What Is Colon Cancer? Symptoms, Diagnosis and Treatments

Colon cancer – sometimes also known as colorectal cancer – occurs when cells inside the part of the large intestine begin to grow and divide abnormally.

The colon is where the body absorbs water, salt, and nutrients from partially digested food.

The food gradually moves down through the colon and is expelled from the rectum as a bowel movement.

Although you can have either colon or rectal cancer, the two often occur together.

The third most common cause of death in the US, colon cancer is diagnosed in more than 90,000 people each year.

Cellular Metabolism

Healthy cells grow, die, and are replaced by the body; cancer cells, however, grow and multiply but don’t die.

All cancers are the result of uncontrolled cell growth and colon cancer is no exception.

In most cases, colon cancer begins as a small, noncancerous growth on the inner walls of the intestine.

Called adenomatous polyps, these are initially benign tumors.

These polyps cannot be seen except with a special test called a colonoscopy and rarely produce any symptoms.

Over time, however, the tissues become malignant (cancerous).

Two other types of polyps found in the colon include hyperplastic polyps, which rarely become cancerous, and inflammatory polyps.

Inflammatory polyps usually occur because the colon has been inflamed by a condition like colitis.

They may become cancerous.


Once a tumor develops, the colon cancer cells will begin to invade healthy tissue, causing serious destruction.

As the tumors spread and become larger, they may travel through the lymphatic system or blood and spread to other parts of the body – a process called metastasis.

Colon cancer that has metastasized is much more difficult to treat.

Types of Colon Cancer

Colon cancer can take one of several different forms.

All but one type are relatively rare and none account for more than one percent of colon cancer cases.

Almost all types of colon cancers are slow-growing.

The different forms of colon cancer include adenocarcinomas, carcinoid tumors, gastrointestinal stromal tumors, leiomyosarcomas, melanomas, and primary colorectal lymphomas.

  • Adenocarcinomas are the most common type of colon cancer; the tumor forms in the epithelial cells lining the colon. Around 95 percent of all colon cancers begin as adenocarcinomas.
  • Carcinoid tumors occur in tissue that produces hormones, such as the pancreas, testes, or ovaries.
  • Gastrointestinal stromal tumors (GISTs) can be found in any area of the gastrointestinal tract. They start in special nerve cells known as the interstitial cells of Cajal.
  • Leiomyosarcomas are tumors that occur in soft tissues like muscles, fat or blood vessels.
  • Melanomas are cancers in the skin cells. When colon cancer is caused by melanoma, it is because the cancer cells have metastasized from somewhere else in the body.
  • Lymphoma – also called lymphatic cancer – is a type of cancer that affects the immune system. Primary colorectal lymphomas are lymphomas that begin in the colon itself, as opposed to spreading there from somewhere else.


Risk Factors

Like all cancers, many factors influence the risk of colon cancer.

In most cases, colon cancer is probably not the result of a single cause, but of several factors working in concert.

Genetics, lifestyle habits, diet, inflammatory bowel conditions, radiation, and endocrine disorders like diabetes increase the risk of colon cancer.

  • Genetics

A family history of colon cancer increases an individual’s risk of developing the disease.

Some kinds of colorectal cancer are called hereditary or inherited because several generations in a family have a history of the disease.

Genetic mutations are transmitted to succeeding generations.

Nonpolyposis colorectal cancer and familial adenomatous polyposis are the two most common kinds of inherited colorectal cancer.

A child of a parent who carries this gene has a 50 percent chance of inheriting the gene.

About 5 percent of colorectal cancer is caused by one of these two inherited cancer syndromes.

Ashkenazi Jews are one group at higher risk of these types of cancers, as about six percent of the population carries a mutated gene.

Random genetic mutations may increase the risk of colon cancer.

  • Lifestyle

The Western diet, which is typically low in fiber and high in red meat and fat, may increase the risk of colon cancer, especially in those who have a family history of the disease.

Being obese and having a sedentary lifestyle may also increase colon cancer risk.

The use of tobacco in any form and heavy alcohol consumption also increases the risk of colon cancer.

Tobacco affects overall circulation and also has a direct effect on body cells, while excessive alcohol consumption is very irritating to the gastrointestinal tract and damages the liver.

