Colorectal cancer is a broad term to identify cancer that has afflicted certain parts of the digestive system. Normally, colon cancer develops in the latter parts of the digestive system – the colon (the longest part of the large intestine) and the rectum (the final part of the digestive tract, right before the anus). The origin of cancer determines how it is categorized, For example, if cancer starts in the colon, it is termed colon cancer; if it starts in the rectum, it is called rectal cancer. These two diseases have many characteristics in common and are often grouped under the definition of colorectal cancer. 

The incidence of colorectal cancer has historically been highest in adults over the age of 55. However, in the past decade, the number of diagnoses in older people has declined. This is largely attributable to increased regular screening and more people adhering to lifestyle choices that lower the risk of disease.

Unfortunately, according to the American Cancer Society, there has been an increasing trend among younger people, under the age of 55, being diagnosed with late-stage colorectal cancer.

In fact, the younger population is 58% more likely to be diagnosed with late-stage disease than older adults. This is troubling because the survival rate for late-stage colorectal cancer, where the cancer has spread to other parts of the body, is only 15%. The new guidance from The U.S. Prevention Task Force currently recommends colorectal cancer screening around age 45.

The Development of Colon Cancer

Most colorectal cancers develop from abnormal growths in the inner lining of the large intestine or the rectum, called polyps. Not all polyps evolve into cancer, but some can be considered precancerous. These are usually adenomatous polyps (adenomas), sessile serrated polyps (SSP), or traditional serrated adenomas (TSA). 

The following factors contribute to the likelihood of a polyp becoming cancer:

• If a polyp is larger than 1 cm.
• If more than three polyps are found in one patient.
• If dysplasia is observed after the removal of the polyp. Dysplasia is a precancerous condition. It represents an area in the lining of the colon or a polyp filled with abnormal cells that could become cancerous cells. 

On average, it takes a precancerous polyp several years (up to 15) to become cancerous. 

If colon cancer originates from a polyp, it can grow into the colon or rectum wall over time. It starts in the innermost layer called the mucosa and extends outward, occupying the other intestine wall layers. If cancer cells reach a blood vessel or a lymph vessel, they can travel through these channels and spread to nearby lymph nodes, other tissues, organs, or distant parts of the body.

Early Colorectal Cancer Symptoms and Signs

The early stages of colorectal cancer are often asymptomatic. Precancerous polyps also tend to go unnoticed. The symptoms and signs of colon cancer can be described as: 

• Unexplained weight loss
• Change in bowel habits that lasts for longer than five days (change in frequency of bowel movements, stool consistency such as watery stools, narrow stools, constipation, or diarrhea)
• Not feeling relieved after having a bowel movement
• Blood in the stool indicated by dark brown or black stool
• Bright red blood in the stool as a result of rectal bleeding
• Abdominal pain and cramps; loss of appetite
• Weakness and fatigue

There are many conditions other than colorectal cancer cause these symptoms, such as irritable bowel syndrome (IBS), hemorrhoids, or infection. It is vital to check with your healthcare provider if you are experiencing any of them for a prolonged period.

That said, digestive tract bleeding is a hallmark of colon cancer. Bleeding is evidenced by darker-colored stool. If bleeding persists, it could lead to anemia or a low red blood cell count. Therefore, low blood cell count is yet another potential indicator of colorectal cancer.

There are extreme cases, when no signs or symptoms are evident until the disease has spread to other parts of the body, such as the lungs or liver. Colorectal cancer that has spread outside of the colon is called metastatic colorectal cancer and often results in an enlarged liver, jaundice (yellowing of the whites of the eyes or the skin), and even breathing problems if it reaches the lungs.

Types of Colon Cancer

The most common colorectal types of cancer start in the mucus layer of the colon and rectum lining. They are called adenocarcinoma and include different subtypes, such as signet ring or mucinous adenocarcinoma. Some of these subtypes have worse outlooks than others.

Aside from adenocarcinomas, other types of colorectal cancer are:

• Carcinoid tumor – starts in cells that produce and release hormones in the intestine.
• Gastrointestinal stromal tumor (GIST) – begins in special cells called the interstitial cells of Cajal. GISTs can be found in different parts of the digestive system but are relatively rare in the colon.
• Sarcoma – starts in connective tissues of the colon and rectum wall, such as the muscle layers, blood vessels, etc. Sarcomas in the colorectal area are uncommon.
• Lymphoma – starts in the cells of the immune system. It can originate in lymph nodes but also in the colon, rectum, and other organs.

Survival Rates

The National Cancer Institute (NCI) collects information on 5-year survival rates for colon cancer, defined as 5-year relative survival rates. Relative means that the survival rate of people with a specific cancer type and stage compared to the overall population.

To understand relative survival rates, it is important to learn how colorectal disease is categorized when diagnosed. They are defined below:

• Localized: Cancer has not spread outside of the colon or rectum.
• Regional: Cancer has spread to nearby lymph nodes or structures.
• Distant: Cancer has spread to distant lymph nodes or distant parts of the body such as the liver or the lungs.

Survival rates per category shown reflect disease spread. They do NOT factor in the other variables such as patient’s age, overall health, how well cancer responds to treatment. 

Colon Cancer 5-Year Survival Rate

• Localized – 91%
• Regional – 72%
• Distant – 14%
• All stages combined – 63%

Rectal Cancer 5-Year Survival Rate

• Localized – 89%
• Regional – 72%
• Distant – 16%
• All stages combined – 67%

What to do if you recognize warning signs?

Colon cancer symptoms are nonspecific enough that they could be a sign of any number of different ailments. If you recognize any of the symptoms mentioned in this text, schedule a visit with your primary healthcare provider. It is likely that you will be provided guidance on the necessary examinations and screening methods to help determine the source of your symptoms. Colon cancer screening options include visual exams, such as X-rays or colonoscopy, and/or fecal testing (which is less invasive).

If you are older than 45 (or younger but with a high colon cancer risk because of family history or personal history of colon cancer or colorectal polyps), it is recommended you undergo routine screening every few years. If the disease is caught early, there’s a higher likelihood of a positive response to treatment and a better survival outcome. Treatment options may involve surgery, radiation therapy, chemotherapy, targeted therapy, immunotherapy.

Conclusion

Colorectal cancer is a beatable disease if caught early. Warning signs include unintentional weight loss, digestive issues, changes in bowel habits, weakness, and blood in the stool. It is imperative to visit a doctor immediately should you have persistent symptoms of colon cancer. It is also highly advised that those ages 45 and over, or those who are at risk of colorectal cancer, are routinely screened.

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