Types of Colon Cancer

An Overview of Each Type of Colon Cancer

medical chart with the words diagnosis and colon cancer
What are the different types of colon cancer?. Istockphoto.com/Stock Photo©designer491

Are there different types of colon cancer like there are different types of other cancers? How are these alike, and how are they different? Where do most cancers occur?

An Overview of The Types of Colon Cancer

Colon cancer is diagnosed too often and takes too many lives, being the 3rd leading cause of cancer-related deaths in men and the 3rd most common cause of cancer-related deaths in women.

There are several different types of colon cancer.

Some of these, such as adenocarcinoma, are very common, whereas some types are fairly uncommon. While there are some similarities between the forms of colon cancer there are many important differences, including the best treatments, the prognosis, and the chance that they run in families.

You may also be wondering if there is a difference between colon cancer and colorectal cancer. These terms are often used interchangeably, but there are some differences between cancers which occur in the rectum and those that occur higher up in the colon, particularly when it comes to surgical approaches.

Colon Cancer Tissue Types

In describing the different types of cancer it can be helpful to understand about the different tissue types that can become cancerous. Cancers are broken down in many ways, for example, by organ system such that colon cancer is considered a digestive tract cancer. How a cancer behaves, no matter what organ it starts in, however, often has more to do with the type of tissue in which it starts.

The different tissue types that may give rise to cancers include:

  • Carcinomas - Carcinomas are cancers of epithelial tissue, the tissues which line body cavities and cover organs. Around 85 percent of cancers are carcinomas.
  • Sarcomas - Sarcomas arise from cells known as mesothelial cells and are cancers of connective tissue and soft tissues such as bone, ligaments, muscle, fat, and cartilage.
  • Myelomas - Myelomas arise in cells of the immune system called plasma cells.
  • Leukemias - Leukemias are cancers of one of the type of white blood cells.
  • Lymphomas - Lymphomas begin in they type of white blood cells in the immune system known as lymphocytes.
  • Mixed types including neuroendocrine tumors - Specialized cell types such as those that regulate digestion are included in this category.

Types of Colon Cancer

Based on the tissue types above, colon cancers may be broken down into:

Adenocarcinomas

Adenocarcinomas are the most common type of colon cancer, accounting for 90 to 95 percent of colorectal cancers. These cancers originate in the glands (mucus secreting glands) of the colon. In addition to "regular" adenocarcinomas, there are two main subtypes:

  • Mucinous (colloid) adenocarcinomas - These cancers account for 10 to 15 percent of adenocarcinomas, and due to their production of mucus which allows easier spreading of cells, are thought to metastasize more quickly than some other colon cancers.
  • Signet ring cell adenocarcinomas of the colon - The signet ring subtype is uncommon, comprising less than 0.1 percent of adenocarcinomas. These cancers are named for their appearance. They have a large amount of fat, which when dehydrated pushes the nucleus to one side of the cell giving it the appearance of a signet ring.

Adenoarcinomas begin as adenomas, benign polyps of the colon. Since these cancers have a precancerous form, screening tests such as colonoscopy may prevent (through the removal of the precancerous polyp) cancer from developing or find it in the early stages.

The formation of adenocarcinomas from adenomas is fairly linear, meaning the larger the polyp, the greater the chance that it will become malignant. When a polyp has reached 2 cm (about an inch) in size, it has a 30 percent to 50 percent chance of being cancerous.

Leiomyosarcomas

Leiomyosarcomas begin in the smooth muscle cells of the colon and comprise less than two percent of colon cancers. Symptoms, including bleeding and pain tend to occur when these cancers have already spread.

Since the cells making up leiomyosarcomas do not have what is known as a basement membrane, there is not a precancerous stage. In other words, screening tests are unable to find these cancers before they become a cancer.

Lymphomas

Colorectal lymphomas are uncommon and are more likely to start in the rectum than in the colon. However, lymphomas that start somewhere else in the body are more likely to spread to the colon than to the rectum. Lymphomas are cancers of the immune system which begin in the type of white blood cells known as lymphocytes.

Non-Hodgkins lymphoma accounts for about 0.5 percent of all colorectal cancers and has many forms including MALT lymphoma, follicular cell lymphoma, large B cell lymphoma, anaplastic large cell lymphoma, and others.

Colon and rectal lymphomas are often diagnosed in the later stages, with half of people having stage 4 disease (metastatic lymphoma) at the time of diagnosis.

Melanomas

Melanomas of the colon and rectum are uncommon, and most melanomas that are found in the rectum are due to the spread (melanoma metastases) from melanomas elsewhere in the body. Overall they account for less than two percent of cancers in the colon and rectum.

Neuroendocrine Tumors

Neuroendocrine tumors account for around four percent of colorectal cancers a These tumors arise in nervous system type tissues.and are broken down into two categories:

  • Aggressive Neuroendocrine Tumors of the Colon and Rectum - Aggressive neuroendocrine tumors account for around four percent of colon cancers. These tumors are again broken down into two categories: large cell and small cell neuroendocrine tumors. They tend to be diagnosed in the later stages and in general have a poor prognosis.
  • Indolent Neuroendrocine Tumors of the Colon (Carcinoid Tumors) - These cancers tend to grow slower and are less invasive than aggressive neuroendocrine cancers. In some ways they tumors act a lot like benign tumors, but unlike benign tumors, they do have the ability to spread (metastasize). That said, the chance that they will spread is very low. They account for less than one percent of colon cancers overall, and are more likely to be found in the small intestine than in the colon. These cells make hormones that sometimes, if large amounts of hormones are made or if the tumor spreads to the liver, can cause a constellation of symptoms referred to as carcinoid syndrome. Symptoms often include hot flashes associated with the abrupt onset of flushing, bloating, and other symptoms.

It's been found that people with aggressive neuroendocrine tumors are often first misdiagnosed as having carcinoid tumors, so it's important to talk with your doctor and consider a second opinion if you are diagnosed with an indolent neuroendocrine tumor.

Stromal Tumors

Stromal tumors are cancers that develop in cells in the digestive tract that act to regulate the digestion of food. They are uncommon tumors and are more likely to occur in the stomach than in the colon. They begin in cells known as the interstitial cells of Cajal or ICC's. Some of these tumors are cancerous whereas others are benign tumors.

Where are Most Colon Cancers Located?

After learning about the types of colon cancer, and that some types are more common in certain locations, you may be wondering where in the colon most colon cancers are located. They are broken down as follows:

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

Bottom Line on Types of Colon Cancer

Recognizing that there are many differences between the different types of colon cancer and also where they are located helps to explain why everyone is different when it comes to the best treatment recommendations and prognosis of their cancer. It's common for people who have been diagnosed with cancer to understand these differences when they receive the inevitable recommendations from family and friends on what they should do and who they should see based on another person's tumor. If these comments are beginning to bother you, you may wish to gently point out that there are as many different varieties of colon cancer as there are of people, and each colon cancer needs to be looked at independently based on it's tissue type, it's location, and many other characteristics as well.

Sources:

National Cancer Institute. Colon Cancer Treatment (PDQ) – Health Professional Version. Updated 08/12/16. https://www.cancer.gov/types/colorectal/hp/colon-treatment-pdq

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