What is Colorectal Cancer?

As we come to the end of Colon Cancer Awareness Month, here at Cancer Pro, we thought it might make sense to take some time to understand better the colon and its function in the body. Plus, at the same time, remind ourselves of what we mean by Colon or Colorectal cancer (as it is sometimes known), along with some of the risk factors and causes of colon cancer.

What is the colon, and how does it function?

The colon and the rectum are the final portions of the long tube that extends from our mouth to our anus. When we eat, food enters our mouth, chewed, and then swallowed; from there, it travels through the esophagus and into the stomach.

The food is ground into smaller particles in the stomach and then carefully enters the small intestine. In the small intestine, the final digestion of food and absorption of the food’s nutrients occurs.

The food that is not digested and absorbed enters the large intestine (colon) and, finally, the rectum.

Essentially the large intestine acts as a waste storage facility where additional water, salts, and some vitamins are further removed. Some undigested food, like fibre, is digested by colonic bacteria, and some of the products of digestion are absorbed from the colon and into the body.

Approximately 10% of all the energy we derive from food comes from bacterial digestion products in the colon.

The remaining undigested food, dying cells from the lining of the intestines, and large numbers of bacteria are stored in the colon and then periodically passed into the rectum. Their arrival into the rectum initiates a bowel movement that empties the body’s colonic contents as a stool.

The large intestine is a tube, which is more like a steel-belted radial tyre than a garden hose and comprises four layers. The first is an inner layer of cells that line the cavity through which the undigested and digesting food travels, called the mucosa. The mucosa is attached to a thin second layer, the submucosa attached to a layer of muscle, the muscularis. The entire tube is enclosed by fibrous (scar-like) tissue called the serosa.

The most common cancers of the large intestine (the type called adenocarcinoma) arise from the mucosa, the cell’s inner layer. These cells are exposed to toxins from food and bacteria, and mechanical wear and tear are turning over rapidly (dying off and being replaced).

Mistakes involving genes within the replacement cells lead to abnormal cells and uncontrolled proliferation of the abnormal cells that give rise to cancer. The rapid turnover allows for more mistakes to occur than tissues that do not turn over so rapidly (for example, liver tissue).

What is colorectal cancer?

Cancers of the colon and rectum (colorectal cancer) start when the standard replacement of colon lining cells goes astray. Because mistakes in cell division occur frequently and for reasons that we don’t fully understand, sometimes errors occur that escape our editing systems. When this happens, these cells begin to divide independently of the regular checks and balances that control growth.

As these abnormal cells grow and divide, they can lead to growths within the colon called polyps. Polyps vary in type, but many are precancerous tumours that grow slowly over time and do not spread.

As polyps grow, additional genetic mutations further destabilise the cells. When these precancerous tumours change direction (extending into the tube wall rather than into the space in the middle of it) and invade other layers of the large intestine (such as the submucosa or muscular layer), the precancerous polyp has become cancerous.

In most cases, this process is slow, taking at least eight to 10 years to develop from those early aberrant cells to frank cancer. Colorectal cancer is typically an adenocarcinoma, a term that refers to cancer formed in certain types of lining tissues in the body.

Once colorectal cancer forms, it begins to grow in two ways. First, it can grow locally and extend through the intestine wall and invade adjacent structures, making the mass (called the primary tumour) more challenging and harder to remove. The local extension can cause additional symptoms such as pain or fullness, perforation of the colon, or blockages of the colon or nearby structures.

Second, as cancer grows, it begins the metastasis process, shedding thousands of cells a day into the blood and lymphatic system that can cause cancers to form in distant locations. Colorectal cancers most commonly spread first to local lymph nodes before travelling to distant organs.

Once local lymph nodes are involved and spread to the liver, the abdominal cavity and the lung are the most common metastatic spread destinations.

What are the risk factors and causes of colon cancer?

Health care professionals are confident that colorectal cancer is not contagious (a person cannot catch the disease from a cancer patient); however, some people are more likely to develop colorectal cancer than others.

The factors that increase a person’s risk of colorectal cancer include, among others, increasing age, ethnicity, high fat intake, smoking and drinking along with a family history of colorectal cancer and polyps, together with the presence of polyps in the large intestine, and inflammatory bowel diseases such as primarily chronic ulcerative colitis.

About Cancer Pro

Cancer Pro is the voice of the world’s cancer physicians and oncology professionals in Malaysia and is the trusted compassionate resource for people with cancer, their families and caregivers. For more information regarding all aspects of colon and colorectal cancer along with the treatments currently available, please visit www.cancer-pro.com.