Cancer that develops in the large intestine is called colorectal cancer. There are a few stages that occur before colorectal cancer develops — such as genetic mutations and the development of polyps (outgrowths). The rate of colon cancer development depends on how soon these mutations and polyps appear.
In this article, we will discuss how colon cancer grows, its growth rate, the stages of colon cancer growth, and how patients with different stages fare.
How does colon cancer grow?
Colon cancer grows from the cells that make up the mucosa of the gut, which is its innermost layer. There are several types of cells that make up the gut. Some divide much more rapidly than others, which makes them prone to genetic errors during their division. This can cause them to divide uncontrollably — causing cancer.
In the colon, cells of the mucosa normally multiply rapidly to replace the ones lost daily. Sometimes, they grow into small outgrowths called polyps, which hang in the lumen of the gut. Some of these polyps have the potential to turn into cancer, which is how colon cancer grows.
Importantly, not all polyps are cancerous. Here is a brief overview of the different types:
- Adenomatous polyps: “Adeno” means gland. An adenomatous polyp is largely composed of cells that make up mucus-producing glands. They have the potential to turn into cancer cells, which is why they are also referred to as precancerous polyps.
- Hyperplastic polyps: Hyperplastic polyps are not cancerous. So they are also called benign polyps. Hyperplastic polyps are commonly found in the gut and are not dangerous. However, when found, your doctor might decide to do a biopsy as a precaution.
- Inflammatory polyps: Similar to hyperplastic polyps, inflammatory polyps are also benign and common.
- Serrated polyps: Serrated polyps have the potential to turn into colorectal cancer. Just like adenomatous polyps, they are also called precancerous polyps.
What’s the growth rate of colon cancer?
On average, a polyp in the gut will turn into colon cancer in 5-15 years. Once cancer develops, it grows at an average of 1 cm per year. Because of this slow growth rate, colon cancer often leads to no symptoms during the early stages of the disease. Only when cancer becomes large enough to bleed or obstruct the gut and cause constipation do patients show up.
What factors affect colon cancer growth?
The growth of colorectal cancer depends on a variety of factors, including genetics, diet, and lifestyle factors. This explains why colon cancer growth varies so widely between individuals. Some polyps turn into full-blown metastatic cancer within 5 years, while others take up to 15 years.
Here is a deeper dive into the risk factors that affect colorectal cancer growth:
- Genetics: Some people have genes that predispose them to colon cancer. For example, people with Lynch Syndrome and Familial Adenomatous Polyposis are more likely to develop precancerous polyps. This means colon cancer will appear at a much earlier age in these people compared to those with normal genes.
- Diet: Consuming certain foods can increase the risk of colon cancer, making it appear earlier than in other people. Foods high in sugar, processed meat, and animal fats all increase the risk of colon cancer.
- Smoking: Smoking is linked to several cancers, including colon cancer. Cigarette smoke is full of carcinogens (cancer-causing molecules), which make colon and rectal cancer more likely than in non-smokers.
- Inflammatory diseases: Inflammation makes you more vulnerable to genetic mutations, which are the root cause of cancer. Colon cancer in patients with inflammatory bowel disease appears at a younger age compared to those without gut inflammation.
- Obesity: Fat in the body can release leptin, a molecule that contributes to the development of colon cancer by causing inflammation. This is why obese people have a 1.3 times higher chance of developing colon cancer.
What are the stages of colon cancer?
Colorectal cancer stages are numbers given to identify how much it has spread. There are multiple ways to stage colon cancer, the most common being the TNM staging system.
TNM staging system
The TNM staging looks at three aspects of colorectal cancer: tumor depth (T), extent of involvement of lymph nodes (N), and metastasis (M).
- Tumor depth: The tumor depth ranges from T1 to T4, where T1 means that the tumor is very small and confined to the wall of the gut. T4 means that the tumor has involved neighboring organs.
- Lymph nodes: This ranges from N0, which means that no lymph nodes are involved, to N3, which means that a lymph node far away from the gut is involved.
- Metastasis: This includes M0, which means no metastasis, and M1, which means that the cancer has spread to distant organs.
Different T, N, and M combinations give rise to five stages of colon cancer. These are:
- Stage 0: This is the earliest stage of colorectal cancer. In this stage, the cancer does not go beyond its birthplace — the mucosa.
