removed. Dysplasia is another pre-cancerous condition. It means there's an area in a polyp or in the lining of the colon or rectum where the cells look abnormal, but they haven't become cancer.

How colorectal cancer spreads

If cancer forms in a polyp, it can grow into the wall of the colon or rectum over time. The wall of the colon and rectum is made up of many layers. Colorectal cancer starts in the innermost layer (the mucosa) and can grow outward through some or all the other layers .

When cancer cells are in the wall, they can then grow into blood vessels or lymph vessels (tiny channels that carry away waste and fluid). From there, they can travel to nearby lymph nodes or to distant parts of the body.

The stage (extent of spread) of a colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum.

Risk Factors

A risk factor is anything that raises your chances of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like a person’s age or family history, can’t be changed.

But having a risk factor, or even many, does not mean that you will get the disease. And some people who get the disease may not have any known risk factors.

Researchers have found several risk factors that might increase a person’s chance of developing colorectal polyps or colorectal cancer.

Colorectal cancer risk factors you can change

• Colorectal cancer risk factors you can change

Being overweight or obese

If you are overweight or obese (very overweight), your risk of developing and dying from colorectal cancer is higher. Being overweight raises the risk of colon and rectal cancer in people, but the link seems to be stronger in men. Getting to and staying at a healthy weight may help lower your risk.

Not being physically active

If you're not physically active, you have a greater chance of developing colon cancer.

Certain types of diets

A diet that's high in red meats (such as beef, pork, lamb, or liver) and processed meats raises your colorectal cancer risk. Cooking meats at very high temperatures (frying, broiling, or grilling) creates chemicals that might raise your cancer risk. It’s not clear how much this might increase your colorectal cancer risk.

Having a low blood level of vitamin D may also increase your risk.

Following a healthy eating pattern that includes plenty of fruits, vegetables, and whole grains, and that limits or avoids red and processed meats and sugary drinks probably lowers risk.

Smoking

People who have smoked tobacco for a long time are more likely than people who don't smoke to develop and die from colorectal cancer. Smoking is a well-known cause of lung cancer, but it's linked to a lot of other cancers, too..

Alcohol use

Colorectal cancer has been linked to moderate to heavy alcohol use. Even light-to-moderate alcohol intake has been associated with some risk. It is best not to drink alcohol. If people do drink alcohol, they should have no more than 2 drinks a day for men and 1 drink a day for women. This could have many health benefits, including a lower risk of many kinds of cancer.

A personal history of colorectal polyps or colorectal cancer

If you have a history of adenomatous polyps (adenomas), you are at increased risk of developing colorectal cancer. This is especially true if the polyps are large, if there are many of them, or if any of them show dysplasia.

If you've had colorectal cancer, even though it was completely removed, you are more likely to develop new cancers in other parts of the colon and rectum. The chances of this happening are greater if you had your first colorectal cancer when you were younger.

A personal history of inflammatory bowel disease

If you have inflammatory bowel disease (IBD), including either ulcerative colitis or Crohn’s disease, your risk of colorectal cancer is increased.

IBD is a condition in which the colon is inflamed over a long period of time. People who have had IBD for many years, especially if untreated, often develop dysplasia. Dysplasia is a term used to describe cells in the lining of the colon or rectum that look abnormal, but are not cancer cells. They can change into cancer over time.

If you have IBD, you may need to start getting screened for colorectal cancer when you are younger and be screened more often. Inflammatory bowel disease is different from irritable bowel syndrome (IBS), which does not appear to increase your risk for colorectal cancer.

A family history of colorectal cancer or adenomatous polyps

Most colorectal cancers are found in people without a family history of colorectal cancer. Still, as many as 1 in 3 people who develop colorectal cancer have other family members who have had it.

People with a history of colorectal cancer in a first-degree relative (parent, sibling, or child) are at increased risk. The risk is even higher if that relative was diagnosed with cancer when they were younger than 50, or if more than one first-degree relative is affected.

The reasons for the increased risk are not clear in all cases. Cancers can “run in the family” because of inherited genes, shared environmental factors, or some combination of these.

Having family members who have had adenomatous polyps is also linked to a higher risk of colon cancer. (Adenomatous polyps are the kind of polyps that can become cancer.)

If you have a family history of adenomatous polyps or colorectal cancer, talk with your doctor about the possible need to start screening before age 45. If you've had adenomatous polyps or colorectal cancer, it’s important to tell your close relatives so that they can pass along that information to their doctors and start screening at the right age.

Having an inherited syndrome

About 5% of people who develop colorectal cancer have inherited gene changes (mutations) that cause family cancer syndromes and can lead to them getting the disease.

The most common inherited syndromes linked with colorectal cancers are Lynch syndrome (hereditary non-polyposis colorectal cancer, or HNPCC) and familial adenomatous polyposis (FAP), but other rarer syndromes can increase colorectal cancer risk, too.

Having type 2 diabetes

People with type 2 (usually non-insulin dependent) diabetes have an increased risk of colorectal cancer. Both type 2 diabetes and colorectal cancer share some of the same risk factors (such as being overweight and physical inactivity). But even after taking these factors into account, people with type 2 diabetes still have an increased risk. They also tend to have a less favourable prognosis (outlook) after diagnosis.