About colorectal cancer

Colorectal Cancer Basics

Diagram of different parts of the colon
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What is colorectal cancer?

Colorectal cancer (CRC), also known as bowel cancer, includes colon cancer and rectal cancer. It is characterized by tumors (tumours) that occur in the colon or rectum. The colon and rectum are part of the large intestine. The mouth, esophagus, stomach, small intestine, large intestine, and anus make up the gastrointestinal tract portion of the digestive system. The gastrointestinal tract absorbs nutrients and water from the food you eat and gets rid of waste from the body through bowel movements.

If you have recently been diagnosed with colorectal cancer, you are not alone. Globally, nearly 2 million people were diagnosed with colorectal cancer in 2020. It is the third most common type of cancer worldwide, following only lung cancer and prostate cancer in men, and lung cancer and breast cancer in women.

There is a common misconception that colorectal cancer is a disease of elderly, white males. But CRC affects women and men equally. It affects people of all races and ethnicities; in fact, African Americans are 20% more likely to get colorectal cancer. And while CRC occurs mostly in people over 50 years old, the incidence of early-onset colorectal cancer, diagnosed in patients under age 50, is increasing. The International Agency for Research on Cancer predicts that by 2040, 200K people aged 25-49 will be diagnosed with CRC annually. In the United States, colorectal cancer is now the leading cause of cancer deaths for people 20-49 years old. In response to this alarming trend, some institutions, like the American Cancer Society (ACS), have adjusted the age at which they recommend patients start CRC screening. For patients with an average risk of CRC, the ACS recommends screening begin at age 45.

Colorectal cancer is the second most common cause of cancer death worldwide. There are nearly 1 million deaths annually. However, there is hope to reduce mortality and increase the survival rate of colorectal cancer through regular screening, early detection, and the development of new treatments.

Most colorectal cancers start out as precancerous colorectal polyps, also known as adenomas or adenomatous polyps, which are abnormal growths inside the colon or rectum. When colorectal polyps are discovered by screening tests like colonoscopy, they can be removed, and colorectal cancer can be prevented. Even when precancerous polyps have become cancer, CRC discovered in the early stages is highly treatable. At more advanced stages, CRC can still be cured with appropriate combinations of surgery, chemotherapy and targeted drug therapy, and radiation therapy. In the most difficult cases — when cancer has metastasized (spread) to the liver, lungs, or other parts of the body — treatment can prolong survival time and improve quality of life. People are living longer than ever with CRC because the number and quality of treatment options are increasing.

What are the symptoms of colorectal cancer?

Changes in bowel habits, such as constipation or diarrhea, or a change in the stool itself
Rectal bleeding
Blood in or on the stool (bowel movement)
Unintentional or unexplained weight loss
Abdominal pain 
or bloating

If you have any of these symptoms, please talk to your doctor or other healthcare provider.

How is colorectal cancer diagnosed?

When a person has no symptoms, CRC is diagnosed through colorectal cancer screening, also known as colon cancer screening. The decision to do CRC screening is made between a person and their healthcare team and is based on a number of factors including professional guidelines, age, personal and lifestyle risk factors, familial risk factors, and personal preference. 60% of colorectal cancer deaths could be prevented with regular colorectal cancer screening.

When a person has symptoms that suggest the possibility of colorectal cancer, they will have diagnostic testing to look for CRC. This can include some of the same tests as screening, like colonoscopy or sigmoidoscopy, as well as biopsy (tissue sampling), and imaging tests like CT scan, MRI scan, or PET scan.

When colorectal cancer is diagnosed, staging is one way oncologists assess prognosis and plan the best course of treatment. Stage describes the extent of the cancer, and includes factors like tumor size, whether there is cancer in nearby lymph nodes, and whether cancer has spread to other parts of the body (metastasis).

Cancer stages

Cancer stage
What it means
Also known as
Stage 0Cancer cells are limited to the inner layer of the colon or rectum.Carcinoma in situ (CIS), adenocarcinoma in situ
Stage I (stage 1)Cancer is localized to the wall of the colon or rectum and has not spread to lymph nodes or other organs or tissues.Early-stage cancer
Stage II (stage 2)Cancer has grown into or through the wall of the colon or rectum but has not spread to lymph nodes.Early-stage cancer
Stage III (stage 3)Cancer has grown and/or it has spread to lymph nodes or invaded surrounding tissues.Advanced stage cancer
Stage IV (stage 4)Cancer has spread to distant parts of the body, such as liver or lungs.Metastatic cancer, advanced stage cancer

Can colorectal cancer be prevented?

There are lifestyle factors including diet, physical activity, smoking, and alcohol consumption, that you can change to reduce your risk of colorectal cancer.

Colorectal cancer is somewhat unusual in that it can be prevented by diagnosing and removing colon polyps before they become cancerous. This is done by regular colorectal cancer screening.

It is important to discuss colon cancer screening with your doctor. Together, you and your healthcare team can look at your risk factors to determine when and how you should begin CRC screening. This includes lifestyle risk factors, age, obesity, ethnicity, history of inflammatory bowel disease like Crohn's disease or ulcerative colitis, as well as familial risk factors like family history of colorectal cancer, and hereditary syndromes of increased CRC risk like Lynch syndrome or familial adenomatous polyposis.

Next article: Colorectal Cancer Screening