Colorectal cancers (CRC) are the second most common cause of cancer-related deaths in the United States. In 2023 alone, around 153,000 people were expected to be diagnosed with this cancer.
However, if you consider the anatomy of the colon, CRC is two types of cancer: colon and rectal. But why are they always talked about together? Better yet, what are the differences between them?
Let’s find out.
Why is it called colorectal cancer?
Colorectal cancer is a term used to describe cancers that develop from colorectal polyps (cancerous growths) in the colon or rectum. These can also be known as rectal or colon cancer, depending on where they start.
However, they’re often grouped because they have similar symptoms, signs of spread, and treatments.
What are rectal and colon cancer?
Rectal cancer occurs when cancer cells form in the rectal tissue — the last 12 – 15 cm of the large intestine that connect to the anus. It includes adenocarcinomas (98%), lymphomas (1.3%), carcinoid tumors (0.4%), and sarcomas (0.3%).
This type of cancer begins when cells in the rectal walls experience DNA mutations. While it isn’t clear what exactly causes these mutations, inherited genes, age, race, obesity, and smoking play a significant role in their development.
In contrast, colon cancer affects the large intestine, excluding the last 12 – 15 cm that make up the rectum. It affects the colon tissue, has 0 to 4 stages, and may also be caused by inherited genetic mutations.
What is the difference between colon and rectal cancer?
As we’ve established, while colon and rectal cancers have common features, they aren’t the same entity. Let’s understand what makes them different from each other.
1. Location
Colon cancers affect your colon, a five-foot section of the large intestine. In contrast, rectal cancer affects only the last six inches of your colon (known as the rectum), which extends from the sigmoid colon to the anus.
2. Causes
Genetic factors, diet, and digestive tract disorders contribute to the development of both types of cancer, and there is not much (or any) difference between their pathways of development.
For instance, a mutation of the APC gene is associated with a 100% risk of developing both colon and rectal cancer by age 40.
Similarly, a low intake of fiber, fruits, and vegetables is associated with a high risk of developing both colon and rectal cancer.
3. Recurrence
People who have had curative rectal tumor surgery are 22.5% more likely to experience a recurrence within five years. In a study of 188 patients operated for rectal tumors, 53 experienced cancer recurrence.
The recurrence rate was 50.9% for tumors of the lower rectum, 30% for tumors of the middle rectum, and 17% for tumors of the upper rectum, with the most common symptom being pelvic pain.
In contrast, people who’ve had surgery for colon cancer are 30 to 40% more likely to experience a recurrence within two to three years after treatment. For instance, in a study of 446 patients treated for colon cancer, almost 17% developed recurrent disease.
This means that colon cancer may have a higher rate of recurrence and may recur within a shorter period after surgery.
4. Survival
The median recurrence-free survival rate for people who’ve undergone rectal tumor surgery is 54 months (4.5 years) with a recurrence rate of 44.6% at five years and 58.4% at ten years.
In contrast, the average survival rates for people who’ve undergone colon cancer surgery are roughly 10% for distant metastatic recurrence, 70% for regional recurrence, and 90% for localized recurrence.
5. Mortality
Mortality caused by colon and rectal cancer differs according to cancer stage. However, people with stage IIB colon cancer have lower mortality rates than those with rectal cancer (by at least four months).
In contrast, rectal cancer patients at stages IIIC and IV have better survival rates compared to people with colon cancer by at least three months.
Both cancers are staged according to their spread to other structures, such as lymph nodes and nearby organs.
What are the symptoms of rectal and colon cancer?
While many rectal cancers have no symptoms, there are some signs clinicians may look for to confirm their diagnosis. These include the following:
- Bleeding (60%), such as bright red or dark maroon blood in stools
- Changes in bowel habits (43%), such as constipation, diarrhea, not feeling empty, narrow stools, or frequent bowel movements
- Occult bleeding (26%), which is bleeding that you can’t see with the naked eye
- Lower back and pelvic pain (5%)
- Weakness or fatigue (9%)
- Jaundice (<1%)
- Inability to hold back stools
- Flatulence
These symptoms can also be experienced by people with colon cancer. However, they can also experience the following symptoms not usually seen with rectal cancer:
- Abdominal pain
- Intestinal obstruction
- Iron-deficiency anemia
- Fatigue
What are the risk factors of rectal and colon cancer?
