Colorectal Cancer begins in the rectum or colon. It can also sometimes be known as rectal cancer or colon cancer – based on its starting location. Rectal and colon cancer share many similarities. In this article, they are spoken about together. Treatment, however, will be discussed separately.
Healthy Digestive System
Both the rectum along with the colon belong to the digestive system. This is also known as the GI or gastrointestinal system – as shown in the illustration. In the early stages of the digestive tract – the small intestine and stomach – food is processed and used for energy. The latter part – the rectum and colon – takes fluid and forms it into solid waste – otherwise known as stool or fecal matter – which then leaves the body. If you wish to understand more about colorectal cancer, learning about how a healthy digestive system works is a good idea.
Once food has been processed by the mouth, it moves down the esophagus to your stomach. At that point, it is broken down partially and sent further down until it reaches the small intestine – the small bowel. It’s known as such as it is more narrow than the large intestine (which is the rectum and colon). Interestingly, even though it’s narrower, it’s the longer of the two, reaching to 20 feet or so. This is where most of the food gets broken down, and the majority of all the nutrients are absorbed from.
Once in the lower abdomen, the small intestine meets up with the large one. The large intestine stretches out about five feet and is mainly a tube that is muscular – the colon. Absorbing salt and water from food, the colon acts as a waste storage place.
Four Section Colon
The ascending colon is the first part of the colon. It begins with the cecum (a tiny pouch.) This is where the colon attaches on to the small bowel, extending upward toward the right of the abdomen. Also, the colon affixes to the appendix here.
Secondly, is the transverse colon. So named because it crosses the body, starting on the right and moving left.
Third is the descending colon, which continues down the left side.
Last and fourth is the sigmoid colon, named from its sigmoid or “S” shape.
The leftover waste after traveling throughout the colon is known as stool or feces. This is pushed along to the last 6 inches – the rectum – where it waits to be passed from the body out of the anus.
Both the rectum and colon wall are layered (see accompanying illustration located at the staging section). The most inner layer is where colorectal cancer begins. It can work its way through all or just some of the layers. It a good idea to understand a bit about these different layers as the stage of the cancer (extent of the spread) hinges to a large part on how deep it moves into the layers.
Unusual rectum or colon growths
The majority of these types of cancers grow slowly over a period of years. Previous to it becoming cancer, a tumor or abnormal tissue growth starts on the rectum or colon’s inner lining as a polyp that is non-cancerous. Tumors (which may either be benign or cancerous) are abnormal tissues. A polyp is a tumor that is non-cancerous. Sometimes polyps change and become cancerous, however, not all of them. The type of polyp determines the chance it has of turning cancerous. There are a couple of polyp types:
Adenomatous polyps (adenomas) – these are the type that can become cancerous. They’re known as pre-cancerous.
Hyperplastic and inflammatory polyps usually don’t become pre-cancerous. There are some in the medical community who believe that some of these can indeed turn into pre-cancerous polyps. They may also pose a higher risk of becoming adenomas or even cancer, especially if they’re growing in the ascending colon.
Dysplasia is another condition that is considered pre-cancerous. When studied through a microscope, these cells that are in the rectum or colon lining don’t look normal – however, they don’t look like real cancer cells. They can change and become cancer with time. Those who have suffered diseases like Crohn’s or ulcerative colitis for some years are more at risk for it. Both diseases have the effect of inflaming the colon chronically.
Colorectal Cancer – How it Begins and Spreads
Now that you know what is colon cancer, let us start with how it begins and spreads over time. Colorectal cancer that starts inside a polyp can start to expand into the rectum or colon wall. Embedded into the wall, cancer can form lymph vessels or blood vessels. The lymph vessels are very small channels that handle whisking fluid and waste away. Their first stop are lymph nodes that contain infection-fighting immune cells. Once cancer has spread into the lymph or blood vessels, they very easily can move about to other lymph nodes or even distant places like the liver. The spreading of the cancer to other places in the body is termed metastasis.
Various Types of Rectum and Colon Cancer
Adenocarcinomas: Most colorectal cancers (greater than 95%) are this type. They begin inside cells that create glands inside which mucus for lubrication of the rectum or colon is made. If a doctor is talking about colorectal cancer, they’re more than likely referring to this.
A few other tumors can also begin in the rectum and colon. Some of these are:
These come from special intestine cells that produce hormones.
- Gastrointestinal stromal tumors (GISTs):
These are special colon wall cells that are named the interstitial cells of Cajal. Some of them are cancerous, and others aren’t. They are usually not found in the colon, but can be discovered in the digestive system.
Immune cells which are cancerous. Generally, they begin in the lymph nodes. However, can also begin in the rectum, colon or possibly other organs.
This cancer can be found in the blood vessels along with being found in connective tissue and muscle along the rectum and colon walls. They are fairly rare.