by Ipshita Kak MD FRCPC, reviewed on April 25, 2019
The colon is a part of the gastrointestinal tract which also includes the mouth, esophagus, stomach, small bowel, and anus. The colon is a long hollow tube that starts at the small bowel and ends at the anal canal. The colon is divided into sections which include the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.
The functions of the colon are to absorb water from the food that we eat and to move waste out of the body.
The colon is made up of six layers of tissue:
Adenocarcinoma of the colon is a type of cancer that develops from the glands in the mucosa on the inner surface of the colon. It can develop anywhere along the length of the colon (from the cecum to the rectum). Adenocarcinoma is the most common type of cancer to arise in the colon and is typically just called ‘colon cancer’.
In many cases, this cancer starts in a pre-cancerous condition called an adenoma. An adenoma is called pre-cancerous because it has the potential to turn into a cancer overtime.
In contrast to cancer, the abnormal cells in an adenoma are only found within the mucosa on the inside of the colon. Once the cells spread beyond the mucosa into the submucosa the diagnosis becomes adenocarcinoma. The movement of abnormal cells into the tissue outside the mucosa is called invasion.
A biopsy is a surgical procedure that removes a small piece of tissue for examination by a pathologist. The purpose of a biopsy is to establish a diagnosis. A test called immunohistochemistry may be performed to confirm the diagnosis.
Other information that may be included in your biopsy report are tumour grade and extension into the wall of the colon. Your doctors will use this information to plan treatment such as surgery, radiation, and chemotherapy. Continue reading to learn more about tumour grade and extension in adenocarcinoma.
After the tumour has been removed completely, it will be sent to a pathologist who will prepare another pathology report. This report will confirm or revise the original diagnosis and provide additional important information such tumour size, extension, and spread of tumour cells to lymph nodes. A test to look for mismatch repair proteins may also be performed. This information is used to determine the cancer stage and to decide if additional treatment is required. Continue reading to learn more about the information found in this report.
Grade is a word pathologists use to describe how different the cancer looks compared to the normal tissue in the colon. Because the normal epithelial cells in the colon connect together to make glands, adenocarcinoma is usually divided into four grades based on how much of the tumour is made of glands:
After the tumour has been removed fully, your pathologist will measure it in three dimensions although only the largest dimension is typically included in your report. For example, if the tumour measures 5.0 cm by 3.2 cm by 1.1 cm, the report may describe the tumour size as 5.0 cm in greatest dimension.
All adenocarcinomas start in the mucosa on the inside surface of the colon. The layers of tissue below the mucosa include the submucosa, muscularis propria, subserosal adipose tissue, and serosa. The movement of cancer cells from the mucosa into the tissue below is called invasion.
Tumour extension is a way of describing how far the cancer cells have traveled from the mucosa into the tissue below. Your pathologist will carefully examine your tissue to find the cancer cells that have traveled the furthest from the mucosa.
Cancer cells that travel deeper in the wall are more likely to come back in the area of the original tumour (local recurrence) after treatment or to spread (metastasize) to a lymph node or distant site such as the lungs. Tumour extension is also is used to determine the tumour stage (see Pathologic stage below).
Nerves are like long wires made up of groups of cells called neurons. Nerves send information (such as temperature, pressure, and pain) between your brain and your body. Perineural invasion is a term pathologists use to describe cancer cells attached to a nerve.
Perineural invasion is important because cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour.
Perineural invasion is also associated with a higher risk that the tumour will come back in the same area of the body (local recurrence) after treatment.
Lymphatics and blood vessels are channels that normal cells use to travel around the body. The presence of cancer cells within a lymphatic or blood vessel is called lymphovascular invasion and is associated with a higher risk that tumour cells will travel to either a lymph node or a distant site such as the lungs.
The presence of cancer cells inside a large vein past beyond the wall of the colon (outside of the thick bundle of muscle) is associated with a high risk that the cancer cells will eventually be found in the liver.
In the colon, a margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. The colon is a long tube and your surgeon will need to cut out a portion of the tube in order to remove the tumour from your body. The two cut ends of the tube are called the proximal and distal margins. The radial margin is any tissue around the tube that needs to be cut.
In the colon, a margin is considered positive when there are cancer cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment.
A tumour deposit is a group of cancer cells that are separate from the main tumour but not in a lymph node. The presence of tumour deposits is associated with a higher risk that the cancer will travel (metastasize) to a distant body site such as the lungs after treatment.
Tumour budding refers to either single cancer cells or small groups of cancer cells seen at the edge of the tumour. A score is assigned, either low, intermediate, or high, based on the number of buds seen under the microscope. A high score is associated with increased risk that cancer cells will be found in a distant location (metastasize).