While the exact causes of colon and rectal cancer are unknown, several risk factors contribute to their development. Let’s take a look.
1. Hereditary factors
If a person develops colon or rectal cancer, their children have a 2.42 times higher chance of developing colon cancer, a 1.89 times chance of getting rectal cancer, and a 4.25 times chance if another family member is affected.
The risk increases to 3.87 times if the patient is younger than 40 years when diagnosed.
2. Genetic factors
Current research shows that genetic factors greatly influence the development of colon and rectal cancer.
For instance, people with hereditary nonpolyposis colon cancer syndrome (HNPCC) have a 40% risk of developing colon or rectal cancer during their lifetime. They may also be more susceptible to endometrial or urothelial cancer.
Similarly, people with a mutated APC gene may be at a 100% higher risk of developing familial adenomatous polyposis (FAP) before the age of 40. It can cause the development of hundreds of intestinal polyps and bone/brain tumors, which may put people at a higher risk of mortality.
3. Diet
Several studies have linked dietary factors with an increased risk of colon and rectal cancer.
For instance, a 2018 cohort study looking at 121,050 people for 26 years found that a high intake of red and processed meat was associated with a significant risk of developing colon cancer.
Another study found that an increased intake of high-fiber fruits and vegetables was associated with a reduced risk of colon and rectal cancer. Moreover, a high yogurt intake was also shown to lower the risk of developing these cancers.
4. Obesity
A higher body mass index (BMI) has been associated with an increased risk of colon and rectal cancer for men. According to a 2013 study, obesity (BMI higher than ≥ 30) leads to a 30–70% increased risk of colon cancer in men.
Obesity is also associated with worse colon cancer outcomes, such as high mortality and primary cancer recurrence. This is because it causes low-grade chronic inflammation, which can create a tumor microenvironment that enables cancer to flourish.
5. Alcohol consumption
Drinking too much can lead to an increased risk of developing colon cancer. However, this only affects people who drink ≥ 30 g/d per day.
Moreover, frequent drinkers have a 2.8 times higher chance of getting colon cancer compared to non-drinkers at 1.8 times.
6. Inflammatory bowel disease
Inflammatory bowel diseases, such as ulcerative colitis (UC) or Crohn’s disease, that affect the colorectal area can increase the risk of both colon and rectal cancers. This is because IBD causes oxidative damage to the DNA in the colon tissue, which may disable tumor-suppressing genes and enable tumor development.
In fact, people with UC have a 2% risk of developing colon cancer ten years after diagnosis. This number rises to 8% after 20 years, 18% after 30 years, and 30% after 40 years of disease duration.
Moreover, among people with IBDs, the overall risk of developing rectal cancer is 1% after ten years, 2% after 30 years, and 5% after 20 years from diagnosis.
7. High-fructose corn syrup consumption
Consuming products with high-fructose corn syrup (HFCS) may lead to a higher risk of colon cancer.
According to a 2022 study, the consumption of HFCS-sweetened beverages led to a 1.18 times/serving increase in the incidence of colon cancer. It also caused a higher risk of colon cancer mortality.
Another 2020 study showed that consuming beverages sweetened with HFCS could cause the rapid development of polyps into advanced and aggressive tumors that contained fructose, which facilitated their growth.
Final thoughts: are rectal and colon cancer truly similar?
Since colon cancer and rectal cancer both affect the large intestine, have similar symptoms, and require similar treatments, they’re often combined. But the thing to understand here is that these cancers affect two anatomically different areas of the gut — colon and rectum.
Plus, the risk factors for one type of cancer might not contribute to another. For instance, obesity, red meat consumption, and alcohol intake aren’t the top risk factors for rectal cancer. But they do increase the risk of getting colon cancer.
If you’ve hit 45 years of age, make sure to undergo colorectal cancer screening (via colonoscopy) to make sure your bowels are healthy!
