Colon cancer begins when the cells of the intestinal lining change and start to reproduce in an uncontrolled manner, resulting in the growth of tumors. These masses of cells can block the colon and prevent it from functioning properly. In metastatic colon cancer, also called advanced colon cancer or stage IV colon cancer, these cancerous cells spread to other parts of the body.
You may sometimes hear colon cancer referred to as "colorectal" cancer. This term simply means that cancer starts in either the colon or the rectum, which together make up the large intestine. As a key part of the gastrointestinal (GI) tract, the large intestine helps the body process and eliminate waste.
Most tumors that begin in the colon start as slower-growing polyps. Some of these are benign or non-spreading. Adenomatous polyps, or adenomas, can become cancerous and eventually spread to other parts of the body as metastatic colon cancer. These adenocarcinomas are the most common type of tumor found in colon cancer cases.
About 4.1% of men and women in the U.S.¹ will be diagnosed with colon cancer at some point in their lives.
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Colon cancer can produce symptoms that mimic other types of GI tract illnesses. These include:
Pain and tenderness in the abdomen
Unusual and ongoing changes in bowel habits like diarrhea or constipation
Thin or narrow stools
Weight loss without an obvious cause
The term metastatic means that cancer has spread from its origin to other places in the body. Why does this happen with colon cancer, and where is cancer most likely to spread?
First, colon cancer takes some time to develop from a polyp to a malignant tumor. Researchers at the Howard Hughes Medical Institute who studied mutations in colon cancer cells found that it can take as long as 17 years² for an adenoma, or small polyp, to become a carcinoma. However, the development of a tumor to its spread throughout the body can take as little as two years.
Colon cancer passes through several stages before it becomes metastatic.
Stage 0. The cancer is still in the form of small polyps and has not grown beyond the lining of the intestine. It can usually be removed with surgery.
Stage I. Polyps have grown deeper into the colon wall but have not spread. Surgery can remove these small tumors, especially if the cancerous cells are not at the edges of the polyp. If the cancer is not confined to a small polyp, a section of the intestine may need to be removed.
Stage II. Tumors have grown through the intestinal wall but have not yet spread to the lymph nodes or other organs. Surgical removal of a portion of the colon and surrounding lymph nodes may be necessary. If your doctor suspects that not all the cancerous cells were removed, they may recommend chemotherapy.
Stage III. Cancer cells have spread to the surrounding lymph nodes but not to other parts of the body. Surgical removal of part of the colon and lymph nodes should be followed by chemotherapy and possibly radiation treatments.
Stage IV. This is the metastatic stage of colon cancer, where cancerous cells have spread to other organs. Surgery may be recommended to remove tumors but is almost always followed by chemotherapy and radiation.
With many types of colorectal cancer, the liver is the most likely place for cancer to spread first. Cancer in the liver can cause jaundice, nausea, and swelling in the extremities as the body becomes inefficient at filtering toxins. Other common places for colon cancer to spread include the lungs, brain, and peritoneum (abdominal cavity lining).
Once you have reached stage IV colon cancer, the treatment required almost always includes chemotherapy and radiation. Surgery to remove the largest tumors in the colon can be beneficial, but it's often impossible to find and remove the smaller cancers that have spread to other organs.
Many doctors will suggest starting treatment with neoadjuvant chemotherapy to shrink tumors wherever they are located in the body. Then, surgery can be used as a follow-up to take out the smaller tumors. It may also be necessary to surgically implant a stent (hollow tube) in the intestine to permit the passage of waste through the cancerous areas.
In other cases, the colon is removed during a surgery called a colostomy. In a colostomy, the large intestine above the level of the cancer is taken out, and the end is surgically attached to an opening in the skin on the lower abdominal area. This opening is commonly connected to an exterior bag for waste to pass into.
Targeted treatment is another option for colon cancer. Specific drugs can be used that interfere with the tumor's ability to grow. These medications are usually administered intravenously at the same time as chemotherapy treatments designed to shrink tumors. The exact drugs used depend on the type of tumor you have and where it is located.
As the third most common cancer among men and women in the U.S., colorectal cancer impacts nearly 150,000 people every year. It is the second leading cause of death³ in the U.S. About 63% of people diagnosed with colon cancer at any stage are alive after five years.
Other interesting facts⁴ about colon cancer:
25% to 30% of people with colorectal cancer have a family history of the disease.
Black Americans are more likely to be diagnosed and die from colorectal cancer than other groups.
Early screening has decreased the number of cases overall since the mid-1980s.
The colorectal cancer death rate dropped by 55% between 1970 and 2018 because of better screening and treatments.
If everyone eligible was screened, more than 68% of deaths could be avoided.
Because the most common type of colon cancer, adenocarcinoma, is relatively slow-growing, the earlier that polyps or tumors are discovered, the better the outcomes are. This is why medical professionals recommend that people over 45 have a colonoscopy, where a small camera is inserted into the intestinal tract to look for polyps proactively.
However, once colon cancer has spread to other parts of the body, survival rates are lowered. Cancer cases are tracked in the SEER (Surveillance, Epidemiology, and End Results) database and are separated not by numbered stages but by where cancer has spread.⁵
Localized: cancer has not spread beyond the intestinal wall; 91% survival rate after five years.
Regional: cancer has spread to lymph nodes or nearby tissue; 72% survival rate after five years
Distant: cancer has spread to other organs; 14% survival rate after five years
Metastatic colon cancer is considered distant and has the lowest survival rates. Still, your age, your overall health, and how and where cancer has spread can all play a big role in your ability to overcome the disease.
Cancer Stat Facts: Colorectal Cancer | NIH: National Cancer Institute
Colon Cancer's Potential for Metastasis Determined Early | Howard Hughes Medical Institute
Colorectal Cancer: Statistics | Cancer.Net
Facts and Stats | Fight Colorectal Cancer
Survival Rates for Colorectal Cancer | American Cancer Society