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Introduction

 

Colorectal Cancer



What is Colorectal Cancer?

Colorectal cancer is a disease that results from the growth and reproduction of abnormal cells beginning to form in the lining of the colon or rectum. It is the cancer cell's ability to multiply continuously, invade normal tissue, and spread to other parts of the body (metastasize) that identifies it as malignant and potentially life threatening.


How Does a Colon or Rectal Cancer Develop?
Polyps are the most common precursors of colorectal cancer. Polyps are abnormal growths arising from the lining of the colon or rectum and protruding into the intestinal canal or lumen. The same genetic and lifestyle factors that cause colorectal cancer are believed to contribute to polyp formation.

As polyps grow they assume a greater risk of becoming malignant. The chance of a very small polyp being cancerous is less than one in five hundred. The chance of polyps of one or more centimeters being cancerous is about one in ten. The chance that a large polyp over two centimeters is cancerous may be as high as one in two.

Most polyps develop slowly and are benign for long periods of time. During this benign interval, they can be identified and removed, interrupting the very process that can lead to cancer. A polyp removed is a potential cancer prevented. Therefore, when a polyp is identified as a risk factor for colorectal cancer, patients can be reassured that regularly scheduled colonoscopic examinations can remove future polyps and prevent development of cancer. At the very least, colon and rectal cancer can be detected at their earliest stages, when a cure is most likely.


The Anatomy of the Colon and Rectum

A brief review of the anatomy of the colon and rectum will help you understand how your doctors are evaluating and treating your colorectal cancer.

The colon and the rectum are the last five feet of the digestive system. Together, they are also referred to as the large intestine, or large bowel. The colon is the upper five feet of the large intestine, and the rectum is the lower six inches.

The function of the colon is largely involved with preparation of solid waste stool. After food is digested in the stomach and small intestine, it moves into the colon, where any remaining water is absorbed into the body, leaving solid waste, or stool. Stool moves through the colon and rectum, leaving the body through the anus.

While the colon is mainly situated in the abdomen, the rectum is primarily a pelvic organ. Although they are often grouped together as colorectal cancer, it is the rectum's proximity to other pelvic organs that creates their differences.

Think of the colon and rectum as an inverted pyramid, with the lower half being much narrower than the upper. The upper part, or the colon, resides in the much roomier structure of the abdomen. The lower part, or rectum, is crowded within the narrow pelvis. It is further surrounded by other pelvic organs such as the ovaries and other genital organs in women, the prostate in men and the bladder in both men and women. In the rectum, the challenge for the surgeon is to completely remove the rectal cancer and any affected surrounding tissue without damaging these other organs or their normal functions.



Similar to all other organs in the body, the colon and rectum have a blood supply of arteries and veins. Along these blood vessels are lymph nodes. Lymph nodes are structures, normally about the size of peas, that produce and store cells that fight infection, inflammation, foreign proteins and cancer.



The Microscopic Anatomy of the Bowel Wall

The colon and rectum is a hollow tube. The hollow part is the "lumen" and the tissue part is the "bowel wall". The bowel wall is actually composed of four distinct layers. Cancer begins in the mucosa, the lining of the colon facing the lumen. Cancer which is limited to this surface lining rarely has spread into surrounding lymph nodes or more distant organs, such as the liver or lungs, and it is very curable by surgery alone. However, tumors that are penetrating into the "deeper" layers of the bowel wall are already displaying an ability to invade into normal tissue. Generally, the deeper a tumor has penetrated the bowel wall, the more difficult it is to cure with surgery alone.

The extent to which a tumor has invaded the bowel wall is an important part of the TNM staging system, which is defined below.



The Stages of Cancer of the Colon and Rectum

Staging is a system by which widely accepted criteria are applied to categorize the extent to which cancers have advanced. These criteria are important because they allow physicians to speak about cancer using the same language. Staging is critical for predicting disease free and overall survival outcomes and in planning therapies.

In colon and rectal cancers, stage is determined by the extent to which a cancer has penetrated the thickness of the bowel wall, the presence or absence of lymph node metastases (areas of spread), or by spread to distant organs such as the liver, lung, bone or other sites. As the stage of primary cancer advances, the risk of metastasis increases.

Your physician may advise certain tests to help determine the presence or absence of spread, such as a CAT scans of the abdomen, pelvis or chest. A blood test call the carcinoembryonic antigen (CEA) may be useful for assessing response to therapy. However, not all tumors produce CEA.

Endoscopic ultrasound (EUS) involves inserting an instrument called a transducer via a flexible scope into the rectum. The transducer produces sound waves that result in an image of the primary tumor with surrounding lymph nodes and tissue. With this image, lymph node status and the depth of invasion of the rectal cancer can be accurately identified. With staging this precise, treatments such as chemotherapy and radiation oncology can be planned. This tool may be the best preoperative staging technique for rectal cancers.

