Cancer Types   /   Gastrointestinal Cancers

Understanding Your Pathology Report: Colon Cancer

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Carolyn Vachani, MSN, RN, AOCN
Abramson Cancer Center of the University of Pennsylvania
Last Modified: June 10, 2007

What is a pathology report?

A pathologist is a doctor who specializes in diagnosing diseases by examining tissue from the body. You will probably never meet the pathologist, but samples of your colon tissue, removed during surgery or biopsy, will be sent to him or her for review. The pathologist prepares a report of their findings, which is called the pathology report.

What will you find on a pathology report?

The report is broken down into a few sections, including some information about the patient, diagnosis (if known), procedure, a description of what the specimen looks like to the naked eye (called gross description), a description of what was seen under the microscope (microscopic description), and a diagnosis. In the case of a colon cancer, the pathologist will describe the type of cell the cancer comes from, how deeply the tumor goes into the colon wall, the histologic grade of the tumor, if there is vascular invasion and if any lymph nodes are involved. To help you read your report, let's go through each of these sections individually.

The Gross Description

This is generally not that important to you, the patient. It is a description of what the pathologist received and what they see with the naked eye. In a biopsy, the specimen is likely a small, nondescript piece of tissue, in which case the pathologist may describe the color, shape, feeling and size of the tissue. After a cancer surgery, multiple organs or tissues may be submitted and described in the report. This might include size, color and weight. For example, a colon specimen from a colectomy may be described as:

Specimen #1 is labeled “colon” and consists of a segment of bowel measuring 13cm in length after fixation. The specimen is surrounded by a moderate amount of pericolonic fat. 3cm from one resection margin is an ulcerated round tumor measuring 3.2cm in diameter. The rest of the mucosa is grossly unremarkable.

This tells us the specimen was a 13cm long piece of colon, with a tumor located 3cm from one end. This isn't very helpful in determining stage or treatment, so let's move on to the next section.

Microscopic Diagnosis

This section may be called microscopic diagnosis or just diagnosis. This is the meat of the report, but we need to understand a bit about the colon in order to understand this part of the report. The colon, or large intestine, is a tube that is about 5 to 6 feet in length; the first 5 feet make up the colon, which then connects to about 6 inches of rectum, and finally ends with the anus. The colon is made up of several sections and your report may specify which section the tumor was located in. These sections are called the cecum, ascending, transverse, descending and sigmoid colons, rectum and anus (see diagram). The splenic and hepatic flexures are areas where the colon bends (or flexes) that are named for the organs they are located near.

The colon, which is shaped like a tube, is made up of several layers, starting with the innermost layer, the mucosa (which is made up of epithelium), and then the lamina propria and muscularis mucosa. This is surrounded by the submucosa, which is surrounded by two layers of muscle (or muscularis), and finally, the serosa layer, which is the outside layer of the tube. The outside of the colon is covered with a layer of fat, also called adipose tissue, which contains lymph nodes and blood vessels which feed the colon tissue.

Now that we understand a bit about the anatomy of the colon, let's go through the things you might see in this section of the report.

Tumor Cell Type

The type of colon tumor describes the cells from which the tumor arises. Adenocarcinoma is the most common type, accounting for 95-98% of colon cancers. An adenocarcinoma arises from the glandular cells that line the inside of the colon. Two subtypes of adenocarcinoma are signet ring and mucinous, which are both named for the way the cells look under the microscope. The other 2-5% of cancers found in the colon are lymphomas, GIST, and carcinoid tumors, which will not be discussed in this article.

If a polyp was removed, this section will describe the type of polyp. A colon polyp is a benign growth that, over time, can turn into cancer. For that reason, they are removed during a colonoscopy and may be sent to the pathologist to determine what type of polyp it is. There are several types of polyps that can be found in the colon:

• Tubular adenoma (also called adenomatous polyp): this accounts for 70% of the polyps found in the colon and can progress into cancer, but this happens over many years. If they are found early, they can be removed during colonoscopy.
• Villous adenoma: this accounts for 15% of the polyps found in the colon. This type of polyp has the highest risk of turning into cancer. In some cases these can be removed during colonoscopy, but in other cases surgery is required.
• Hyperplastic polyps and Inflammatory (or pseudopolyps): these two types of polyps are not likely to turn into a cancer.

In addition, colon polyps come in two forms, called pedunculated and sessile. Pedunculated polyps grow on a stalk and look like a small mushroom, which can usually be easily removed during a colonoscopy. The sessile type of polyp is flat and grows on the wall of the colon. These are much more difficult to remove and may require surgery to remove the entire polyp.

Histologic Grade

As normal cells develop, they “differentiate” to become a specific type of cell. Histologic grade describes how closely the tumor cells resemble normal cells. The more a tumor cell looks like a normal cell, the more well differentiated it is. This is broken down into three grades:

• Grade 1: also called well differentiated. Cells appear the most normal.
• Grade 2: also called moderately differentiated.
• Grade 3: also called poorly differentiated. Cells appear the most abnormal and tend to grow more aggressively.

