Colon cancer develops when tumorous growths form in the large intestine. It often produces no symptoms in the early stages, but people should see a doctor if they notice persistent changes in bowel habits.
The colon, or large intestine, is where the body draws out water and salt from solid waste. The waste then moves through the rectum and exits the body through the anus. Rectal cancer originates in the rectum, the final several inches of the large intestine, closest to the anus.
Colorectal cancer, which describes co-occurring colon cancer and rectal cancer, is common.
According to the
Healthcare professionals recommend regular colorectal cancer screenings for adults aged
In this article, we look at how to recognize and treat colon cancer, why it develops, and how to prevent it.
Symptoms and signs may include
- diarrhea or constipation
- changes in stool consistency, such as loose, narrow stools
- blood in the stool, which may make stools appear dark brown or black
- bright red bleeding from the rectum
- abdominal pain, cramping, bloating, or gas
- continual urges to defecate despite passing stools
- weakness and fatigue
- unexplained weight loss
- irritable bowel syndrome
- iron-deficiency anemia
Weight loss and abdominal pain usually occur in the later stages of the disease.
If cancer spreads to a new location in the body, such as the liver, it can cause additional symptoms, such as jaundice.
Colon cancer often causes no symptoms in the earliest stages, but symptoms may become more noticeable as the disease progresses. If people do have symptoms in the early stages, they may include:
- blood in the stool
- a change in frequency or type of bowel movements, such as diarrhea, constipation, or narrow, ribbon-like stools
- the feeling of not emptying the bowels after a bowel movement
- abdominal pain, cramping, or bloating
- nausea and vomiting
- anemia, due to intestinal bleeding
- loss of appetite
- fatigue and weakness
- unexplained weight loss
Symptoms in males
According to Brigham and Women’s Hospital, symptoms of colon cancer usually appear the same in males and females. Males may notice the symptoms listed above.
Symptoms in females
There are different ways of assigning a stage to cancer. The stages indicate how far cancer has spread and the size of any tumors.
In colon cancer, the stages develop
- Stage 0: Also known as carcinoma in situ, at this point, the cancer is in a very early stage. It has not grown farther than the inner layer of the colon and will usually be easy to treat.
- Stage 1: Cancer has grown into the next layer of tissue.
- Stage 2: Cancer has reached the outer layers of the colon but has not spread beyond the colon.
- Stage 3: Cancer has grown through the outer layers of the colon and reached one to three lymph nodes. It has not spread to distant sites.
- Stage 4: Cancer has reached other tissues beyond the wall of the colon. As stage 4 progresses, colon cancer reaches distant parts of the body.
Usually, cells follow an orderly process of growth, division, and death. Cancer can develop when cells grow and divide uncontrollably and do not die at the normal point in their life cycle.
According to the
Cancer happens as a result of changes in DNA within cells. Certain genes called oncogenes help cells stay alive, grow, and divide. Tumor suppressor genes help regulate cell division and cell death.
Changes to DNA can affect oncogenes and tumor suppressor genes, resulting in multiple gene changes that may lead to colon cancer.
Polyps are growths that form on the inside of the colon. Polyps are noncancerous, but cancer can begin with some types of polyps.
If a person has a type of noncancerous polyp called an adenomatous polyp, they have an
Cancerous cells may spread from malignant tumors to other parts of the body through the blood and lymph systems.
These cancer cells can grow and invade healthy tissue nearby and throughout the body in a process called metastasis. The result is a more serious, less treatable condition.
The exact causes of colon cancer are unknown, but there are several potential risk factors.
Adenomas may resemble the lining of a healthy colon but appear different under a microscope. They can become cancerous.
Colon cancer rarely develops from hyperplastic polyps, as they are typically benign.
Uncontrolled cell growth can occur following genetic damage or changes to DNA.
Around 5–10% of colon cancers result from specific hereditary conditions that increase the risk of polyps, colon cancer, and potentially other cancers in some members of the family.
Several inherited conditions also
- attenuated familial adenomatous polyposis
- familial adenomatous polyposis (FAP)
- Gardner syndrome, which is a different type of FAP
- Lynch syndrome, or hereditary nonpolyposis colorectal cancer
- juvenile polyposis syndrome
- Muir–Torre syndrome, which is a variant of Lynch syndrome
- MUTYH-associated polyposis
- Peutz–Jeghers syndrome
- Turcot syndrome, another variant of FAP
It is possible to have these genetic features without developing cancer.
Traits, habits, and diet
Age is a significant risk factor for colon cancer. Around 90% of people who receive a diagnosis of colorectal cancer are over 50 years of age. However, it is becoming more common in people under 50.
As the colon is part of the digestive system, diet and nutrition play central roles in its development.
Low fiber diets can contribute. Also, according to one
Some conditions and treatments have links to an increased risk of colon cancer. These include:
- a medical history of polyps
- inflammatory bowel diseases, such as ulcerative colitis or Crohn’s disease
- other cancers, such as breast, ovarian, or endometrial
- obesity or being overweight
Other risk factors
Other risk factors for colon cancer
- having a parent, sibling, or child with a history of colon or rectal cancer
- a personal history of colon, rectal, or ovarian cancer
- a personal history of polyps 1 centimeter or more in size, or with abnormal cells
- inherited genetic conditions, such as Lynch syndrome
- having chronic ulcerative colitis or Crohn’s disease for 8 years or longer
- regularly consuming alcohol three or more times a day
- smoking cigarettes
- older age
- lack of physical activity
- low fiber, high fat diets lacking in fruit and vegetables
- race and ethnicity, as African Americans, Asians, and people of Hispanic descent may receive a colon cancer diagnosis at a later stage of the disease
Treatment will depend on the type and stage of colon cancer. A doctor will also consider a person’s age, overall health, and certain other characteristics when deciding on the best treatment option.