  • Inflammatory Bowel Conditions

Inflammatory bowel diseases include Crohn’s disease and ulcerative colitis.

Crohn’s disease can cause inflammation in any part of the gastrointestinal tract, while ulcerative colitis causes inflammation specifically in the lining of the colon or large intestine.

The longer you have either condition, the higher your risk for colon cancer; risk starts to increase about eight to 10 years after the inflammatory conditions first develop.

The greater the involvement in the colon, the higher the risk.

If the inflammation is confined to the rectum, the risk of colon cancer is not as high.

A rare complication of inflammatory bowel disease called primary sclerosing cholangitis results in inflammation of the drainage ducts for the liver.

Primary sclerosing cholangitis also increases colon cancer risk.

  • Radiation

Radiation comes in two forms – the sort from environmental conditions, primarily sunlight – and direct radiation from X-rays use to diagnose and treat certain medical conditions.

Radiation of the abdomen may increase the risk of colorectal cancers.

This may occur because the radiation spurs or activates genetic mutations.

  • Endocrine Disorders

Endocrine glands contain special hormone-manufacturing tissue and secrete these hormones directly into the bloodstream.

The thyroid and pancreas are probably two of the best-known endocrine glands.

When the pancreas malfunctions, diabetes develops because the blood sugar is not properly regulated.

Diabetes is one endocrine disorder that increases the risk of colon cancer.

  • Other Factors

Age is a colon cancer risk factor; nearly all colon cancer diagnoses are made in people over the age of 50.

People of African American descent have a higher risk of colon cancer than Caucasians, Asians, or Hispanics.



At the time of this writing, the recommendations for colon cancer screening include both men and women age 50 or older.

All adults should begin screening at age 50; the gold standard for screening is a colonoscopy.

People who are low risk and who don’t have a family history of colon cancer can usually be screened every 10 years.

Those who are at higher risk because of family history or a history of precancerous polyps are often advised to have a colonoscopy every five to 10 years.

Screening methods include lab tests for blood and stool, optical colonoscopy, and diagnostic imaging studies.

  • Lab Screening Tests

There are several screening tests for colon cancer.

The first is a high-sensitivity fecal occult blood test, which looks for signs of blood in the stool.

Two types – the guaiac and the fecal immunochemical (or immunohistochemical) are used.

If this is the only screening test used, it should be performed annually, using multiple stool specimens.

Even if the test is positive, this does not necessarily indicate colon cancer, as other conditions like hemorrhoids and inflammatory bowel disease may cause bleeding.

The stool DNA test looks for DNA biomarkers and genes typically found in colon cancer and precancerous adenomas.

This test should also be confirmed by colonoscopy if positive.

  • Sigmoidoscopy

This test involves inserting a lighted tube into the patient’s rectum.

The colon can be visualized during the test and polyps biopsied or tissue specimens obtained during the procedure.

The procedure should be performed every five years for most patients.

  • Optical Colonoscopy

Similar to the sigmoidoscopy, this test also uses a flexible tube inserted into the rectum.

Because it is longer, doctors can remove growths that cannot be reached during sigmoidoscopy.

Screening with a colonoscopy is usually recommended every 10 years in healthy patients.

Optical colonoscopy is considered the gold standard in colon cancer screening tests.

Intravenous sedation is required for the procedure; the colon must be thoroughly cleaned ahead of time.

  • Virtual Colonoscopy

This non-invasive test does not require sedation, although the colon must still be thoroughly cleaned prior to the procedure.

Special X-ray equipment is used to create pictures of the colon; these can show polyps, tumors, and other abnormalities.

Medicare and some insurance companies do not pay for virtual colonoscopy, and if growths are found, they must be removed during an optical colonoscopy.

  • Other Methods

A double-contrast barium enema uses barium to show images inside the colon.

This method is not as sensitive as other screening and is not generally recommended unless the patient cannot have a sigmoidoscopy or colonoscopy.

A single fecal occult blood test can show blood in the stool but is not used to screen for colon cancer.

Other diagnostic imaging tests include CAT scans, MRIs, and ultrasounds, which are typically used to look for metastases.



