Understanding The Types Of Colon Cancer

The large intestine in the digestive system consists of two sections - the colon and rectum. Water and nutrient absorption occur in the first section of the large intestine (colon), and later the solid waste settles in the last part (rectum) until it leaves the body through the anus.

When you hear of colon or colorectal cancer, it is when the cells in the colon and rectum lining grow uncontrollably and abnormally. This cancer may start in any of the two sections, but the majority begin in the colon as silent tumors. These tumors may grow slowly without any noticeable symptoms until they are large.

Common types of colon cancer

The colon and rectum walls consist of multiple layers of tissue. Colon cancer develops in the interior layer (mucosa) and can spread outward to some or all the other layers.

Read on to learn more about the different types of colon cancer, their symptoms, and treatment options.

1. Adenocarcinoma

This is the most common type of colon cancer. It starts in epithelial cells, which line the colon surface, or at the end of the colon.

Adenocarcinomas have subtypes, including mucinous carcinoma that accounts for 10-15% of all colorectal adenocarcinomas. Another subtype is signet ring cell adenocarcinoma that accounts for less than 1% of all colorectal cancers.

Mucinous adenocarcinoma consists largely of mucus that facilitates the spread of cancer cells, thus making it more aggressive than other adenocarcinomas. However, signet ring cell adenocarcinoma, named so due to its appearance under a microscope, is often aggressive, presents late, and is more challenging to treat. Medullary adenocarcinomas have a more favorable prognosis.

Symptoms

• Blood in stool 

• Thin stools 

• Unexplained weight loss 

• Painful and tender abdomen 

• Changes in bowel habits

Colon cancer screening is critical to detect cancer even before the onset of any symptoms.  Adults should begin their screening at 45 years of age, according to the American Cancer Society¹ (ACS) and the U.S. Preventive Services Task Force². The diagnosis starts with a colonoscopy which allows doctors to see inside the colon and rectum.

Other tests follow if signs of colon cancer are discovered. Sometimes a biopsy may be necessary. This involves the removal of a small piece of tissue that is suspected to be cancerous and analyzing it in the lab for the presence of cancer. After colonoscopy and biopsy confirmation, blood tests and imaging tests such as C.T. scans and MRI scans³ can help the doctors know more about any spread.

Treatment

• Surgery

• Radiation therapy    

• Chemotherapy    

• Targeted therapy

2. Gastrointestinal neuroendocrine tumors

These tumors begin to show in the neuroendocrine cells (nerve cells responsible for regulating hormone production). These tumors have slow-growing cells that most commonly develop in the gastrointestinal tract and lungs. They can be found rarely in the genitourinary tract.

A subset of neuroendocrine tumors is carcinoid tumors which account for approximately 1% of all colon cancers and 50% of all cancers of the small intestine. They are very slow-growing.

Symptoms

Patients can have different symptoms depending on where the tumor develops. Generalized symptoms include:

• Loss of appetite

• Lethargy

• Unintentional weight loss

More specific symptoms depend on the site:

• Appendix: The tumor may start to block the appendix-intestine pathway causing appendicitis symptoms such as nausea, vomiting, and fever.

• Small intestine or colon: Bloating, abdominal pain, and cramps, changes to bowel habits.

• Rectum: Bleeding, feeling of “fullness” in the rectum or incomplete bowel movements, pain, changes in bowel habits.

Neuroendocrine tumors may also produce hormones that cause symptoms related to a particular hormone. This is termed “carcinoid” syndrome and was previously used as a name for these cancers even though not all of them cause the syndrome.

Tumors may release certain hormonal substances⁴ that cause diarrhea, rapid heartbeat, flushing in the face, and wheezing. This is most often associated with neuroendocrine tumors of the small intestine.

Diagnosis

Discovering carcinoid tumors depends on where they develop. For instance, appendicitis may signal the presence of tumors in the appendix, which calls for appendix removal. Routine checkups can help detect rectal tumors. The tests that help diagnose carcinoid tumors include imaging scans, blood tests, endoscopy, colonoscopy, and urine tests.

Treatment

• Surgery 

• Chemotherapy 

• Radiation therapy 

• Hormone therapy

Rare types of colorectal cancer

1. Primary colorectal lymphomas

This type of colorectal cancer grows in the lymphatic system in the lymphocyte cells. These are white blood cells that help your body fight infections. It may develop in different parts of the body, including the bone marrow, thymus, spleen, lymph nodes, and digestive tract. Primary colorectal lymphoma is more common in males and accounts for 0.5% of all colon cancers and around 5% of lymphomas.

Symptoms

• Bloating

• Indigestion

• Stomach pain 

• Diarrhea

• Vomiting 

• Unexplained weight loss

Diagnosis

• Biopsy

• Endoscopy

Treatment options

• Chemotherapy 

• Surgery 

• Radiation therapy

2. Gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are a rare type of colon cancer (1-2% of diagnoses) that develops in the special cells (interstitial cells) present in the gastrointestinal (G.I.) tract walls.