The aim of treatment will be to remove the cancer, prevent its spread, and reduce any uncomfortable symptoms.
The main treatment for early stage colon cancer is
Surgery to remove part or all of the colon is a colectomy. During this procedure, a surgeon will remove the part of the colon that contains cancer, as well as some of the surrounding area.
A surgeon may remove nearby lymph nodes to reduce the risk of spreading. The surgeon will then either reattach the healthy portion of the colon or create a stoma, depending on the extent of the colectomy.
A stoma is a surgical opening in the wall of the abdomen. Through this opening, waste passes into a bag, which removes the need for the lower part of the colon. This is a colostomy.
Other types of surgery include:
- Endoscopy: A surgeon may be able to remove some small, localized cancers using this procedure. They will insert a thin, flexible tube with a light and camera attached. It will also have an attachment for removing cancerous tissue.
- Laparoscopic surgery: A surgeon will make several small incisions in the abdomen. This may be an option to remove larger polyps.
- Palliative surgery: The aim of this type of surgery is to relieve symptoms in cases of untreatable or advanced cancers. A surgeon will attempt to relieve any blockage of the colon and manage pain, bleeding, and other symptoms.
During chemotherapy, a cancer care team will administer medications that interfere with the cell division process. They achieve this by disrupting proteins or DNA to damage and kill cancer cells.
These treatments target any rapidly dividing cells, including healthy ones. These can usually recover from any chemotherapy-induced damage, but cancer cells cannot. The medicines travel through the whole body, and the treatment will take place in cycles, so the body has time to heal between doses.
A cancer specialist, or oncologist,
- before surgery to shrink a tumor to make it easier to remove
- after surgery to kill any remaining cancer cells
- if cancer has spread to other organs
Side effects of chemotherapy may include:
- hair loss
Combination therapies often use multiple types of chemotherapy or combine chemotherapy with other treatments.
Radiation therapy kills cancer cells by focusing high energy gamma rays on them. A cancer care team may use external radiation therapy, which expels these rays from a machine outside of the body.
With internal radiation, a doctor will implant radioactive materials near the cancer site in the form of a seed.
Some metals, such as radium, emit gamma rays. The radiation may also come from high energy X-rays. A doctor may request radiation therapy as a standalone treatment to shrink a tumor or destroy cancer cells. It can also be effective alongside other cancer treatments.
For colon cancer, cancer care teams tend not to administer radiation treatments until the
Side effects of radiation treatment may include:
- mild skin changes that resemble sunburn or suntan
- appetite loss
- weight loss
Most side effects will resolve or subside a few weeks after completing treatment.
A physician will carry out a complete physical examination and ask about personal and family medical histories.
They may also use the following diagnostic techniques to identify and stage cancer:
During a colonoscopy, a doctor will insert a long, flexible tube with a camera on one end into the rectum to inspect the inside of the colon.
A person may have to follow a special diet before the procedure, such as a clear liquid diet
If the doctor finds polyps in the colon, a surgeon will remove them and send them for biopsy. In a biopsy, a pathologist examines the polyps under a microscope to look for cancerous or precancerous cells.
A similar procedure, called a flexible sigmoidoscopy, allows a doctor to examine a smaller portion of the colorectal area. This method does not reach as far as a colonoscopy. Also, a full colonoscopy may not be necessary if a sigmoidoscopy does not reveal polyps or if they are only within a small area.
Double-contrast barium enema
This X-ray procedure uses a liquid called barium to provide clearer images of the colon than a standard X-ray. A person may need to avoid eating or drinking before undergoing a barium X-ray.
A doctor will inject a liquid solution containing the element barium into the colon through the rectum. They follow this with a brief pumping of air to smooth over the barium layer to provide the most accurate results.
A radiologist will then conduct an X-ray of the colon and rectum. The barium appears white on the X-ray, and any tumors and polyps will appear as dark outlines.
Following diagnosis, a doctor will determine the stage of the cancer based on the size and extent of the tumor and the spread to nearby lymph nodes and distant organs.
The stage of a person’s cancer will determine their treatment options and inform their outlook.
There is no guaranteed way to prevent colon cancer. However, some preventive measures
- maintaining a moderate weight
- exercising regularly
- consuming plenty of fruits, vegetables, and whole grains
- limiting the intake of saturated fats and red meat
People should also consider limiting their alcohol consumption and quitting smoking.
Symptoms may not appear until cancer has progressed. For this reason, the American College of Physicians recommends screening for people aged 50–75 years, including fecal testing once every 2 years, a colonoscopy every 10 years, or a sigmoidoscopy every 10 years plus fecal testing every 2 years.
The regularity of screening depends on an individual’s level of risk. People can consult their doctor for personal recommendations.
- localized: 91%
- regional: 72%
- distant: 14%
- all stages combined: 63%
However, these survival rates are from 2010–2016, and treatment and research are continually advancing. Early detection and treatment are the most effective ways to improve the outlook of a person with colon cancer.
The survival rate refers to the proportion of people who are still alive for a length of time after receiving a particular diagnosis. For example, a 5-year survival rate of 50% means that 50% of people, or half, are still alive 5 years after receiving the diagnosis.
It is important to remember that these figures are estimates and based on the results of previous studies or treatments. A person can consult a healthcare professional about how their condition is going to affect them.
Colon cancer is a type of colorectal cancer. It means that there is a cancerous growth in the colon.
Signs of colon cancer may not be obvious in its earlier stages. However, they may include pain, rectal bleeding, or blood in the stool.
There are many treatment options for colorectal cancer. These include chemotherapy, radiation therapy, and surgery.