Colon & Rectal Cancer
From Diagnosis to Treatment
By Paul Ruggieri, Addison R. Tolentino, Jack Kusler
Addicus Books, Inc. Copyright © 2012 Paul Ruggieri, M.D., and Addison R. Tolentino, M.D.
All rights reserved.
Colorectal Cancer: An Overview
It seems nothing can prepare us for a diagnosis of cancer. Being told you have cancer can bring on a flood of emotions — shock, fear, and confusion. At first, it may be difficult to comprehend the fact that you have cancer. And, in addition to coming to grips with the diagnosis, you're faced with undergoing medical tests and a series of treatments, all of which you probably know little about. It can be a stressful time for you, your family, and friends.
The term "colorectal cancer" actually refers to two diseases. Colon cancer is cancer found in the tissues of the colon, and rectal cancer forms in the tissues of the rectum. Both cancers have the same characteristics and the same risk factors. In some cases, they are treated the same way, while at other times the treatments are different.
Colorectal Cancer Statistics
Not counting skin cancer, colon cancer is the third most commonly diagnosed cancer in the United States. It affects approximately 102,000 Americans each year, according to the American Cancer Society. Rectal cancer is less common than colon cancer, affecting nearly 40,000 people annually. Both cancers are curable if detected early. And, thanks to improved treatments and greater public awareness about preventive screening, death rates from colorectal cancer have been dropping over the last twenty years.
Anatomy and Function of the Colon and Rectum
Before discussing colorectal cancer and how it develops, let's first take a brief look at the anatomy of the colon and rectum. The colon and rectum are important parts of your gastrointestinal (GI) tract. This tract includes your mouth, esophagus, stomach, duodenum (first part of your small intestine), small intestine, colon (large intestine), rectum, and anus. This system takes in food, digests it, absorbs nutrients, and excretes waste.
The primary job of the colon is to manage and remove solid waste. When you eat, food spends several hours in the stomach being digested. Once the nutrients are absorbed in the small intestine, any remaining liquid enters the colon, which is also called the large bowel.
By the time the liquid enters the first part of the colon, it contains no nutrients and is pure waste product. This waste liquid is slowly propelled toward the rectum. Over a four- to six-hour period, the cells in the colon absorb remaining water from the waste material. The colon can absorb nearly two gallons of water a day. The end product is the solid waste, or feces.
The rectum's primary function is to store processed fecal material before it is excreted from the body. Once there is enough fecal material in the rectum, sensory nerves tell the brain it is time to have a bowel movement.
The colon is a hollow, tubelike organ that is five to six feet long and up to five inches in diameter. It sits in the abdominal cavity and is divided into segments. The first segment is the cecum, which is a pouch that receives waste material from the small intestine. The next segment is the right (ascending) colon, located on the right side of the abdomen. The transverse colon crosses over the midsection of the abdomen. The left (descending) colon is on the left side of the abdominal cavity. The left colon leads into the sigmoid colon, an S-shaped section that connects to the rectum. The rectum is a muscular tube, the last six to ten inches of the colon, and it exits into the anus.
The colon itself has four layers of tissue. The innermost layer, the mucosa, is in direct contact with fecal material moving through the colon and is responsible for much of the colon's function. The thin mucosa is composed of specialized cells that are in a constant state of flux, continually dying, sloughing off, and being replaced with new cells. The layer under the mucosa is the submucosa. It's a specialized layer of cells that helps support the mucosa.
The next layer of tissue is the muscularis propria. The muscle cells in this layer give strength to the colon wall and cause the contractions that push fecal material along the colon. The outermost layer of tissue is the serosa. The serosal cells add more support to the colon wall and act as a barrier, protecting the colon from any outside invading disease.
The rectum, the last six to ten inches of the colon, connects the colon to the anus. Unlike the rest of the colon, the walls of the rectum are primarily composed of muscle cells that propel the fecal material out of the body.
The last part of the digestive system is the anus. It is a canal, about two inches long, that contains sphincter muscles; it's the job of these muscles to hold in waste material until you're ready to have a bowel movement.
How Colorectal Cancer Develops
Colorectal cancer usually develops from polyps, which are small, abnormal growths that can occur anywhere along the gastrointestinal tract. Polyps are common in the colon and rectum; in fact, as many as 50 percent of the U.S. population has polyps in the colon and/or rectum. Polyps occur more frequently in people over age fifty; they are caused by genetic changes in the cells lining the inside of the colon and grow slowly over a period of ten to fifteen years. Cancer is an overgrowth of these abnormal cells and, sometimes, polyps start growing uncontrollably. Most people have no idea a tumor is growing inside their colon or rectum unless they go for routine tests or start to experience symptoms such as pain or bleeding.