- Stage 1: In this stage, colon cancer may extend slightly beyond the mucosa but is limited to only the next major gut wall layer – the submucosa and has no lymph node involvement or evidence of metastasis.
- Stage 2: In this stage, the cancer grows further and involves deeper layers of the bowel wall or directly grow into adjacent organs but will not involve any lymph nodes.
- Stage 3: When colon cancer of any size involves a lymph node but has not spread to other distant organs, it is considered as stage 3.
- Stage 4: This is when the cancer has spread to other organs, such as the liver and lungs.
Based on location
The Surveillance, Epidemiology, and End Results (SEER) database classifies colon cancer stages differently than the TNM staging and stage groups. There are three SEER stages based on the location of the cancer:
- Localized: In the localized stage, colon cancer does not go beyond the colon.
- Regional: In the regional stage, the cancer extends beyond the colon but does not go too far. It may involve nearby organs or the lymph nodes.
- Distant: In the distant stage, colorectal cancer will go beyond the regional stage to involve distant organs such as the lungs, brain, and spine.
What are the survival rates for different colon cancer stages?
Generally speaking, the survival rate decreases as the stage of cancer increases because a higher stage indicates a more severe disease. The same is true for colon cancer.
Based on the SEER staging of colorectal cancer, the survival rates for different stages are as follows:
- Local: This is the least severe stage with a good prognosis. Up to 91% of such patients will live for the next five years.
- Regional: With this stage, up to 72% of patients will live for the next five years.
- Distant: This is the most advanced stage and only 13% of such patients are expected to live for the next five years.
How can the growth of colon cancer be diagnosed?
There are several tests that can detect the growth of colon cancer. In this section, we will look at the tests that can be used at each stage of growth beginning from the first cancerous mutations to full-blown colon cancer with metastasis.
Mutations that give rise to colorectal cancer are not routinely tested except in patients with a family history of colon cancer or are younger in age.
People who have a family history of genetic diseases like Lynch Syndrome and Familial Adenomatous Polyposis will likely be advised of genetic testing.
Testing for polyps is done in two groups of people:
- Those with genetic predisposition: As discussed above, these people undergo screening at an earlier age.
- Those without genetic predisposition: People without genetic mutations also have to undergo screening beginning at 45 years of age.
The following methods are used to diagnose polyps:
- Colonoscopy: A colonoscopy makes use of a flexible camera that is inserted into the gut so the doctor can directly look for polyps. It also allows the doctor to take biopsies (cut sections) from the polyp or remove it entirely.
- Sigmoidoscopy: Similar to a colonoscopy, a sigmoidoscopy uses a camera that is used to look for polyps. However, a sigmoidoscopy looks only at the last part of the gut — the sigmoid and rectum.
The only way to definitely diagnose colorectal cancer is to take out a piece of it and look at it under a microscope. This is what a biopsy means.
As discussed previously, colon cancer comes from polyps. Therefore, biopsies taken during a colonoscopy help determine whether a polyp is cancerous or not.
After a biopsy confirms colon cancer, the next step is to find out whether the cancer has spread or is limited to the colon. This is where imaging tests come in, such as:
- CT scan: A CT scan uses X-rays to generate images of the body. It can image the whole body and is commonly used to diagnose metastatic colorectal cancer.
- MRI: Similar to a CT scan, an MRI can also generate an image of the whole body. MRIs do not use X-rays and are therefore much safer than CT scans. But they are more expensive.
- PET scan: A PET scan will light up wherever cancer is present. This is because cancers have a higher metabolism compared to normal cells and a PET scan utilizes this feature to diagnose metastasis.
Can colorectal cancer develop within 1 year?
Yes, colorectal can develop within 1 year. If a polyp has been diagnosed at a later stage, it can quickly develop into cancer. However, it usually takes 5-15 years for colon cancer to develop from scratch.
Does colon cancer get worse quickly?
Although it’s possible for colon cancer to get worse quickly, it is rare because it is a slow-growing cancer.
How long can colorectal cancer go untreated?
Untreated colorectal cancer patients live a median of 24 months from diagnosis.
At what stage is colon cancer fatal?
When colon cancer spreads throughout the body, the prognosis is very poor and survival is very low. This is usually a stage 4 disease.
At what stage of colon cancer do symptoms appear?
Colorectal cancer symptoms usually appear in more advanced or larger cancers.