The initial symptoms of colon cancer are often very subtle; by the time obvious symptoms appear, the tumor is often fairly well advanced.

Common signs of colon cancer include changes in bowel habits, changes in the stool itself, bleeding and/or anemia, gastrointestinal distress, unexplained weight loss, and fatigue.

Although pain is a symptom of colon cancer, it is often a late-stage symptom and may indicate cancer has spread.

Many of these symptoms accompany inflammatory bowel diseases as well, which can complicate the ability to diagnose colon cancer.

If these symptoms persist for more than a few weeks, it is important to consult a medical professional.

  • Bowel Habits

While a certain amount of variation in bowel habits is normal, dramatic changes or obvious changes that occur and then persist may be an early symptom of colon cancer.

For example, people who are chronically constipated may develop persistent diarrhea and vice versa.

  • Changes in the Stool

Changes in stool consistency – from hard to soft, for example – may be a sign of colon cancer.

Changes in the amount of color may also be early warning signs.

Sometimes the diameter of the stool will change, becoming much narrower than was previously the case.

  • Bleeding and/or Anemia

Signs of rectal bleeding include dark stools, stools with blood in them, or bright red blood on the toilet paper.

If the bleeding becomes chronic, anemia (low red blood cell count) may develop.

  • Gastrointestinal Distress

Almost any kind of gastrointestinal distress may be a symptom of colon cancer.

These can range from nausea or heartburn to vomiting.

Some patients complain of bloating, excessive gas, or cramps, which may cause abdominal discomfort or outright pain.

  • Weight Loss

Unexplained weight loss is a common symptom of all cancers, not just colon cancer.

Cancer cells divert nutrients from other cells, which causes weight loss even in patients who seem to be eating a normal diet and who are not trying to lose weight.

  • Fatigue

Just as cancer cells divert nutrients, they also sap the body’s energy.

Weakness, fatigue, and lethargy are all possible colon cancer symptoms.

The symptoms are chronic, often severe, and not relieved with rest or sleep.

  • Other Symptoms

A continual urge to have a bowel movement may be another symptom of colon cancer.

It may result from increasing tumor size that causes pressure inside the colon.

Once the tumor becomes large enough to metastasize, other symptoms may develop.

For example, the liver is the most commonplace for colon cancer metastases, and patients may develop pain in the upper abdomen or become jaundiced (yellow skin).


Diagnosis and Stages

Sometimes colon cancer is diagnosed after a screening test reveals a possible problem, while other patients go to the doctor because they have developed symptoms that cause concern.

The diagnosis of colon cancer begins with a review of the patient’s symptoms.

A physical examination, review of family and patient medical history, lab and diagnostic tests are also included.

The stage at which colon cancer is diagnosed is also important.

  • Symptom Review

In addition to symptoms specifically related to possible colon cancer, patients often present with other symptoms that must be considered.

For example, a patient might report insomnia or shortness of breath, neither of which may have anything to do with colon cancer.

Still, these symptoms must be considered, as they may also need to be dealt with or may indicate one or more other conditions besides colon cancer.

It’s also important to evaluate symptoms that may pose a risk of complications if a patient needs surgery, such as chronic anemia.

  • Physical Examination

The physical examination will focus on the abdomen, but usually encompasses other areas of the body, such as the heart and lungs.

Physical data also includes vital signs (blood pressure, temperature, and respiration).

A check of the mucous membranes may indicate anemia.

The physician will usually palpate (feel) the abdomen and the lymph glands as well as the area over the kidneys.

  • Medical and Family History

Among the aspects of the medical history, the physician will note are any previous history of cancer or inflammatory bowel disease in the patient or family, the surgical history, and any history of conditions that may make treatment more difficult, such as heart disease or diabetes.

  • Lab Tests

Lab tests fall into two major groups: general lab tests that reflect overall health or specific aspects of health, and tests that are more specific to cancer of the colon.

Common general lab tests include a complete blood count (CBC) to evaluate the size, shape, and the number of the various kinds of blood cells, a chemistry screening panel, which assesses electrolytes like sodium and potassium, liver function tests, and a urinalysis.

The carcinoembryonic antigen (CEA) is a blood test that can indicate the stage of the disease – a higher level indicates a higher stage.

