Incidence of Colorectal Cancer
Colorectal cancer affects about 5% of the population, with up to 150,000 new cases per year in the United States alone. Cancer of the large intestine accounts for 21% of all cancers in the US, ranking second only to lung cancer in mortality in both males and females. It is, however, one of the most potentially curable of gastrointestinal cancers. Colorectal cancer is detected through screening procedures or when the patient presents with symptoms. Screening is vital to prevention and should be a part of routine care for adults over the age of 50 who are at average risk. High-risk individuals (those with previous colon cancer, family history of colon cancer, inflammatory bowel disease, or history of colorectal polyps) require careful follow-up.
There is great variability in the worldwide incidence and mortality rates. Industrialized nations appear to have the greatest risk while most developing nations have lower rates. Unfortunately, this incidence is on the increase. North America, Western Europe, Australia and New Zealand have high rates for colorectal neoplasms (Figure 1).
|Figure 1. Geographic distribution of sporadic colorectal cancer.|
Typical Causes of Colorectal Cancer
The development of cancer of the colon and rectum is thought to be influenced by diet, genetic, and environmental factors. The incidence of colorectal cancer increases with age beginning at 40 but remains relatively low until the age of 50 and then rapidly accelerates. This prevalence appears to double with each successive decade until about age 80. Those with a personal history of adenomas or colorectal cancer are at increased risk. Individuals with a family history of colorectal cancer or adenomas, various genetic polyposis and nonpolyposis syndromes, other cancers, and inflammatory bowel disease are also at higher risk of developing colorectal cancer. It is important to note, however, that most patients have no identifiable genetic risk factors (Figure 2).
|Figure 2. Incidence of types of colorectal cancer in the United States. |
Where in the colon does colorectal cancer occur?
Colorectal adenomas have a potential to progress to malignancy. Malignancy may spread by direct extension into other organs in the abdominal cavity. Invasion of the lymph vessels leads to lymph node metastases and invasion through the blood stream (hematogenous) can result in metastasis to distant sites such as the liver. Figure 3 illustrates the distribution of colorectal tumors.
|Figure 3. Frequency and location of colon and rectal cancers. |