Occasionally the cancer cells are still contained to the polyp that gave rise to the tumour. If the cancer cells are limited to the inner surface of the polyp and the polyp is removed completely, there is very little chance that the cancer will come back.
The risk that the cancer will come back in the future is increased if your pathologist sees any of the following features under the microscope:
If you received treatment (either chemotherapy or radiation therapy or both) for your cancer prior to the tumour being removed, your pathologist will carefully examine the area of the tissue where the tumour was previously identified to see if any cancer cells are still alive (viable).
The most commonly used system describes the treatment effect on a scale of 0 to 3 with 0 being no viable cancer cells (all the cancer cells are dead) and 3 being extensive residual cancer with no apparent regression of the tumour (all or most of the cancer cells are alive).
Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called a metastasis.
Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells.
Your pathologist will carefully examine all lymph nodes for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative.
Why is this important? Finding cancer cells in a lymph node is important because it is associated with a higher risk that the cancer cells will be found in other lymph nodes or in a distant organ such as the lungs.
The pathologic stage for colonic adenocarcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer.
This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and worse prognosis.
Adenocarcinoma is given a tumour stage between 1 and 4 based on the distance the cancer cells have traveled from the mucosa into the wall of the colon or surrounding tissues (tumour extension).
Adenocarcinoma is given an nodal stage between 0 and 2 based on whether any cancer cells were found in any of the lymph nodes examined or the finding of tumour deposits.
If no cancer cells were found in any of the lymph nodes examined, the nodal stage is N0.
If no lymph nodes were sent for pathologic examination, the nodal stage cannot be determined and is listed as NX.
Adenocarcinoma is given a metastatic stage between 0 and 1 based on the presence of cancer cells at a distant site in the body (for example the liver). The M stage can only be assigned if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely present, the M stage cannot be determined and is listed as X.
Mismatch repair (MMR) is a system inside all normal, healthy cells for fixing mistakes in our genetic material (DNA). The system is made up of different proteins and the four most common are called MSH2, MSH6, MLH1, and PMS2. A loss of one of these proteins increases the risk of developing cancer. Pathologists order mismatch repair testing to see if any of these proteins are lost in a tumour. If maismatch repair tested has been ordered on your tissue sample, the results will be described in your pathology report.
Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce piece of the machine called a protein.
If the DNA becomes damaged or if it cannot be read accurately, the cell will be unable to produce the proteins it requires to function normally. An area of damaged DNA is called a mutation and mutations are one of the most common causes of cancer in humans. Mismatch repair proteins keep cells healthy and functioning normally by fixing these mutations when they happen.
The four mismatch repair proteins MSH2, MSH6, MLH1, and PMS2 work in pairs to fix damaged DNA. Specifically, MSH2 works with MSH6 and MLH1 works with PMS2. If one protein is lost, the pair cannot function normally.
For most people, cancer develops as a result of both environmental factors (for example smoking) and genetic factors. These tumours are called ‘sporadic’ because we cannot predict exactly which people will develop them and when.
Some people, however, inherit genetic changes that put them at a much higher risk for developing cancer. These people are said to have a syndrome.
Lynch syndrome is caused by a genetic change that results in the loss of one of the mismatch repair proteins. Another name for this syndrome is hereditary nonpolyposis colorectal cancer (HNPCC).
The most common genetic changes associated with Lynch syndrome involve the genes that produce MLH1 and MSH2. A small number of people with Lynch syndrome will show genetic changes involving MSH6 and PMS2.
People with Lynch syndrome are at high risk for developing adenocarcinoma of the colon at an early age. Women with Lynch syndrome are also at risk for developing ovarian and endometrial cancer at an early age. Other types of cancers associated with Lynch syndrome include stomach, liver, bladder, skin, and brain.
Muir-Torre is a syndrome that is closely related to Lynch syndrome. People with Muir-Torre are at high risk for developing a type of skin cancer called sebaceous carcinoma. These people are also at risk for developing multiple non-cancerous skin tumours called sebaceous adenomas.
The most common way to test for mismatch repair proteins is to perform a test called immunohistochemistry. This tests allows pathologists to see if the tumour cells are producing all four mismatch repair proteins.
If the tumour cells are not producing one of the proteins, your report will describe this protein as “lost” or “deficient”. Because the mismatch repair proteins work in pairs (MSH2 + MSH6 and MLH1 + PMS2), two proteins are often lost at the same time.
If the tumour cells in your tissue sample show a loss of one or more mismatch repair proteins, you may have inherited Lynch syndrome and should be referred to a genetic specialist for additional tests and advice.