Types of Polyps
Colorectal polyps may be benign or malignant (cancerous). Fortunately, most polyps are benign. Only about 1 percent of polyps that are removed prove to be cancerous. Still, it's important to know that benign polyps can turn into cancer if not removed.
Polyps referred to as benign are noncancerous. Several types of benign polyps may occur in the colon. The polyps are defined by their size and the appearance of their cells under the microscope.
Hyperplastic. About 90 percent of all polyps are hyperplastic polyps. They are small, about the size of a pea, and consist of a dense cluster of normal cells with no microscopic abnormalities. They are totally benign, with no potential to become cancerous.
Inflammatory. This type of benign polyp, also small, is made up of inflamed cells commonly associated with inflammatory diseases of the colon, including ulcerative colitis and Crohn's disease.
Hamartoma. This type of small, benign polyp is found in patients with genetically inherited polyp syndromes. (See discussion of these syndromes later in this chapter.) These polyps are frequently numerous and scattered throughout the colon.
A polyp can also be labeled precancerous. This means the growth contains suspicious-looking cells when viewed under the microscope, but these cells do not yet meet the criteria to be called malignant. If precancerous cells are not removed or treated, they can develop into cancer that can spread. These polyps are divided into three categories.
Tubular. This type of polyp may be found anywhere in the colon. Most are about one-fourth inch in diameter but may grow to three-fourths inch. They are made up of cells that are tubular in shape. Tubular polyps are generally considered premalignant with a 5 percent chance of becoming cancerous if not removed.
Tubulovillous. This type of polyp typically grows to about one-half inch in diameter and has a cluster of finger-like projections. These polyps have a higher potential — 20 percent — to turn into cancer.
Villous. These premalignant polyps are often found in the rectal area; they can grow to one to two inches in diameter. Villous polyps have the greatest potential — up to a 40 percent chance — to become malignant.
When a polyp is found to be cancerous, the cancer may be classified as carcinoma in situ or as adenocarcinoma.
Carcinoma in situ. These polyps contain cancer cells that are at the beginning of their life cycle. The malignant cells are contained within the polyp and do not spread to other organs.
Adenocarcinoma. These cancerous polyps have the potential to spread outside the polyp to other organs. This type of cancer is the most common form of colorectal cancer, making up nearly 96 percent of all cases.
Characteristics of Cancerous Polyps
Several factors influence whether a colorectal polyp is malignant. These factors include the size of the polyp, its shape, location, in the colon, and the presence or absence of microscopic changes to the DNA, the cell's blueprint for growth.
The larger the polyp, the greater the chance of it being cancerous. For instance, a polyp less than one-half inch in diameter has a less than 10 percent chance of being cancerous. However, polyps more than one inch in diameter can have a 20 to 30 percent chance of being cancerous. It is important to remove polyps early so they cannot grow to sizes that increase the potential for cancer.
The general shape of a colorectal polyp also influences the potential of it being cancerous. Polyps that are located on a "stalk," with the stalk attached to the inner lining of the colon wall, are easily removed and less likely to be cancerous. However, polyps that are very broad based are more difficult to remove and more likely to be cancerous. Broad-based polyps are called sessile polyps.
The location of a polyp is also important. Cancerous polyps are more commonly found in the sigmoid colon and rectum than in other parts of the colon. It has been estimated that more than 50 percent of cancerous polyps are located in the sigmoid colon and rectum; the sigmoid is the part of the large intestine that is closest to the rectum and anus.
Dysplasia is the medical term used to describe the genetic mutations (abnormalities) observed in the DNA of polyp cells. When cells are dysplastic their centers (nuclei) are misshapen. The more dysplastic changes, the greater the chance of finding cancer cells. Dysplastic changes can lead to cancerous tumors.
Symptoms of Colorectal Cancer
Early on, the symptoms of colorectal cancer often go unnoticed. You may feel fine, with no indication of any problem. Fortunately, routine screening often leads to the detection of colorectal cancer even when you have no symptoms.
By the time symptoms are obvious, colorectal cancer has often progressed. Unfortunately, many people ignore the signs and do not report them to their doctor. Some people do not realize that a change in bowel habits or blood in the stool may be a sign of cancer. Other people are embarrassed to talk about such symptoms. However, ignoring such symptoms may delay the early diagnosis of a potentially curable cancer.