Genetic testing is used to identify specific gene mutations and guide treatment.

Microsatellite instability (MSI) is another genetic test used to guide treatment, as tumors with MSI don’t respond to certain chemotherapy drugs.

  • Diagnostic Tests

A colonoscopy is nearly always indicated when colon cancer is suspected.

Occasionally a sigmoidoscopy will be used if the patient cannot tolerate colonoscopy or there is a high risk of complications.

During the procedure, the doctor will take a tissue sample to analyze for colon cancer.

A CT scan or ultrasound can also be used to help obtain tissue for a needle biopsy if there is some reason not to perform a colonoscopy.

  • Staging

The purpose of staging is to determine how far cancer has progressed, which will help direct treatment.

The letters T, N, and M are used for staging.

T indicates how large the tumor is and whether it has invaded the intestinal wall.

N indicates whether the tumor has spread to nearby lymph nodes and M indicates if the tumor has metastasized to other organs.

These three indicators are used to classify colon cancer as stage O, I, II, III, or IV, with IV being most serious.


Treatments and Drugs

All cancer treatment is dependent on factors such as the type of tumor, how much it has spread, the patient’s age, general condition, and other factors.

Colon cancer treatment falls into three main categories: surgery, chemotherapy, and radiation therapy.

In many cases, these may be administered consecutively.

Although not used for direct colon cancer treatment, many medications may also be used in colon cancer, such as pain medications, stool softeners, and antibiotics.

  • Surgery

Surgical removal of colon cancer is often the first treatment step even when other treatments will also be used.

The surgeon performs a colectomy or removal of all or part of the colon.

In addition to removing the tumor itself, the surgeon removes adjacent areas of the colon, to ensure that all tumor cells are removed.

Nearby lymph nodes are typically removed when the colectomy is performed, as the risk that they also contain small tumors is considered high.

Once the diseased colon has been removed, the surgeon may reattach the colon to the rectum.

In some cases, the surgeon may need to create a colostomy by bringing the end of the colon out through the skin of the abdomen.

In that case, the patient must wear a bag to collect stool.

If the colon cancers are small and/or localized, the surgeon may be able to remove them through small incisions using a flexible lighted camera called a laparoscope.

Sometimes the surgery is not intended to cure cancer.

If the tumor is very large, for example, surgery may be used to debulk the tumor (make it smaller), resolve an intestinal blockage, or correct problems like intestinal bleeding.

  • Chemotherapy

Chemotherapy is the use of chemicals that damage and kill cancer cells by interfering with their ability to divide.

The drugs also affect normal cells, but the normal cells are usually able to recover and heal, while cancer cells can’t recover.

Chemotherapy is usually administered intravenously and is typically used to treat cancer that has metastasized.

Unlike radiation and surgery, chemotherapy drugs affect cells throughout the body.

Chemotherapy has numerous side effects, such as hair loss and fatigue.

It also often causes nausea, vomiting, and loss of appetite, which can lead to weight loss.

A variety of different drugs are used in chemotherapy; the exact drug or combination of drugs is dependent on factors such as the type of tumor and other considerations.

  • Radiation

Radiotherapy or radiation treatment is the use of X-rays to kill cancer cells.

The high-energy rays damage the molecules in the cancer cells and kill the cells.

Gamma rays from materials like radium are used in radiotherapy.

The treatment may be used to shrink a tumor prior to surgery, as a stand-alone treatment, or in combination with other methods.

Radiotherapy is more likely to be used for advanced cancers or cancers that have penetrated the rectal wall or spread to nearby lymph nodes.

Like other treatments, radiation may cause side effects, including skin irritation and damage, vomiting, diarrhea, fatigue, and weight loss.


Coping and Support

The diagnosis of colon cancer can be devastating and raises many questions about the disease itself, treatment, finances, and other complex issues.

In order to cope with the disease, most patients need information about colon cancer as well as resources such as support groups or financial aid.

  • Information

Many resources offer specific information about colon care, its treatment, and prognosis.

Most medical professionals have patient education and information resources in the office or can direct the patient and family to online resources.

The federal government has extensive information about all types of cancer on the National Cancer Institute website, Cancer.gov.