Depth of Invasion

A tumor that has not invaded the surrounding tissues is sometimes called “in situ”, while tumors that have penetrated surrounding tissues are called invasive. The diagnosis section will include information on the layers of the colon that the tumor has invaded (see the diagram of the colon layers) and if it has extended beyond the colon into surrounding tissue. Some examples include:

• “The biopsy shows involvement of the mucosal lamina propria by neoplastic glands. The submucosa is not involved.” This tumor invades only the innermost layer of the colon.
• “The tumor invades through the muscularis propria but not into the pericolonic adipose tissue. The serosal surface is not involved.” This tumor invades the muscle layer, but does not invade the serosa (the outer layer of the colon) or the surrounding fat.
• “The tumor is invasive through the muscularis propria into the pericolonic fat.” This tumor has penetrated through the colon wall and into the surrounding fat.

Lymphovascular Invasion

When the pathologist examines the tumor and surrounding tissue available to them, they look at the tiny blood vessels and lymphatic drainage to see if any tumor cells have invaded them. This is different from the lymph nodes and would be reported as whether or not lymphovascular invasion is seen. The presence of this may be a sign of a more aggressive tumor.

Lymph Nodes

The lymph system is essentially the "housekeeping system" of the body. It is a network of vessels (tubes) which connect lymph nodes. These nodes can vary in size, but are normally up to about 2 centimeters in width. They contain cells that clear bacteria and other foreign debris from the body. Lymph is a watery liquid that flows between cells in the body, picking up foreign debris and taking it into the lymph node for filtering and ultimately, elimination by the liver.

Cancer cells use the lymph system as a first step to traveling to other areas of the body. During a colon cancer surgery, numerous lymph nodes are removed and checked for the presence of cancer cells. This will be reported as the number of lymph nodes that contained cancer cells and how many were examined. For example, the report might state “fifteen benign lymph nodes (0/15)” or “tumor seen in sixteen of twenty lymph nodes (16/20).”

In a colon cancer surgery, the more lymph nodes removed the more certain you can be that no lymph nodes are involved. It is not uncommon to have as many as 30 lymph nodes removed during a colon cancer surgery. This is different from many other types of cancer, where far fewer nodes are removed.

Margins

Your report may comment on margins. This is the area at the edge of the specimen that was submitted. When performing a cancer surgery, the surgeon attempts to remove the entire tumor and some normal tissue surrounding it. This area of “normal tissue” is important because any stray cancer cells may be included in this. If the edge (or margin) contains tumor, there may have been cancer cells left behind. The goal of surgery is to achieve a “clear margin”, that is, clear of any cancer cells.

Size

Your report may or may not specify the actual size of the tumor. While size can be important, in colon cancer, depth of invasion is most important.

Putting it all together

All of these pieces are used to determine the stage of the cancer and what treatment is needed. By understanding the basics of the report, you will be better able to discuss your treatment options with your healthcare team. The staging system most commonly used for colon cancers is the American Joint Committee on Cancer (AJCC) staging system. This system utilizes the extent of the primary tumor (Tis-4), the absence or presence of cancer in the lymph nodes (N0-2), and the existence of metastasis (M0 or 1) to assign a TNM rating, which corresponds to a stage. The TNM rating is broken down as follows:

T Stages

• Tis: This stage is also called carcinoma in situ. The cancer involves the mucosa and has not grown beyond the muscularis mucosa.
• T1: The cancer has invaded the submucosa.
• T2: The cancer has invaded the muscularis propria.
• T3: The cancer has grown completely through the muscularis propria into the serosa layer, but not into any neighboring tissues.
• T4: The cancer has grown through the colon wall and invades other organs or tissues.
• Tx is used if the tumor cannot be assessed and T0 is used if no evidence of tumor is seen.

N Stages

• N1: Cancer is seen in 1 to 3 lymph nodes.
• N2: Cancer is seen in 4 or more lymph nodes.
• N0 is used if no tumor is seen and Nx is used if the lymph nodes cannot be assessed.

M Stages

• M0: The cancer does not appear to have spread to other organs such as lung, liver and bone.
• M1: The cancer has spread to other organs such as lung, liver and bone.
• Mx: Spread of the cancer has not been evaluated.

Now these ratings are combined to come up with a stage for the cancer. The Duke's staging system is an older system that is not as precise at describing the tumor, but you may still hear it used.

• Stage 0 (also called carcinoma in situ) (TisN0M0): the cancer is confined to the outermost portion of the colon wall.
• Stage I (T1 or 2, N0, M0): the cancer has spread to the second and third layer of the colon wall, but not to the outer colon wall or beyond. This is also called Dukes' A colon cancer.
• Stage IIA (T3, N0, M0): Cancer has spread beyond the middle tissue layers of the colon wall or has spread to nearby tissues around the colon.
• Stage IIB (T4, N0, M0): Cancer has spread beyond the colon wall into nearby organs and/or through the peritoneum. Dukes' B colon cancer describes both stage II A&B.
• Stage IIIA (T1 or 2, N1, M0) the cancer has spread through the submucosa or muscle layer and into 1-3 lymph nodes, but has not spread to other areas of the body.
• Stage IIIB (T3 or 4, N1, M0): The tumor has grown through the colon wall and may involve nearby tissues and has invaded 1-3 lymph nodes, but has not spread to other areas of the body.
• Stage IIIC (Any T, N2, M0): This stage can be any T rating, but has invaded 4 or more lymph nodes and has not spread to other areas of the body. Dukes' C colon cancer is used to describe all stage III tumors.
• Stage IV (Any T, Any N, M1): the cancer has spread to other areas of the body (i.e. liver, lungs). This is also called Dukes' D colon cancer.

Read OncoLink's Overview of Colon Cancer.