Fatigue has many causes and is not always a symptom of colorectal cancer. However, when fatigue is caused by iron deficiency anemia, it may be a symptom of colorectal cancer. This anemia is caused by the body's not receiving enough iron to produce healthy red blood cells, which carry oxygen to the body's other cells. Such anemia could be the result of the slow, progressive loss of blood caused by a tumor. You may not notice the anemia right away, but it can lead to noticeable symptoms such as fatigue, pale appearance, dizziness, or shortness of breath during physical activity.
Change in Bowel Habits
A common early-warning symptom of colorectal cancer is a subtle change in your bowel habits. Changes in your bowel pattern may include:
Persistent loose stools.
Vague discomfort with bowel movements.
Changes in the shape of stools, such as pencil-thin stools.
A painful urge to have a bowel movement when it's not needed. This urge or feeling of incomplete evacuation of the bowels is known as tenesmus. It may be caused by a tumor growing inside the rectum that takes up space and creates pressure.
Passing bright red or dark blood is another warning symptom of colorectal cancer. The bleeding may be coming from a polyp or a cancer. You may notice blood on toilet paper or blood mixed in with a bowel movement; if the blood is mixed with stool, it may be dark, almost black, in color.
Passing blood may occur without pain. You may not even notice it if the blood loss is subtle and occurs slowly. It is possible that rectal bleeding could be caused by a hemorrhoid; however, it's important to report any rectal bleeding to your physician.
Abdominal Pain or Bloating
Abdominal pain is not a common warning symptom for colorectal cancer during its early stages. However, if the disease has spread beyond the colon or rectal wall into other organs, abdominal cramping and pain may occur. Individuals with this type of abdominal pain usually describe it as a dull, nagging, intermittent pain that does not go away with the use of over-the-counter antacids. Unfortunately, many people ignore such pain until it starts to impact their everyday activities. If you have recurrent pain, do not attribute it to an upset stomach, stress, or food choices. If the cancer should cause a perforation in the colon, the pain will likely worsen and may require a visit to an emergency room.
Other times, people may not feel pain, but will report feeling full after eating very little. If cancer has spread to the inner lining of the abdominal cavity, an accumulation of fluid may result. This may cause bloating or rapid distension of the belly. Sometimes, people say they can feel a mass in their abdomen that was never there before.
If you experience any of these symptoms, see your doctor.
Decreased Appetite, or Unintended Weight Loss
Some people with colorectal cancer complain of not having an appetite or of losing weight despite eating. It's possible that appetite could be affected by a tumor or fluid in the abdomen, causing you to feel full after eating very little. The reason that having cancer may cause weight loss is complex and not totally understood. It is believed that when you have cancer, the body releases destructive proteins, which leads to an increased metabolic rate, that is too high for sustaining body weight. Your body may not be absorbing all the fat, protein, and carbohydrates from the food you eat. Or your body may be burning calories faster than normal. The result is weight loss.
Sometimes, colorectal cancer will cause an abscess in the abdomen. Bacteria that reside in the colon can escape through the abscess and into the bloodstream. Having an infection in the bloodstream is a serious, life-threatening condition. It is referred to as bacteremia, or sepsis. Symptoms include chills, fever, drop in blood pressure, rapid heart rate, hyperventilation, light-headedness, and confusion. This condition requires emergency medical care.
Symptoms similar to those of a stroke are rarely the first symptoms of colorectal cancer. However, it is possible that some colorectal cancers may go undetected until the cancer has spread to parts of the brain. Symptoms would include stroke-like symptoms, such as weakness or numbness in the face, arm, or leg. Other possible symptoms are blurred vision, slurred speech, and seizures.
Risk Factors for Colorectal Cancer
What are the risks for developing colorectal cancer? No one knows exactly what causes colorectal cancer. However, doctors think genetic changes, coupled with dietary and environmental factors, play a role in normal cells changing into cancerous cells.
The following risk factors increase the chances for developing colorectal cancer sometime in your life. Fortunately, some of the risks are related to lifestyle, and making changes in lifestyle can decrease your risk.
A family history of colorectal cancer is the most important risk factor. According to the National Cancer Institute, 25 percent of individuals diagnosed with colon cancer have a family history of the disease. Having someone in your family with colorectal cancer, particularly a parent or sibling, puts you at a much higher risk than someone without a family history of the disease. If a relative such as an aunt, uncle, or cousin has had colorectal cancer, the risk is lower, but still higher than for those with no family history of the disease. (Continues...)
Excerpted from Colon & Rectal Cancer by Paul Ruggieri, Addison R. Tolentino, Jack Kusler. Copyright © 2012 Paul Ruggieri, M.D., and Addison R. Tolentino, M.D.. Excerpted by permission of Addicus Books, Inc..
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