Types of Colon Cancer

Treatment directed by size, stage, and location of tumor

Colorectal Cancer Image

Colon cancer is the third most common cancer in the U.S., accounting for around 110,000 cases each year. Sadly, it is also the second leading cause of cancer-related deaths among both men and women.

The term colon cancer is sometimes used interchangeably with colorectal cancer, the latter of which involves both the colon and adjacent rectum. Of cancers specifically affecting the rectum, around 40,000 cases are diagnosed each year.

Colon cancer is not just one type of cancer. It involves many different types of malignancy which vary in their location, cell structure, symptoms, and speed of progression. These differences can direct the way in which treatment is delivered and help doctors predict the likely outcome of the disease.

Colon Cancer Tissue Types

Colon cancers are largely differentiated by the type of tissue involved. That, in conjunction with the location of the tumor, can change the way in which an organ functions, resulting in specific and often characteristic symptoms.

Some cancers are less common than others and may be difficult to diagnose, either because of their location or their lack of clearly defined structure. It is for these reasons that certain cancers are more commonly seen when they are advanced and more difficult to treat.

As a whole, cancers can be broadly categorized as follows:

  • Carcinomas are cancers of epithelial cells that line canals and hollow structures.
  • Sarcomas affect mesothelial tissues covering organs.
  • Myelomas affect cells of the immune system called plasma cells.
  • Leukemias are cancers of white blood cells called leukocytes.
  • Lymphomas affect white blood cells called lymphocytes.
  • Mixed types that involve different types of cells.

Types of Colon Cancer

Based on the tissues involved, colon cancers be further broken down into various types and subtypes, each with their own unique behaviors and characteristics:

  • Adenocarcinomas are the most common type of colon cancer, accounting for 90 to 95 percent of diagnoses. These cancers originate in the mucus-secreting glands of the colon. In addition to typical adenocarcinomas, there are two subtypes: mucinous adenocarcinomaswhich produce excessive mucus and tend to spread (metastasize) quickly, and signet ring adenocarcinomas which are extremely rare and are considered more aggressive.
  • Leiomyosarcomas begin in the smooth muscle cells of the colon and comprise less than two percent of colon malignancies. Symptoms, including pain and bleeding, tend to occur when the cancer has already metastasized. Leiomyosarcomas can be very unpredictable and have a high rate of recurrence. It does not respond well to chemotherapy or radiation and is best removed surgically when small.
  • Colorectal lymphomas are uncommon and are more likely to start in the rectum than in the colon. Non-Hodgkins lymphoma accounts for around 0.5 percent of all colorectal cancers and is most often diagnosed in advanced disease.
  • Colorectal melanomas are also uncommon and tend to be found in the rectum as a secondary cancer (caused by the spread of cancer from other parts of the body). Overall, they account for less than two percent of cancers in the colon and rectum
  • Neuroendocrine tumors account for around four percent of colorectal cancers These tumors arise in nervous system tissues.and are broken down into two categories: aggressive neuroendocrine tumors which tend to spread quickly and have a poor prognosis and indolent neuroendocrine tumors which are slower and less invasive.
  • Gastrointestinal stromal tumors (GISTs) start from specialized cells in the colon called the interstitial cells of Cajal. They can be found anywhere in the digestive tract but are less common in the colon. Some of these tumors are cancerous whereas others are benign.

Where Are Most Colon Cancers Located?

While cancer can develop in any part of the colon, there are certain places where tumors are most likely to be seen.

This is much of the investigation will be focused during a routine colonoscopy. Moving from the ileocaecal valve (which separates the small intestine from the colon) toward the rectum, the risk of cancer by location is as follows:

  • Ileocaecal valve: 2 percent
  • Ascending colon and caecum: 20 percent
  • Transverse colon: 10 percent
  • Descending colon: 5 percent
  • Rectum and sigmoid colon: 55 percent

Based on the type, stage, and location of the cancer, doctors can determine the best course of treatment to either cure the disease or better manage the symptoms if the cancer is not treatable.

Source:

National Cancer Institute. "Colon Cancer Treatment (PDQ) – Health Professional Version." Bethesda, Maryland; updated August 19, 2017.

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