Staging involves information obtained from the pathologist after he or she has examined the surgically removed tumor under a microscope. Staging involves a review of all clinical and pathologic findings and final staging is not available until the receipt of a final pathology report. Such a report is available several days after surgery.

Staging may be done according to different systems. One of these, such as the Dukes Classification (named after Sir Cuthbert Dukes, a British pathologist), has been in existence for over 75 years.

More recently, in an effort to standardize reporting and to add flexibility to staging, the TNM system sponsored by the International Union Against Cancer has been widely adopted:

T refers to the extent of the primary tumor which is related only to its depth of penetration into the bowel, not its size.

N refers to the presence or absence and the extent of regional lymph node metastasis.

M refers to the presence or absence of distant metastases to other sites of the body.

Stage 0
TIS ("IS" refers to in situ) N0 M0
This is early stage colon cancer that is confined to its site, in situ, or the first layer or surface lining without entering the submucosa. The designation of Stage 0 means that the cancer is not invasive and is not yet capable of spreading elsewhere.

Stage 1
T1 or T2 N0 M0
Also known as Dukes Stage A, the cancer has penetrated into, but not through, the bowel wall. The surrounding fat, or serosal surfaces, are not involved. There are no positive lymph nodes and there is no evidence of metastasis, or cancer spread. This is called localized cancer.

Stage 2
T3 NO M0
Also known as Dukes Stage B, the cancer has spread through the bowel wall into the surrounding fat, but does not penetrate the serosal surface or involve the regional lymph nodes.

Stage 3 any T N1-3 M0
Also known as Dukes Stage C, the cancer has penetrated the bowel wall and the regional lymph nodes are involved. A T4 tumor infiltrates a nearby organ, such as the urinary bladder, but the tumor is removable for cure.

Stage 4
any T any N M1
The cancer has spread beyond the colon, rectum or regional lymph nodes to distant sites or organs such as the liver or the lungs. In carefully selected situations, patients with metastatic colorectal cancer may be candidates for curative surgery of their metastatic disease. Other patients may be eligible for chemotherapy in order to minimize or prevent disease-related symptoms.



Who is at Risk for Developing Cancer of the Colon or Rectum?

Anyone in the general population can develop colorectal cancer. Of the 138,000 new cases per year, 100,000 are cancers of the colon and 38,000 are cancers of the rectum.

Colorectal cancer is almost evenly divided between men and women. Most individuals at risk for colorectal cancer are over the age of 40, and incidence rates peak between 60 and 65. Certain medical conditions, genetic factors, and personal habits, such as sedentary lifestyle and low-fiber/high-fat diet, increase an individual's risk of developing colorectal cancer.

There are some benign conditions that predispose individuals to colorectal cancer. However, these are rare and account for fewer than five percent of all colorectal cancer cases. These disorders include inflammatory bowel diseases such as ulcerative colitis and Crohn's disease. Because of the increased risk of colon cancer, patients with ulcerative colitis and Crohn's disease require special colorectal cancer screening programs.

Other people at higher than average risk for developing colorectal cancer are those born with a genetic propensity to develop multiple polyps, a condition called familial polyposis coli. At ages as young as 9 or 10 years old, hundreds to thousands of adenomatous (premalignant) polyps are found throughout the colon. While the polyps may be benign, they are precursors of cancer. This condition also requires special surveillance and treatment.

When colorectal cancer develops in a patient at an unusually young age (under 40) whose family has a history of other cancers such as endometrial, ovarian, breast, or prostate, it is called the cancer family syndrome. Formerly referred to as Lynch II families after the geneticist Dr. Henry Lynch, who identified this syndrome, these families require close surveillance once identified.

Hereditary non-polyposis colon cancer is another condition that may account for a significant portion of cancers in patients with a family history of the disease. Although few polyps may be found, multiple cancers can develop in younger people and in the children of affected parents.

A family or personal history of polyps may also increase your risk for developing polyps or colorectal cancer. It is important to know specifically what type of polyp a family member had and what type you had. The type of polyp dictates the follow-up.

Colon cancer is a fairly common cancer, so even if you do not have a genetic condition, colon cancer can run in families.Those with first degree relatives-parents, siblings or children-with colorectal cancer are at increased risk for the disease and require more intense surveillance. Knowing your family history is of paramount importance. It helps your physician target medical screening and surveillance to those areas that require closer scrutiny.

In recent years, other factors such as personal habits have been shown to increase the risk of colorectal cancer. Low fiber/ high fat diets, sedentary lifestyle with little regular exercise and obesity have been associated with a higher incidence of colorectal cancer.