Other resources include the American Cancer Society and those of medical institutions like the Mayo Clinic.

  • Finances

Cancer diagnosis and treatment don’t come cheap.

Medicare and other insurances typically pay a percentage of the costs, so patients will have out-of-pocket expenses.

A variety of organizations provide help with medical billing, reimbursement, and insurance coverage issues.

The Cancer Financial Assistance Coalition and the Partnership for Prescription Assistance are good places to start.

Most pharmaceutical companies also offer programs to cover the costs of medications if the patient meets certain financial criteria.

Social Security, Medicaid, state disability programs, and local resources may offer other options.

If the patient must travel for treatment, a number of organizations provide temporary housing assistance and many major treatment centers also have hospitality houses or arrangements with local motels.

  • Emotional Support

Both patients and family members need emotional support.

National, state, and local associations offer support programs and many localities have cancer survivors or support groups.

Caregivers may need respite care if the patient reaches a terminal stage.

Neighbors and friends may also be sources of emotional support and in some cases can help with caregiving duties or transportation.


Colon Cancer Prevention

There are of course no guarantees that prevention strategies will be effective when it comes to colon cancer, but there is some evidence that certain lifestyle strategies may help.

Even when colon cancer can’t be prevented, early detection and treatment can be life-saving.

Many of the basic strategies for colon cancer prevention are those that promote overall health as well, such as eating a healthy diet, getting regular exercise, not smoking, and limiting alcohol consumption.

  • Diet and Colon Cancer

Of all the possible strategies to prevent colon cancer, diet probably has the biggest impact.

There are several reasons for this. First, there is some evidence that a diet high in red meat and saturated fat increases the risk of colon cancer.

Scientists are not sure if it is those two factors alone or the fact that they tend to decrease the intake of fiber-rich foods such as fruits, whole grains, and vegetables.

The typical Western diet is high in fat and low in fiber.

People who move from other areas where the reverse is true and begin to eat the American diet are at greater risk of colon cancer than those who continue to eat their traditional diets.

Researchers have speculated that the dietary change affects beneficial bacteria in the colon or causes inflammation in the bowel.

Second, a diet high in fruits and vegetables has a protective effect, partly because the high fiber content of these foods promotes a healthy balance of bacteria in the intestine and colon.

Fruits and vegetables are also rich in vitamins, antioxidants, and phytochemicals (chemicals from plants), which promote cellular health.

Third, a healthy diet helps prevent weight gain and obesity; both increase colon cancer risk.

  • Vitamins, Minerals, Medications, and Supplements

The use of vitamins and supplements to prevent cancer is known as chemoprevention.

Research is limited or inconsistent in many cases, partly because it is very difficult to identify the effect of a specific vitamin or supplement in a condition such as colon cancer that develops over a long period of time.

However, the following may have a protective effect:

  • Antioxidants defend the body from damage caused by unstable molecules called free radicals. Animal testing indicates antioxidants may help prevent cancer. These include beta-carotene, lycopene, and various vitamins including vitamins A, C, and E.
  • Aspirin may help in colon cancer prevention, according to some studies. This may be related to its anti-inflammatory role in the body. However, aspirin can also be irritating to the gastrointestinal tract when taken over a long period and may have other side effects.
  • Calcium may be linked to colon cancer prevention when taken with vitamin D. Calcium seems to decrease the risk and prevalence of precancerous polyps.
  • Curcumin, found in the spice turmeric, has anti-inflammatory properties and remains in the gut rather than being absorbed into the bloodstream. Commonly used in Indian foods such as curries, curcumin may also have anti-tumor properties.
  • Raw garlic is antibacterial, may be able to prevent cancer-producing substances from forming, and may also increase DNA repair.
  • Other substances that may play a role in colon cancer prevention include folic acid, Omega-3 fatty acids, yeast with selenium, soy products, statin medications, and vitamin D.


  • Exercise

Exercise promotes health by increasing circulation to the cells and also helps people lose weight or maintain weight loss.

Physical activity promotes the process of digestion and helps reduce constipation.

It may also promote immune system function and reduce inflammation.

There is also evidence that exercise improves colorectal cancer survival rates.

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