What is Cancer
Cancer is a group of more than 100 diseases caused by the uncontrolled growth and spread of abnormal cells. Tumors, or abnormal growth of tissue, may be benign or malignant. Benign tumors are usually slow-growing and not life-threatening, whereas malignant tumors (or cancers) are made up of cells with abnormal genetic material (or DNA) and grow more rapidly. Malignant tumors have a tendency to invade neighboring tissues or organs and to travel and grow in other areas of the body; i.e. to metastasize. If the spread of the cancer is not stopped, cancer cells invade vital organs, which can result in death. Cancer cells may remain at their original site (local stage), spread to an adjacent area of the body (regional stage), or spread throughout the body (distant stage). Cancers at the local, regional or distant stage are considered invasive. A very early cancer found in only a few layers of cells, called in situ cancer, is considered non-invasive. (Please see the Glossary for definitions of many of these terms.)
What Causes Cancer
Cancers are caused by a variety of factors working alone or in combination. Some cancers are caused by external factors such as tobacco, diet, certain chemicals, radiation, and viruses and some by personal factors such as hormones, immune conditions, and inherited genetic mutations. Usually ten or more years pass between exposure to an external factor that causes cancer and the detectable disease.
Cancer Incidence and Mortality in the U.S.
Cancer is the second leading cause of death in the U.S. with about 1,221,100 new cases and 552,200 deaths estimated for 2000. Over the past 50 years, the overall death rate from cancer has increased due partially to a large rise in lung cancer death rates resulting from smoking. During the past few years, cancer rates have begun to decrease, possibly as a result of healthier lifestyles, particularly decreases in smoking. Cancer occurs in people of all ages, but its occurrence increases steadily in people over 45 years of age. However, in the U.S. cancer is also the leading cause of non-injury death among children under 15. In this country, men have about a 1 in 2 lifetime risk of developing cancer and women have about a 1 in 3 lifetime risk. These proportions do not include the majority of skin cancers that are not reportable to most cancer registries. In the U.S., men have higher cancer mortality rates than women, and blacks have the highest cancer mortality rate of any major racial group. A much higher percentage of people diagnosed with cancer are now surviving compared with people diagnosed in earlier years. More than six of every ten people diagnosed with cancer in recent years will survive for at least five years from the time of diagnosis.
Incidence in the U.S.
Colorectal cancer is the third most common type of cancer among men and women in the U.S., accounting for about 11 percent of all newly diagnosed cancer cases. It is estimated that over 130,200 new cases of colorectal cancer will be diagnosed in 2000 in the U.S. The overall age-adjusted incidence rate of colorectal cancer in the U.S. increased steadily between 1973 and 1985, after which overall colorectal cancer incidence declined. Regardless of race, colorectal cancer incidence rates are significantly higher in men than in women. Many researchers believe that the decrease in colorectal cancer incidence rates are due to changes in diet, such as the lower consumption of fat, red meat, and alcohol, and increased physical activity. Also, the use of non-steroidal anti-inflammatory drugs, including aspirin, may have contributed to the decline.7 Increased screening for colorectal cancer, may have contributed to the decreased incidence rates through early removal of non-malignant polyps that may later become cancerous.
Mortality in the U.S.
Colorectal cancer is the second most common cause of cancer death among men and the third among women, making it the second leading cause of cancer death in the U.S. with 56,300 deaths estimated for 2000. Since 1973 colorectal cancer mortality rates have steadily declined in the overall population.
Risk Factors for Colorectal Cancer
Other potential risk factors still under investigation include tobacco use, socio-economic status, age at first pregnancy, post-menopausal hormone replacement therapy, environmental exposures, and genetic factors. In actuality, it is a combination of many factors that determines an individual's risk for developing colorectal cancer.
All adults over the age of 50 should undergo regular colorectal cancer screening. Any person exhibiting one or more of the definitive risk factors (e.g. personal or family history) should begin regular screening earlier. There are several methods currently used to screen for early stages of colorectal cancer and pre-malignant conditions such as polyps. These methods have varying degrees of success in detecting colorectal cancer in different parts of the colon and rectum. (Note: see Figure 8 for a diagram of the colon and rectum.) A yearly fecal occult blood test (FOBT) detects small amounts of blood in the stool from any gastrointestinal source. As a result, the FOBT is not specific to colorectal cancer, but can be used to determine if a more specific test is necessary. A flexible sigmoidoscopy (Flex Sig) or sigmoidoscopy, provides a direct view of the distal colon, but does not detect polyps in the proximal colon. A Flex Sig is recommended every 5 years.
A colonoscopy provides a direct view of the entire colon and thus is the most comprehensive of all screening methods. The colonoscopy should be performed every 10 years and is performed under sedation. Finally, a double contrast barium enema (DCBA), with a recommended frequency of every 5 to 10 years, provides an x-ray image of the colon. In addition, virtual colonoscopies are currently being studied as less invasive and perhaps more accurate methods for detecting adenomatous polyps. Virtual colonoscopies include 2-dimensional and 3-dimensional computed tomographic colonography (CTC) and magnetic resonance colonography (MRC). The CTC is less promising because, under repeated screenings, it may expose the patient to elevated levels of radiation. Preliminary studies have shown the MRC and the conventional colonoscopy to have similar accuracy in polyp detection. Due to the high cost of the MRC, however, it would be most useful in screening of high-risk patients. A positive MRC would require that the patient undergo a conventional colonoscopy.9
Regular screening to detect and remove potentially cancerous polyps, combined with a healthy, low-fat diet is recommended to prevent colorectal cancer. Recent studies have had inconsistent results regarding the value of a diet high in fruits and vegetables for prevention of colorectal cancer. However, the value of these foods for preventing other diseases and maintaining overall health is indisputable. Physical activity is also important in maintaining overall health and may help to prevent colorectal cancer.
For additional free information on colorectal and other cancers these organizations may be contacted:
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