Over 50% of GISTs start in the stomach, while most others form in the small intestine and rectum. They fall under the classification: sarcomas or cancers that start in the connective tissue, including blood vessels, nerves, deep skin tissues, fat, cartilage, and bones.

Estimates are uncertain, but the ACS⁵ notes that the U.S. has between 4,000 and 6,000 GIST cases. The tumors may take a while to develop to the point of starting to cause symptoms. However, they may cause gastrointestinal tract bleeding.

Patients may find blood in their stool or vomit, depending on the location of the tumors. With time, slow bleeding may cause anemia or a decline in the number of red blood cells, and the patient begins to feel weak and fatigued.

Other possible symptoms

• Vomiting 

• Abdominal pain 

• Nausea 

• Swallowing problems 

• Weight loss 

• Poor appetite 

• Abdominal mass or lump

Diagnosis

• Endoscopy

• Colonoscopy

• Biopsy

• Various imaging tests

3. Leiomyosarcomas

Leiomyosarcoma (cancer of the muscle) is another form of sarcoma. It affects three muscle layers in the colon and rectum, all of which work together to direct waste through the digestive tract. Leiomyosarcomas account for about 0.1% of all colon cancers. 

In the initial stages, this cancer may not cause symptoms in the colon or rectum. As cancer progresses, a patient may experience symptoms such as:

• Vomiting blood

• Weight loss

• Fatigue

• Changes in stools

Diagnosis

• Biopsy

• Blood tests

• Imaging tests

Treatment

• Surgery for tumor removal

• Radiation therapy

• Chemotherapy

4. Melanomas

Melanomas are closely related to skin cancer. They may develop anywhere, including in the rectum or colon, or spread to the G.I. tract from the primary melanoma site. This type of colon cancer accounts for 1-3%⁶ of all cancers that start in the digestive system. However, its development is rare and not well understood.

Diagnosis

• Biopsy  

• Other tests determine whether cancer spread from elsewhere in the body or began in the colon or rectum.

Treatment

• Surgery 

• Radiation therapy 

• Immunotherapy 

• Chemotherapy

5. Squamous cell carcinomas

Squamous cell carcinomas (SCC) are less common in the colon than on the skin (it is the second most common type of skin cancer), with not more than 100 cases diagnosed, according to a 2017 case report⁷.

Symptoms

• Blood in stool 

• Thin stools 

• Unexplained weight loss 

• Painful and tender abdomen 

• Changes in bowel habits

SCC symptoms resemble those of colorectal adenocarcinoma.

Diagnosis

• Colonoscopy 

• Other tests

It's essential to establish whether cancer began in the colon or rectum or spread from other body regions.

Treatment

• Surgery 

• Chemotherapy 

• Radiation therapy

Syndromes associated with colon cancer

1. Familial adenomatous polyposis (FAP)

Familial adenomatous polyposis (FAP) accounts for about 1% of cancers in the rectum or colon⁸. Patients with this syndrome may develop hundreds or thousands of colon or rectal polyps.

It is most often due to an inherited mutation of a tumor suppressor gene, so, usually, a parent will be affected. However, 25% of patients have spontaneous FAP.  This gene normally stops abnormal cell activity, so when it is mutated, abnormal cells (cancer) can develop.

The polyps may occur at ten-12 years of age but are most commonly found between 20-40 years of age. Almost everyone with this syndrome develops colon cancer in their lifetime. If there’s a family history, then early screening is key. The doctor may recommend colon removal as a preventative measure.

2. Peutz-Jeghers syndrome (PJS)

PJS is a syndrome inherited from one parent that results from mutations in another tumor suppressor gene (STK11). The condition leads to the development of a certain type of polyp in the gastrointestinal tract.

It increases the risk of colon cancers and others such as pancreatic, ovarian, and breast cancer. If colon cancer does occur in patients with PJS syndrome, it develops at a younger age than the average.

3. Familial colorectal cancer

Genetic syndromes inherited from parents increase the risk of getting colon cancer. The syndromes come with genes that increase the risk of cancer development.

An example is Lynch syndrome, associated with about 2-4%⁹ of all cancers in the rectum or colon and often causes endometrial cancer. Having this syndrome increases the risk of getting colon cancer by up to 50%. These patients develop cancer at an earlier age than the average.

How colon cancer spreads

The colon and rectum walls consist of multiple layers. Colon cancer develops in the interior layer (mucosa) and can spread outward via some or all the other layers.

Cancers present in the wall can grow into lymph vessels or blood vessels and then travel to the adjacent lymph nodes or other parts of the body. The colon cancer stage depends on how deeply it spreads into the wall and grows outside the rectum or colon.

The lowdown

Screening for colon cancer is critical to ensure it's detected early so that treatment can begin as soon as possible. Even if you don't have symptoms and your family has no historical background of colorectal cancer, you have an average chance of getting it. You should see your doctor for regular screening between 45 and 75 years of age.